Impact the slice() builtin can elide side effects when the output length is 0, and the source bytestring is a builtin (msg.data or <address>.code). the reason is that for these source locations, the check that length >= 1 is skipped: https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L315-L319

the result is that a 0-length bytestring constructed with slice can be passed to makebytearraycopier, which elides evaluation of its source argument when the max length is 0: https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/codegen/core.py#L189-L191

the impact is that side effects in the start argument may be elided when the length argument is 0, e.g. slice(msg.data, self.dosideeffect(), 0).

the following example illustrates how the issue would look in user code vyper counter: public(uint256)

@external def test() -> Bytes[10]: b: Bytes[10] = slice(msg.data, self.sideeffect(), 0) return b

def sideeffect() -> uint256: self.counter += 1 return 0

the severity assigned is low, since this is not a very useful pattern and unlikely to be found in user code.

Patches

the fix is tracked in https://github.com/vyperlang/vyper/pull/4645, which disallows any invocation of slice() with length 0, including for the ad hoc locations discussed in this advisory.

Workarounds Is there a way for users to fix or remediate the vulnerability without upgrading?

References Are there any links users can visit to find out more?

Impact concat() may skip evaluation of side effects when the length of an argument is zero. this is due to a fastpath in the implementation which skips evaluation of argument expressions when their length is zero: https://github.com/vyperlang/vyper/blob/68b68c4b30c5ef2f312b4674676170b8a6eaa316/vyper/builtins/functions.py#L560-L562

in practice, it would be very unusual in user code to construct zero-length bytestrings using an expression with side-effects, since zero-length bytestrings are typically constructed with the empty literal b""; the only way to construct an empty bytestring which has side effects would be with the ternary operator introduced in v0.3.8, e.g. b"" if self.dosomesideeffect() else b"".

the following example demonstrates how the issue would look in user code vyper counter: public(uint256)

@external def test() -> Bytes[256]: a: Bytes[256] = concat(b"" if self.sideeffect() else b"", b"aaaa") return a

def sideeffect() -> bool: self.counter += 1 return True

the severity assigned is low, since, as mentioned, this would be a very unusual pattern in user-code.

Patches

fix is tracked in https://github.com/vyperlang/vyper/pull/4644

Workarounds don't have side effects in expressions which construct zero-length bytestrings.

References Are there any links users can visit to find out more?

Summary

When the Vyper Compiler uses the precompiles EcRecover (0x1) and Identity (0x4), the success flag of the call is not checked. As a consequence an attacker can provide a specific amount of gas to make these calls fail but let the overall execution continue. Then the execution result can be incorrect.

Based on EVM's rules, after the failed precompile the remaining code has only 1/64 of the pre-call-gas left (as 63/64 were forwarded and spent). Hence, only fairly simple executions can follow the failed precompile calls. Therefore, we found no significantly impacted real-world contracts.

The fix is tracked in https://github.com/vyperlang/vyper/pull/4451.

Details

The relevant precompiles

EcRecover

EcRecover is used in vyper's ecrecover built-in. As the precompile consumes 3000 gas, any execution after an out-of-gas EcRecover call has at most 47 gas left.

Identity

- The Identity precompile is used in vyper to perform memory copy operations. As its cost is variable, a variable amount of gas might be left after a failed call. The bigger the copy operation, the more gas can be left. Hence, a failed call to Identity could theoretically be followed by successful storage changes or emitted events. - Identity is no longer used when evm-version cancun is used (because MCOPY is used instead). In 0.4.0 cancun is default, in 0.3.10 cancun is an option, otherwise cancun is not available. As only pre-cancun versions are relevant, we don't have to consider transient storage operations succeeding a failed call to Identity.

The other precompiles

- Calls to Sha2, ecAdd, and ecMul have success checks and have had them for a long time. - The precompiles modexp, ripe, blake, ecPairing, and Point Evaluation have no builtins in vyper.

PoC

In the following we provide concrete examples of incorrectly generated bytecode. These examples are not optimized, but rather Proof-of-Concepts. The list is also not exhaustive.

ecrecover use

- Affected versions: 0.2.0 - 0.4.0 - For older compiler versions (<=0.3.9) it behaves similarly to this older advisory. As no data is returned, the previous value of the memory word is returned to the user. Hence, any dirty bytes might be returned. Contracts with older compiler versions and ecrecover were checked. - For new vyper versions, the output buffer is zeroed, so when the call fails zero is returned. This is an incorrect result, but developers should anyway check for 0 as a failure case. Hence, this is unlikely to result in issues. However, we did search for such cases. - As mentioned above at most 47 gas is left after the failed call, hence a return is the most realistic scenario to be attacked.

