Summary

Terrapin is a prefix truncation attack targeting the SSH protocol. More precisely, Terrapin breaks the integrity of SSH's secure channel. By carefully adjusting the sequence numbers during the handshake, an attacker can remove an arbitrary amount of messages sent by the client or server at the beginning of the secure channel without the client or server noticing it.

Mitigations

To mitigate this protocol vulnerability, OpenSSH suggested a so-called "strict kex" which alters the SSH handshake to ensure a Man-in-the-Middle attacker cannot introduce unauthenticated messages as well as convey sequence number manipulation across handshakes.

Warning: To take effect, both the client and server must support this countermeasure.

As a stop-gap measure, peers may also (temporarily) disable the affected algorithms and use unaffected alternatives like AES-GCM instead until patches are available.

Details

The SSH specifications of ChaCha20-Poly1305 (chacha20-poly1305@openssh.com) and Encrypt-then-MAC (-etm@openssh.com MACs) are vulnerable against an arbitrary prefix truncation attack (a.k.a. Terrapin attack). This allows for an extension negotiation downgrade by stripping the SSHMSGEXTINFO sent after the first message after SSHMSGNEWKEYS, downgrading security, and disabling attack countermeasures in some versions of OpenSSH. When targeting Encrypt-then-MAC, this attack requires the use of a CBC cipher to be practically exploitable due to the internal workings of the cipher mode. Additionally, this novel attack technique can be used to exploit previously unexploitable implementation flaws in a Man-in-the-Middle scenario.

The attack works by an attacker injecting an arbitrary number of SSHMSGIGNORE messages during the initial key exchange and consequently removing the same number of messages just after the initial key exchange has concluded. This is possible due to missing authentication of the excess SSHMSGIGNORE messages and the fact that the implicit sequence numbers used within the SSH protocol are only checked after the initial key exchange.

In the case of ChaCha20-Poly1305, the attack is guaranteed to work on every connection as this cipher does not maintain an internal state other than the message's sequence number. In the case of Encrypt-Then-MAC, practical exploitation requires the use of a CBC cipher; while theoretical integrity is broken for all ciphers when using this mode, message processing will fail at the application layer for CTR and stream ciphers.

For more details see https://terrapin-attack.com.

Impact

This attack targets the specification of ChaCha20-Poly1305 (chacha20-poly1305@openssh.com) and Encrypt-then-MAC (-etm@openssh.com), which are widely adopted by well-known SSH implementations and can be considered de-facto standard. These algorithms can be practically exploited; however, in the case of Encrypt-Then-MAC, we additionally require the use of a CBC cipher. As a consequence, this attack works against all well-behaving SSH implementations supporting either of those algorithms and can be used to downgrade (but not fully strip) connection security in case SSH extension negotiation (RFC8308) is supported. The attack may also enable attackers to exploit certain implementation flaws in a man-in-the-middle (MitM) scenario.

crypto: algifaead - Revert to operating out-of-place

A heap-buffer-overread vulnerability exists in GnuTLS (confirmed in version 3.8.9) due to unsafe handling of the Certificate Transparency (CT) Signed Certificate Timestamp (SCT) extension during X.509 certificate parsing. The vulnerability can be triggered by a malicious peer presenting a crafted certificate containing a malformed SCT extension (OID 1.3.6.1.4.1.11129.2.4.2). This overread may lead to disclosure of heap memory contents to attackers if the SCT logid is logged, exported, or otherwise exposed by the application consuming the GnuTLS client library.

A double-free vulnerability exists in GnuTLS (confirmed in version 3.8.9) due to incorrect ownership handling in the export logic of Subject Alternative Name (SAN) entries containing an otherName. If the type-id OID is invalid or malformed, GnuTLS will call asn1deletestructure() on an ASN.1 node it does not own, leading to a double-free condition when the parent function or caller later attempts to free the same structure. This vulnerability can be triggered using only public GnuTLS APIs and may result in denial of service or memory corruption, depending on allocator behavior.

