GHSA-vv77-66rf-pm86: Input Validation
Details When the server acts as the feepayer, the mpp Elixir 0.4.0 does not validate gaslimit, maxfeepergas and maxpriorityfeepergas before cosigning the client's fee-payer transaction. A malicious client embeds arbitrarily large maxfeepergas and maxpriorityfeepergas values in the signed envelope. The server cosigns and broadcasts — paying those inflated gas costs from its own wallet based on the effectivegasprice calculated from the high maxfeepergas and maxpriorityfeepergas set by the client.
Vulnerable function: cosignfeepayer/3 in transaction.ex around lines 229–262.
PoC The PoC is provided below. It is configured to reproduce the attack on Tempo Moderate testnet within a Docker environment. Download the PoC and run: bash unzip mppelixirPoC.zip cd mppelixir docker build -t mpp-elixir-gasdrain . docker run --rm mpp-elixir-gasdrain There are more details in mppelixir/README.md
Impact By draining the server's wallet, an attacker causes direct financial loss to the organization. Furthermore, if the server's funds are drained completely, legitimate clients will have their requests fail, as the server can no longer fund future transactions, effectively creating a Denial of Service (DoS) attack.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
erlang/mppto a version that resolves this vulnerability.Fixed in 0.6.0
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Deployments in which the server acts as the fee payer are exposed. The issue affects the server-side fee-payer cosigning path in mpp Elixir 0.4.0.
What does an attacker need to exploit it?
An attacker needs to submit a fee-payer transaction for the server to cosign. They can place arbitrarily large max_fee_per_gas and max_priority_fee_per_gas values in the signed envelope.
What is the practical impact of successful exploitation?
The server can broadcast the transaction and pay inflated gas costs from its own wallet. Repeated exploitation can drain the wallet, causing direct financial loss and potentially preventing legitimate clients from using the service.
What code path should be reviewed or remediated?
Review the cosign_fee_payer/3 function in transaction.ex, identified around lines 229–262 in mpp Elixir 0.4.0. The required control is validation of gas_limit, max_fee_per_gas, and max_priority_fee_per_gas before the server cosigns the transaction.