Vulnerable Code: py @external @view def foo(hash: bytes32, v: uint256, r:uint256, s:uint256) -> address: return ecrecover(hash, v, r, s)

Problematic Call: py print( c.foo( binascii.unhexlify( "6c9c5e133b8aafb2ea74f524a5263495e7ae5701c7248805f7b511d973dc7055" ), 28, 78616903610408968922803823221221116251138855211764625814919875002740131251724, 37668412420813231458864536126575229553064045345107737433087067088194345044408, ) ) # Returns 0x9eE53ad38Bb67d745223a4257D7d48cE973FeB7A

print( c.foo( binascii.unhexlify( "6c9c5e133b8aafb2ea74f524a5263495e7ae5701c7248805f7b511d973dc7055" ), 28, 78616903610408968922803823221221116251138855211764625814919875002740131251724, 37668412420813231458864536126575229553064045345107737433087067088194345044408, gas=3000, ) ) # Returns 0x0000000000000000000000000000000000000000

Identity to copy Dynamic Arrays

- Affected versions: 0.3.2 - 0.3.9 - Dynamic Arrays might be copied on different occasions - That copy operation can fail leading to incorrect accesses afterwards

Vulnerable Code: py

@external def foo() -> uint256: a: DynArray[uint256, 4000] = [2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] b: DynArray[uint256, 4000] = a return b[0]

Problematic Call: py print(c.foo()) # Prints 2 print(c.foo(gas=170000)) # Prints 0

Identity in ABI Encoding of Returndata

- Affected versions: 0.3.2 - 0.4.0 - Complex types such as Dynamic array with Strings inside need to be abi encoded before being returned - In that return there is a memory copy which can fail

Vulnerable Code: py @external @view def foo(x: String[1000000], y: String[1000000]) -> DynArray[String[1000000], 2]: z: DynArray[String[1000000], 2] = [x, y] # Some code return z

Problematic Call: py calldata0 = "a"10 calldata1 = "b"1000000 c.foo(calldata0, calldata1) # Returns correct data c.foo(calldata0, calldata1, gas=48400000) # Returns incorrect data (only first part)

Assertion based on data copied through Identity

- Affected versions: 0.2.0 - 0.4.0 - An incomplete copy operation might falsify the result of a subsequent assert

Vulnerable Code: py @internal def bar() -> uint256[3000]: a: uint256[3000] = [2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 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0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] return a

@external def foo(): s: uint256[3000] = self.bar() assert(s[0] == 0)

Problematic Call: py try: c.foo() # Correctly reverts except Exception as e: print("Correctly reverted") try: c.foo(gas=210000) # Incorrectly succeeds print("Incorrectly succeeded") except Exception: pass

Identity used in rawrevert

- Affected versions: 0.3.8 - 0.4.0 - A copy operation might appear as part of rawrevert - As a result the revert reason might be incorrect

Vulnerable Code: py @external def foo(data: Bytes[10000]): b: Bytes[10000] = data rawrevert(b)

Problematic Call: py calldata = binascii.unhexlify("bb" 10000) c.foo(calldata) # Has correct revert reason c.foo(calldata, gas=4800) # Has empty revert reason, but not out-of-gas

Identity to copy static arrays

- Affected versions: 0.2.0 - 0.4.0 - Vyper might perform a memory copy for static arrays, e.g. when moving them in and out of internal functions - As this access is especially cheap (due to the static checks) it can also happen for smaller sizes

Vulnerable Code: py @external def foo(x: uint256[2500]) -> uint256: s: uint256[2500] = x t: uint256[2500] = s return t[0]

Problematic Call: py calldata = [2] + [0] 2499 print(c.foo(calldata)) # Prints 2 print(c.foo(calldata, gas=74500)) # Prints 0

Identity to copy and return String or Bytes

- Affected versions: 0.20 - 0.4.0 - Multiple situations in vyper might trigger a memory copy operation, e.g. moving data in and out of internal functions - If the target buffer is later returned, incorrect data might be returned

Vulnerable Code: py @external @view def foo(x: String[1000000]) -> String[1000000]: return x

Problematic Call: py calldata = "a"1000000 x = c.foo(calldata) # Returns calldata y = c.foo(calldata, gas=8000000) # Returns empty data

Identity and accessing the length of the target data

- Affected versions: 0.3.10 - 0.4.0 - Accessing the data is fairly cheap, making it possible for smaller data copies