A vulnerability was found in OpenSSH when the VerifyHostKeyDNS option is enabled. A machine-in-the-middle attack can be performed by a malicious machine impersonating a legit server. This issue occurs due to how OpenSSH mishandles error codes in specific conditions when verifying the host key. For an attack to be considered successful, the attacker needs to manage to exhaust the client's memory resource first, turning the attack complexity high.

A race condidition in systemd-coredump allows a local attacker to crash a SUID program and gain read access to the resulting core dump

A security regression (CVE-2006-5051) was discovered in OpenSSH's server (sshd). There is a race condition which can lead sshd to handle some signals in an unsafe manner. An unauthenticated, remote attacker may be able to trigger it by failing to authenticate within a set time period.

HTTP/2 Rapid reset attack The HTTP/2 protocol allows clients to indicate to the server that a previous stream should be canceled by sending a RSTSTREAM frame. The protocol does not require the client and server to coordinate the cancellation in any way, the client may do it unilaterally. The client may also assume that the cancellation will take effect immediately when the server receives the RSTSTREAM frame, before any other data from that TCP connection is processed.

Abuse of this feature is called a Rapid Reset attack because it relies on the ability for an endpoint to send a RSTSTREAM frame immediately after sending a request frame, which makes the other endpoint start working and then rapidly resets the request. The request is canceled, but leaves the HTTP/2 connection open.

The HTTP/2 Rapid Reset attack built on this capability is simple: The client opens a large number of streams at once as in the standard HTTP/2 attack, but rather than waiting for a response to each request stream from the server or proxy, the client cancels each request immediately.

The ability to reset streams immediately allows each connection to have an indefinite number of requests in flight. By explicitly canceling the requests, the attacker never exceeds the limit on the number of concurrent open streams. The number of in-flight requests is no longer dependent on the round-trip time (RTT), but only on the available network bandwidth.

In a typical HTTP/2 server implementation, the server will still have to do significant amounts of work for canceled requests, such as allocating new stream data structures, parsing the query and doing header decompression, and mapping the URL to a resource. For reverse proxy implementations, the request may be proxied to the backend server before the RSTSTREAM frame is processed. The client on the other hand paid almost no costs for sending the requests. This creates an exploitable cost asymmetry between the server and the client.

Multiple software artifacts implementing HTTP/2 are affected. This advisory was originally ingested from the swift-nio-http2 repo advisory and their original conent follows.

swift-nio-http2 specific advisory swift-nio-http2 is vulnerable to a denial-of-service vulnerability in which a malicious client can create and then reset a large number of HTTP/2 streams in a short period of time. This causes swift-nio-http2 to commit to a large amount of expensive work which it then throws away, including creating entirely new Channels to serve the traffic. This can easily overwhelm an EventLoop and prevent it from making forward progress.

swift-nio-http2 1.28 contains a remediation for this issue that applies reset counter using a sliding window. This constrains the number of stream resets that may occur in a given window of time. Clients violating this limit will have their connections torn down. This allows clients to continue to cancel streams for legitimate reasons, while constraining malicious actors.

A flaw was found in libarchive. On 32-bit systems, an integer overflow vulnerability exists in the zisofs block pointer allocation logic. A remote attacker can exploit this by providing a specially crafted ISO9660 image, which can lead to a heap buffer overflow. This could potentially allow for arbitrary code execution on the affected system.

A flaw was found in libcap. A local unprivileged user can exploit a Time-of-check-to-time-of-use (TOCTOU) race condition in the capsetfile() function. This allows an attacker with write access to a parent directory to redirect file capability updates to an attacker-controlled file. By doing so, capabilities can be injected into or stripped from unintended executables, leading to privilege escalation.

A flaw was found in libarchive. This heap out-of-bounds read vulnerability exists in the RAR archive processing logic due to improper validation of the LZSS sliding window size after transitions between compression methods. A remote attacker can exploit this by providing a specially crafted RAR archive, leading to the disclosure of sensitive heap memory information without requiring authentication or user interaction.

A flaw was found in libsolv. This heap buffer overflow occurs during the decompression of attacker-controlled compressed data within .solv files due to insufficient input validation. An attacker can provide a specially crafted .solv file, which, when processed by a vulnerable application, can lead to out-of-bounds memory access. This could result in information disclosure, alteration of program execution, or a denial of service.