Vulnerable Code: py @external @view def foo(x: String[1000000]) -> uint256: y: String[1000000] = x return len(y)

Problematic Call: py calldata = "a"1000000 x = c.foo(calldata) # Returns correct length y = c.foo(calldata, gas=7929200) # Returns incorrect length

Identity to copy and return String or Bytes

- Affected versions: 0.3.10 - 0.4.0 - Multiple situations in vyper might trigger a memory copy operation, e.g. moving data in and out of internal functions - If the target buffer is later returned, incorrect data might be returned

Vulnerable Code: py @external @view def foo(x: String[1000000]) -> String[1000000]: return x

Problematic Call: py calldata = "a"1000000 x = c.foo(calldata) # Returns calldata y = c.foo(calldata, gas=8000000) # Returns empty data

Impact

A contract search was conducted and yielded no significant results.

The advisory was rated a medium because the likelihood is low, but difficult to detect by source code analysis alone, and could yield unexpected results if a contract is affected by the bug.

Summary Using the sqrt builtin can result in multiple eval evaluation of side effects when the argument has side-effects. The bug is more difficult (but not impossible!) to trigger as of 0.3.4, when the unique symbol fence was introduced (https://github.com/vyperlang/vyper/pull/2914).

A contract search was performed and no vulnerable contracts were found in production.

Details It can be seen that the buildIR function of the sqrt builtin doesn't cache the argument to the stack: https://github.com/vyperlang/vyper/blob/4595938734d9988f8e46e8df38049ae0559abedb/vyper/builtins/functions.py#L2151

As such, it can be evaluated multiple times (instead of retrieving the value from the stack).

PoC With at least Vyper version 0.2.15+commit.6e7dba7 the following contract: vyper c: uint256

@internal def somedecimal() -> decimal: self.c += 1 return 1.0

@external def foo() -> uint256: k: decimal = sqrt(self.somedecimal()) return self.c passes the following test: solidity // SPDX-License-Identifier: MIT pragma solidity >=0.8.13;

import "../../lib/ds-test/test.sol"; import "../../lib/utils/Console.sol"; import "../../lib/utils/VyperDeployer.sol";

import "../ITest.sol";

contract ConTest is DSTest { VyperDeployer vyperDeployer = new VyperDeployer();

ITest t;

function setUp() public { t = ITest(vyperDeployer.deployContract("Test")); }

function testFoo() public { uint256 val = t.foo(); console.log(val); assert (val == 4); } } Patches Patched in https://github.com/vyperlang/vyper/pull/3976.

Impact No vulnerable production contracts were found.

Summary Prior to v0.3.0, default() functions did not respect the @nonreentrancy decorator and the lock was not emitted. This is a known bug and was already visible in the issue tracker (https://github.com/vyperlang/vyper/issues/2455), but it is being re-issued as an advisory so that tools relying on the advisory publication list can incorporate it into their searches.

A contract search was additionally performed and no vulnerable contracts were found in production.

PoC vyper @external @payable @nonreentrant("default") def default(): pass

after codegen: [seq, [if, [lt, calldatasize, 4], [goto, fallback]], [mstore, 28, [calldataload, 0]], [with, funcsig, [mload, 0], seq], [sequnchecked, [label, fallback], [seq, pass, # Line 5 pass, pass, # Line 4 stop]]],

Impact No vulnerable production contracts were found. Additionally, using a lock on a default function is a very sparsely used pattern. As such, the impact is low.

Summary Using the createfromblueprint builtin can result in a double eval vulnerability when rawargs=True and the args argument has side-effects.

A contract search was performed and no vulnerable contracts were found in production. In particular, the rawargs variant of createfromblueprint was not found to be used in production.

Details It can be seen that the buildcreateIR function of the createfromblueprint builtin doesn't cache the mentioned args argument to the stack: https://github.com/vyperlang/vyper/blob/cedf7087e68e67c7bfbd47ae95dcb16b81ad2e02/vyper/builtins/functions.py#L1847

As such, it can be evaluated multiple times (instead of retrieving the value from the stack).

PoC The vulnerability is demonstrated in the following boa test: vyper src1 = """ c: uint256 """ deployer = """ createdaddress: public(address) deployed: public(uint256)

@external def get() -> Bytes[32]: self.deployed += 1 return b''

@external def create(target: address): self.createdaddress = createfromblueprint(target, rawcall(self, methodid("get()"), maxoutsize=32), rawargs=True, codeoffset=3) """

Factory = b.loadspartial(src1) c = Factory.deployasblueprint()

c2 = b.loads(deployer, b'') c2.create(c) c2.deployed() The output of c2.deployed() is 2 although create was called only once and the value was initialized to 0.

Patches Patched in https://github.com/vyperlang/vyper/pull/3976.

Impact No vulnerable production contracts were found. Additionally, double evaluation of side-effects should be easily discoverable in client tests. As such, the impact is low.

Summary Using the slice builtin can result in a double eval vulnerability when the buffer argument is either msg.data, self.code or <address>.code and either the start or length arguments have side-effects.

A contract search was performed and no vulnerable contracts were found in production. Having side-effects in the start and length patterns is also an unusual pattern which is not that likely to show up in user code. It is also much harder (but not impossible!) to trigger the bug since 0.3.4 since the unique symbol fence was introduced (https://github.com/vyperlang/vyper/pull/2914).

Details It can be seen that the buildadhocslicenode function of the slice builtin doesn't cache the mentioned arguments to the stack: https://github.com/vyperlang/vyper/blob/4595938734d9988f8e46e8df38049ae0559abedb/vyper/builtins/functions.py#L244

As such, they can be evaluated multiple times (instead of retrieving the value from the stack).

PoC with Vyper version 0.3.3+commit.48e326f the call to foo passes the asserts: vyper l: DynArray[uint256, 10]

@external def foo(cs: String[64]) -> uint256: for i in range(10): self.l.append(1) assert len(self.l) == 10 s: Bytes[64] = b"" s = slice(msg.data, self.l.pop(), 3) assert len(self.l) == 10 - 2 return len(self.l)

Patches Patched in https://github.com/vyperlang/vyper/pull/3976.

Impact No vulnerable production contracts were found.

Summary Incorrect values can be logged when rawlog builtin is called with memory or storage arguments to be used as topics.

A contract search was performed and no vulnerable contracts were found in production. In particular, no uses of rawlog() were found at all in production; it is apparently not a well-known function.

Details The buildIR function of the RawLog class fails to properly unwrap the variables provided as topics. Consequently, incorrect values are logged as topics.

PoC vyper x: bytes32

@external def f(): self.x = 0x1234567890123456789012345678901234567890123456789012345678901234 rawlog([self.x], b"") # LOG1(offset:0x60, size:0x00, topic1:0x00)

y: bytes32 = 0x1234567890123456789012345678901234567890123456789012345678901234 rawlog([y], b"") # LOG1(offset:0x80, size:0x00, topic1:0x40) Patches Fixed in https://github.com/vyperlang/vyper/pull/3977.

Impact Incorrect values can be logged which may result in unexpected behavior in client-side applications relying on these logs.

Summary

When looping over a range of the form range(start, start + N), if start is negative, the execution will always revert. Details

This issue is caused by an incorrect assertion inserted by the code generation of the range (stmt.parseForrange()):

https://github.com/vyperlang/vyper/blob/9136169468f317a53b4e7448389aa315f90b95ba/vyper/codegen/stmt.py#L286-L287

This assertion was introduced in https://github.com/vyperlang/vyper/commit/3de1415ee77a9244eb04bdb695e249d3ec9ed868 to fix https://github.com/advisories/GHSA-6r8q-pfpv-7cgj. The issue arises when start is signed, instead of using sle, le is used and start is interpreted as an unsigned integer for the comparison. If it is a negative number, its 255th bit is set to 1 and is hence interpreted as a very large unsigned integer making the assertion always fail. PoC

Vyper @external def foo(): x:int256 = minvalue(int256) # revert when it should not since we have the following assertion that fails: # [assert, [le, minvalue(int256), maxvalue(int256) + 1 - 10]], for i in range(x, x + 10): pass

Patches

patched in v0.4.0, specifically, https://github.com/vyperlang/vyper/pull/3679 disallows this form of range().

Impact

Any contract having a range(start, start + N) where start is a signed integer with the possibility for start to be negative is affected. If a call goes through the loop while supplying a negative start the execution will revert.