A flaw was found in gnutls. Servers configured with RSA-PSK (Rivest–Shamir–Adleman – Pre-Shared Key) wrongfully matched usernames containing a NUL character with truncated usernames. A remote attacker could exploit this by sending a specially crafted username, leading to an authentication bypass. This vulnerability allows an attacker to gain unauthorized access by circumventing the authentication process.

A flaw was found in gnutls. A remote attacker could exploit an issue in the Datagram Transport Layer Security (DTLS) packet reordering logic. The comparator function, responsible for ordering DTLS packets by sequence numbers, did not correctly handle packets with duplicate sequence numbers. This could lead to unstable packet ordering or undefined behavior, resulting in a denial of service.

A flaw was found in gnutls. A remote attacker could exploit this vulnerability by presenting a specially crafted Online Certificate Status Protocol (OCSP) response during a TLS handshake. Due to a logic error in how gnutls processes multi-record OCSP responses, a client with OCSP verification enabled may incorrectly accept a revoked server certificate, potentially leading to a compromise of trust.

A flaw was found in gnutls. This vulnerability occurs because gnutls performs case-sensitive comparisons of nameConstraints labels, specifically for dNSName (DNS) or rfc822Name (email) constraints within excludedSubtrees or permittedSubtrees. A remote attacker can exploit this by crafting a leaf certificate with casing differences in the Subject Alternative Name (SAN), leading to a policy bypass where a certificate that should be rejected is instead accepted. This could result in unauthorized access or information disclosure.

A flaw in GnuTLS DTLS handshake parsing allows malformed fragments with zero length and non-zero offset, leading to an integer underflow during reassembly and resulting in an out-of-bounds read. This issue is remotely exploitable and may cause information disclosure or denial of service.

A flaw was found in the interactive shell of the xmllint command-line tool, used for parsing XML files. When a user inputs an overly long command, the program does not check the input size properly, which can cause it to crash. This issue might allow attackers to run harmful code in rare configurations without modern protections.

A flaw was found in Samba’s vfsworm module. The module is intended to provide write-once, read-many (WORM) protections by preventing modification of files after a configurable grace period. Due to insufficient validation during rename operations, an authenticated user with write access to a share could overwrite a protected file by renaming a newly created file over the existing WORM-protected file.

A flaw was found in p11-kit. The RPC message attribute parsing functions p11rpcmessagegetattribute() and p11rpcmessagegetattributearrayvalue() form a mutually-recursive call chain with no recursion depth limit when processing nested CKAWRAPTEMPLATE, CKAUNWRAPTEMPLATE, and CKADERIVETEMPLATE attributes. An unauthenticated attacker with local access to the p11-kit RPC Unix domain socket can send a specially crafted request with deeply nested template attributes, causing stack exhaustion and crashing the p11-kit server process and its dependent services.

A heap use-after-free vulnerability was found in systemd before version v245-rc1, where asynchronous Polkit queries are performed while handling dbus messages. A local unprivileged attacker can abuse this flaw to crash systemd services or potentially execute code and elevate their privileges, by sending specially crafted dbus messages.

A flaw was found in OpenSSH. A malicious SSH server can exploit a double free vulnerability in the Diffie-Hellman Group Exchange (DH-GEX) client path. This occurs during FIPS (Federal Information Processing Standards) mode known-group validation when the client processes attacker-controlled DH-GEX group parameters. Successful exploitation leads to client-side process termination, resulting in a Denial of Service (DoS).

A vulnerability was found in Python 2.7.x through 2.7.16 and 3.x through 3.7.2. An improper Handling of Unicode Encoding (with an incorrect netloc) during NFKC normalization could lead to an Information Disclosure (credentials, cookies, etc. that are cached against a given hostname) in the urllib.parse.urlsplit, urllib.parse.urlparse components. A specially crafted URL could be incorrectly parsed to locate cookies or authentication data and send that information to a different host than when parsed correctly.