Impact contracts containing large arrays might underallocate the number of slots they need. prior to v0.3.8, the calculation to determine how many slots a storage variable needed used math.ceil(type.sizeinbytes / 32):

https://github.com/vyperlang/vyper/blob/6020b8bbf66b062d299d87bc7e4eddc4c9d1c157/vyper/semantics/validation/datapositions.py#L197

the intermediate floating point step can produce a rounding error if there are enough bits set in the IEEE-754 mantissa. roughly speaking, if type.sizeinbytes is large (> 246), and slightly less than a power of 2, the calculation can overestimate how many slots are needed. if type.sizeinbytes is slightly more than a power of 2, the calculation can underestimate how many slots are needed.

the following two example contracts can result in overwriting of the variable vulnerable: vyper largearray: address[264 + 1] # type.sizeinbytes == 32 (264 + 1); math.ceil(type.sizeinbytes / 32) < 264 + 1 vulnerable: uint256

writing to self.largearray[264] will overwrite self.vulnerable vyper largedynarray: DynArray[address, 264] # Dynarray has a length word in front, its size in bytes is 32 (264 + 1) vulnerable: uint256

writing to self.largedynarray[264 - 1] will overwrite self.vulnerable

note that in the latter case, the risk of vulnerable being overwritten is relatively small, since it would cost roughly $1.45 million trillion USD at today's gas prices (gas price 20gwei, ETH ~= $1800) in order to extend the DynArray to its full container size.

Patches patched by v0.3.8, specifically in commit https://github.com/vyperlang/vyper/commit/0bb7203b584e771b23536ba065a6efda457161bb.

Impact abidecode() does not validate input when it is nested in an expression. the following example gets correctly validated (bounds checked): vyper x: int128 = abidecode(slice(msg.data, 4, 32), int128)

however, the following example is not bounds checked vyper @external def abidecode(x: uint256) -> uint256: a: uint256 = convert(abidecode(slice(msg.data, 4, 32), (uint8)), uint256) + 1 return a # abidecode(256) returns: 257

the issue can be triggered by constructing an example where the output of abidecode is not internally passed to makesetter (an internal codegen routine) or other input validating routine.

Patches https://github.com/vyperlang/vyper/pull/3626

Workarounds Is there a way for users to fix or remediate the vulnerability without upgrading?

References Are there any links users can visit to find out more?

Impact In certain conditions, the memory used by the builtins rawcall, createfromblueprint and createcopyof can be corrupted.

- For rawcall, the argument buffer of the call can be corrupted, leading to incorrect calldata in the sub-context. - For createfromblueprint and createcopyof, the buffer for the to-be-deployed bytecode can be corrupted, leading to deploying incorrect bytecode.

Below are the conditions that must be fulfilled for the corruption to happen for each builtin:

rawcall - memory is not fully initialized, ex. all parameters to an external function live in calldata and - The data argument of the builtin is msg.data. and - The to, value or gas passed to the builtin is some complex expression that results in writing to uninitialized memory (e.g. calling an internal function)

createcopyof - memory is not fully initialized, ex. all parameters to an external function live in calldata and - The value or salt passed to the builtin is some complex expression that results in writing to uninitialized memory (e.g. calling an internal function)

createfromblueprint - memory is not fully initialized, ex. all parameters to an external function live in calldata and - Either no constructor parameters are passed to the builtin or rawargs is set to True. and - The value or salt passed to the builtin is some complex expression that results in writing to uninitialized memory (e.g. calling an internal function)

Note: When the builtin is being called from an internal function f from a function g, the issue is not present provided that g has written to memory before calling f. Examples

rawcall

In the following contract, calling bar(1,1) will return:

Python ae42e95100000000000000000000000000000000000000000000000000000000ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff00000001 instead of: Python ae42e95100000000000000000000000000000000000000000000000000000000000000010000000000000000000000000000000000000000000000000000000000000001

Python identity: constant(address) = 0x0000000000000000000000000000000000000004

@external def foo(): pass

@internal @view def getaddress()->address: a:uint256 = maxvalue(uint256) # 0xfff...fff return identity @external def bar(f:uint256, u:uint256) -> Bytes[100]: a: Bytes[100] = rawcall(self.getaddress(), msg.data, maxoutsize=100) return a

createcopyof In the following contract, after calling test(), the code deployed at self.createdaddress does not match the bytecode at target.

Vyper createdaddress: public(address)

@external def test(target: address) -> address: # The expression in salt= is complex and will require to store to memory self.createdaddress = createcopyof(target, salt = keccak256(abiencode(target))) return self.createdaddress

createfromblueprint In the following contract, after calling test(), the init bytecode used to create the contract deployed at the address self.createdaddress will not match the blueprint bytecode stored at target.

Vyper createdaddress: public(address)

salt: constant(bytes32) = keccak256("kebab")

@external @payable def test(target: address): # The expression in salt= is complex and will require to store to memory self.createdaddress = createfromblueprint(target, codeoffset=0, salt=keccak256(abiencode(target))) Patches issue tracking in https://github.com/vyperlang/vyper/issues/3609, patched in #3610

Workarounds

The complex expressions that are being passed as kwargs to the builtin should be cached in memory prior to the call to the builtin. For the last example above, it would be:

Vyper createdaddress: public(address)

salt: constant(bytes32) = keccak256("kebab")

@external @payable def test(target: address): salt: bytes32 = keccak256(abiencode(target)) self.createdaddress = createfromblueprint(target, codeoffset=0, salt=salt) References Are there any links users can visit to find out more?

Impact

Locks of the type @nonreentrant("") or @nonreentrant('') do not produce reentrancy checks at runtime.

Vyper @nonreentrant("") # unprotected @external def bar(): pass

@nonreentrant("lock") # protected @external def foo(): pass Patches

Patched in #3605

Workarounds

The lock name should be a non-empty string.

References Are there any links users can visit to find out more?

Impact The order of evaluation of the arguments of the builtin functions uint256addmod, uint256mulmod, ecadd and ecmul does not follow source order. • For uint256addmod(a,b,c) and uint256mulmod(a,b,c), the order is c,a,b. • For ecadd(a,b) and ecmul(a,b), the order is b,a.

Note that this behaviour is problematic when the evaluation of one of the arguments produces side effects that other arguments depend on.

Patches https://github.com/vyperlang/vyper/pull/3583

Workarounds When using builtins from the list above, make sure that the arguments of the expression do not produce side effects or, if one does, that no other argument is dependent on those side effects.

References Are there any links users can visit to find out more?

Impact

For the following (probably non-exhaustive) list of expressions, the compiler evaluates the arguments from right to left instead of left to right.

- unsafeadd - unsafesub - unsafemul - unsafediv - powmod256 - |, &, ^ (bitwise operators) - bitwiseor (deprecated) - bitwiseand (deprecated) - bitwisexor (deprecated) - rawcall - <, >, <=, >=, ==, != - in, not in (when lhs and rhs are enums)

This behaviour becomes a problem when the evaluation of one of the arguments produces side effects that other arguments depend on. The following expressions can produce side-effect:

- state modifying external call - state modifying internal call - rawcall - pop() when used on a Dynamic Array stored in the storage - createminimalproxyto - createcopyof - createfromblueprint

For example:

Vyper f:uint256

@internal def sideeffect() -> uint256: self.f = 12 return 1

@external def foo() -> uint256: return unsafeadd(self.f,self.sideeffect()) # returns 13 instead of 1

Vyper a:DynArray[uint256, 12] @external def bar() -> bool: self.a = [1,2,3] return len(self.a) == self.a.pop() # return false instead of true

Patches not yet patched, will address in a future release. tracking in https://github.com/vyperlang/vyper/issues/3604.

Workarounds

When using expressions from the list above, make sure that the arguments of the expression do not produce side effects or, if one does, that no other argument is dependent on those side effects.

References Are there any links users can visit to find out more?

Impact

In versions 0.2.15, 0.2.16 and 0.3.0, named re-entrancy locks are allocated incorrectly. Each function using a named re-entrancy lock gets a unique lock regardless of the key, allowing cross-function re-entrancy in contracts compiled with the susceptible versions. A specific set of conditions is required to result in misbehavior of affected contracts, specifically:

- A .vy contract compiled with either of the following vyper versions: 0.2.15, 0.2.16, 0.3.0 - A primary function that utilizes the @nonreentrant decorator with a specific key and does not strictly follow the check-effects-interaction pattern (i.e. contains an external call to an untrusted party before storage updates) - A secondary function that utilizes the same key and would be affected by the improper state caused by the primary function

Patches https://github.com/vyperlang/vyper/pull/2439, https://github.com/vyperlang/vyper/pull/2514

Workarounds Upgrade to 0.3.1 or higher

References Technical post-mortem report: https://hackmd.io/@vyperlang/HJUgNMhs2

Impact the ecrecover precompile does not fill the output buffer if the signature does not verify, see https://github.com/ethereum/go-ethereum/blob/b058cf454b3bdc7e770e2b3cec83a0bcb48f55ee/core/vm/contracts.go#L188. however, the ecrecover builtin will still return whatever is at memory location 0.

this means that the if the compiler has been convinced to write to the 0 memory location with specially crafted data (generally, this can happen with a hashmap access or immutable read) just before the ecrecover, a signature check might pass on an invalid signature.