References: https://bugs.python.org/issue36216 https://python-security.readthedocs.io/vuln/urlsplit-nfkc-normalization.html

Uptream Patch: https://github.com/python/cpython/pull/12201

A flaw was found in the Windows Machine Config Operator (WMCO) for Red Hat OpenShift Container Platform. WMCO establishes SSH connections to Windows worker nodes without verifying the remote server host key. An adjacent-network attacker who can intercept or redirect WMCO's SSH session can capture WICD and kubelet bootstrap credentials transferred during node configuration, enabling compromise of Windows node identities in the cluster.

A flaw was found in the Windows Machine Config Operator (WMCO) for Red Hat OpenShift Container Platform. The WICD CSR auto-approver validates that a Certificate Signing Request contains the organization system:wicd-nodes but does not reject additional organization values such as system:masters. A compromised Windows worker node that holds WICD credentials can submit a CSR that is auto-approved and signed by the cluster, yielding a client certificate that grants cluster-administrator privileges and enabling full cluster takeover.

This is a vulnerability report sent to us through https://issues.redhat.com/browse/PSIRTSUPT-17918 and was created using the PoC auto-triage agents. It contains hints on the vulnerability extracted by the IA and the full report. ALWAYS review it before any action. Once working on this, don't forget to also update the JSM ticket.

Multiple Use-After-Free vulnerabilities were found in the addarchiveelement function in ld/ldmain.c of the GNU linker (ld), a component of binutils. The root cause is that pluginmaybeclaim() in ld/plugin.c frees the original BFD object via bfdclose/bfddeletebfd when entry->thebfd->myarchive == NULL, but the caller retains both the original abfd parameter and a shallow copy (originput.thebfd) as dangling pointers. These dangling pointers are subsequently dereferenced at three distinct locations in addarchiveelement:

1. Line ~1442: accessing abfd->myarchive via bfdusrdata(abfd->myarchive) 2. Line ~1493: multiple accesses to abfd and abfd->myarchive in a conditional check and bfdgetfilename call 3. Line ~1525: dereferencing the shallow copy originput.thebfd->myarchive in trace/verbose logging

The vulnerability is triggered when LTO plugins are active (linkinfo.ltopluginactive is true) and the input object has abfd->myarchive == NULL, which is a valid state for standalone object files. Red Hat builds binutils with --enable-plugins and --enable-lto, confirming the vulnerable code path is compiled in and reachable.

An attacker who can supply a crafted object or archive file to a build process using LTO-enabled linking could exploit this flaw to cause a denial of service (linker crash via segmentation fault). Arbitrary code execution is theoretically possible through heap manipulation but is substantially mitigated by hardening measures including stack protector, FORTIFYSOURCE, ASLR, and PIE.

The attack surface is limited to build-time environments — the linker is a development tool not exposed in production runtime. The most realistic exploitation scenario is a supply chain attack introducing a crafted object file as a build dependency in CI/CD pipelines or development environments.

A flaw was found in SSSD. A local user can trigger a Denial of Service (DoS) by exploiting a race condition in the autofs responder between asynchronous enumeration completion and map invalidation. By repeatedly sending concurrent map enumeration and invalidation requests, an attacker can cause memory to leak, leading to excessive memory consumption that can disrupt or crash the autofs service.

A flaw was found in SSSD (System Security Services Daemon). When Identity Provider (IdP) authentication is enabled, pre-authentication requests retain state in memory without being cleared or timed out. A local attacker can repeatedly initiate authentication flows without completing them, causing unbounded memory consumption. This memory exhaustion can lead to a Denial of Service (DoS) by degrading or terminating SSSD authentication services.

A flaw in the containers/common Go library, used by container runtimes such as Podman, Buildah, and CRI-O, allows a malicious container image to exploit the FIPS mode to bind mount arbitrary host directories into the container. The flaw arises from the MountsWithUIDGID() function, which attempts to mount a FIPS-related directory inside the container but does not properly verify the path. If the FIPS path is a symlink, it could point to arbitrary directories on the host, allowing an attacker to access sensitive host files.

A flaw was found in rsync which could be triggered when rsync compares file checksums. This flaw allows an attacker to manipulate the checksum length (s2length) to cause a comparison between a checksum and uninitialized memory and leak one byte of uninitialized stack data at a time.