A contract search was performed. Most uses of ecrecover are used for erc2612-style permit implementations, which typically look like:

vyper assert owner != empty(address) assert block.timestamp <= deadline nonce: uint256 = self.nonces[owner] digest: bytes32 = keccak256( concat( b"\x19\x01", self.DOMAINSEPARATOR, keccak256(abiencode(PERMITTYPEHASH, owner, spender, value, nonce, deadline)) ) ) assert ecrecover(digest, convert(v, uint256), convert(r, uint256), convert(s, uint256)) == owner

in this case, the immutable PERMITTYPEHASH is loaded into ecrecover's output buffer right before ecrecover(), and so the output of ecrecover() here when the signature is invalid will be the value of PERMITTYPEHASH. in this case, since PERMITTYPEHASH is not a valid address, it will never compare == to owner, and so the behaviour is exactly the same as if ecrecover() returned 0 in this case.

in general, a contract could have unexpected behavior (i.e. mistakenly pass this style of signature check) if an immutable representing a real address (ex. OWNER) was read right before the ecrecover operation.

Patches v0.3.10 (with 019a37ab98ff53f04fecfadf602b6cd5ac748f7f and #3586)

Workarounds Is there a way for users to fix or remediate the vulnerability without upgrading?

References Are there any links users can visit to find out more?

Impact in contracts with at least one regular nonpayable function, due to the callvalue check being inside of the selector section, it is possible to send funds to the default function by using less than 4 bytes of calldata, even if the default function is marked nonpayable. this applies to contracts compiled with vyper<=0.3.7. vyper @version 0.3.7

implicitly nonpayable @external def foo() -> uint256: return 1

implicitly nonpayable @external def default(): # could receive ether here pass

Patches this was fixed by the removal of the global calldatasize check in https://github.com/vyperlang/vyper/commit/02339dfda0f3caabad142060d511d10bfe93c520.

Workarounds don't use nonpayable default functions

Impact

Internal calls to internal functions with more than 1 default argument are compiled incorrectly. Depending on the number of arguments provided in the call, the defaults are added not right-to-left, but left-to-right. If the types are incompatible, typechecking is bypassed. In the bar() function in the following code, self.foo(13) is compiled to self.foo(13,12) instead of self.foo(13,1337).

vyper @internal def foo(a:uint256 = 12, b:uint256 = 1337): pass

@internal def bar(): self.foo(13)

note that at the time of publication, the ability to pass kwargs to internal functions is an undocumented feature that does not seem to be widely used.

Patches patched in c3e68c302aa6e1429946473769dd1232145822ac

Workarounds Is there a way for users to fix or remediate the vulnerability without upgrading?

References Are there any links users can visit to find out more?

Impact

Due to missing overflow check for loop variables, by assigning the iterator of a loop to a variable, it is possible to overflow the type of the latter.

In the following example, calling test returns 354, meaning that the variable a did store 354 a value out of bound for the type uint8.

Vyper @external def test() -> uint16: x:uint8 = 255 a:uint8 = 0 for i in range(x, x+100): a = i return convert(a,uint16)

The issue seems to happen only in loops of type for i in range(a, a + N) as in loops of type for i in range(start, stop) and for i in range(stop), the compiler is able to raise a TypeMismatch when trying to overflow the variable.

thanks to @trocher for reporting

Patches

patched in 3de1415ee77a9244eb04bdb695e249d3ec9ed868

Workarounds

Impact during codegen, the length word of a dynarray is written before the data, which can result in OOB array access in the case where the dynarray is on both the lhs and rhs of an assignment. here is a minimal example producing the issue: vyper a:DynArray[uint256,3] @external def test() -> DynArray[uint256,3]: self.a = [1,2,3] self.a = empty(DynArray[uint256,3]) self.a = [self.a[0],self.a[1],self.a[2]] return self.a # return [1,2,3]

and here is an example demonstrating the issue can cause data corruption across call frames:

vyper @external def test() -> DynArray[uint256,3]: self.a() return self.b() # return [1,2,3]

@internal def a(): a: uint256 = 0 b: uint256 = 1 c: uint256 = 2 d: uint256 = 3

@internal def b() -> DynArray[uint256,3]: a: DynArray[uint256,3] = empty(DynArray[uint256,3]) a = [a[0],a[1],a[2]] return a

examples involving append and pop: vyper @internal def foo(): c: DynArray[uint256, 1] = [] c.append(c[0])

vyper @internal def foo(): c: DynArray[uint256, 1] = [1] c[0] = c.pop()

the expected behavior in all of the above cases is to revert due to oob array access.

Patches patched in 4f8289a81206f767df1900ac48f485d90fc87edb

Workarounds Is there a way for users to fix or remediate the vulnerability without upgrading?

References Are there any links users can visit to find out more?

Impact The storage allocator does not guard against allocation overflows. This can result in vulnerabilities like the following: vyper owner: public(address) takeupsomespace: public(uint256[10]) buffer: public(uint256[maxvalue(uint256)])

@external def initialize(): self.owner = msg.sender

@external def foo(idx: uint256, data: uint256): self.buffer[idx] = data Per @toonvanhove, "An attacker can overwrite the owner variable by calling this contract with calldata: 0x04bc52f8 fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff5 ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff (spaces inserted for readability) 0x04bc52f8 is the selector for foo(uint256, uint256), and the last argument fff...fff is the new value for the owner variable."

Patches patched in 0bb7203b584e771b23536ba065a6efda457161bb

Workarounds Is there a way for users to fix or remediate the vulnerability without upgrading?

References Are there any links users can visit to find out more?

Background During the audit of Lido's Gate Seals code statemind team identified a weird behavior of the code that uses rawcall: https://github.com/lidofinance/gate-seals/blob/051593e74df01a4131c485b4fda52e691cd4b7d8/contracts/GateSeal.vy#L164 .

Construction like this: vyper success = rawcall( sealable, abiencode(SEALDURATIONSECONDS, methodid=methodid("pauseFor(uint256)")), revertonfailure=False ) was not fully documented: https://docs.vyperlang.org/en/v0.3.7/built-in-functions.html#rawcall .

The documentation says that: if maxoutsize=0 it should return nothing and then it says that if revertonfailure=False it should return a success flag in the tuple of response, but what if maxoutsize=0 and revertonfailure=False.

<img width="715" alt="image" src="https://user-images.githubusercontent.com/22330612/232125364-d2b3bbac-0b4f-40cb-80ff-f55d8eafef44.png">

So the team started researching what exactly happened in that case, after some research we found that the Vyper compiler generates the wrong bytecode in that case, it generates the sequence: CALL // call MLOAD // MLOAD is wrong since the CALL result is already stored in the stack

Impact Example of buggy code: vyper @external def returnSome(calling: address, a: uint256) -> bool: success: bool = false success = rawcall( calling, abiencode(a, methodid=methodid("a(uint256)")), revertonfailure=False )

any contract that uses the rawcall with revertonfailure=False and maxoutsize=0 receives the wrong response from rawcall. Depending on the memory garbage, the result can be either True or False.

Patches Fix by @charles-cooper https://github.com/vyperlang/vyper/commit/851f7a1b3aa2a36fd041e3d0ed38f9355a58c8ae

Workarounds The simple workaround is always to put maxoutsize>0. Workaround example https://github.com/lidofinance/gate-seals/pull/5/files

References Lido's fix: https://github.com/lidofinance/gate-seals/pull/5/files

Impact when a calling an external contract with no return value, the contract address could be evaluated twice. this is usually only an efficiency problem, but if evaluation of the contract address has side effects, it could result in double evaluation of the side effects.

in the following example, Foo(msg.sender).bar() is the contract address for the following call (to .foo()), and could get evaluated twice

vyper interface Foo: def foo(): nonpayable def bar() -> address: nonpayable

@external def dostuff(): Foo(Foo(msg.sender).bar()).foo()

Patches 6b4d8ff185de071252feaa1c319712b2d6577f8d

Workarounds assign contract addresses to variables. the above example would change to vyper @external def dostuff(): t: Foo = Foo(msg.sender).bar() t.foo()

References

For more information

Vyper is a pythonic Smart Contract Language for the ethereum virtual machine. In affected versions, the return of <iface>.returnsint128() is not validated to fall within the bounds of int128. This issue can result in a misinterpretation of the integer value and lead to incorrect behavior. As of v0.3.0, <iface>.returnsint128() is validated in simple expressions, but not complex expressions. Users are advised to upgrade. There is no known workaround for this issue.

Impact Importing a function from a JSON interface which returns bytes generates bytecode which does not clamp bytes length, potentially resulting in a buffer overrun.

Patches 0.3.2 (as of https://github.com/vyperlang/vyper/commit/049dbdc647b2ce838fae7c188e6bb09cf16e470b)

Workarounds Use .vy interfaces.

Vyper is a Pythonic Smart Contract Language for the Ethereum Virtual Machine. In version 0.3.1 and prior, bytestrings can have dirty bytes in them, resulting in the word-for-word comparisons giving incorrect results. Even without dirty nonzero bytes, two bytestrings can compare to equal if one ends with "\x00" because there is no comparison of the length. A patch is available and expected to be part of the 0.3.2 release. There are currently no known workarounds.