CVE-2026-59694
HighCVSS 8.3Exploitation Probability (EPSS)
Low risk22th percentile - higher than 22% of all known CVEs
Summary
A vulnerability in the mpp library (ZenHive) allows an unauthenticated remote client to inflate the fee-payer's gas cost by adding a large number of fabricated EIP-2930 access list entries. The server co-signs the transaction without validating the list length or contents, leading to a multiple increase in gas costs.
Risk Assessment
The organization faces the risk of significantly increased operational costs – an attacker can multiply gas fees (up to 7.4x), eroding the sponsor's operating margin on low-cost payments and eventually draining the fee-payer wallet.
Recommendation
Immediately upgrade the mpp library to version 0.6.0 or later, which includes a fix for validating the EIP-2930 access list. As a temporary measure, enforce a maximum number of access list entries at the application level.
Other vulnerabilities in mpp
See all- CVE-2026-59695High
A vulnerability in the ZenHive mpp library allows an unauthenticated remote attacker to drain the fee-payer wallet in a single request by specifying an arbitrarily high gas price. The library does not validate the max_fee_per_gas and max_priority_fee_per_gas fields before co-signing the transaction, causing the server's wallet to be charged inflated costs.
- CVE-2026-59252High
A vulnerability in the mpp library (ZenHive) allows an unauthenticated remote client to drain the fee-payer wallet by submitting EVM transactions with a deliberately low gas limit. The server co-signs and broadcasts the transaction, which fails due to out-of-gas, but the fee-payer wallet is charged for the burned gas while the attacker pays nothing. This leads to denial of service for legitimate clients as the fee-payer wallet runs out of funds.
Original NVD description (English source)
Improper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated remote client to inflate the fee-payer's gas cost per payment by a large multiplier, degrading the sponsor's operating margin. When the mpp Elixir library is configured as fee payer (fee_payer: true), MPP.Tempo.Transaction.cosign_fee_payer/3 re-signs the client-supplied base fields of the 0x76 AASigned envelope verbatim, including the EIP-2930 access list, without validating its length or contents. EIP-2930 access list entries incur intrinsic gas (~2,400 gas per address, plus 1,900 gas per storage key) charged before any opcode executes, regardless of whether the listed addresses are ever touched. A malicious client submits a valid transferWithMemo call alongside a large number of fabricated access-list entries. The server co-signs and broadcasts the transaction. The intended transfer executes normally, but the fee-payer wallet pays a large multiple of the expected gas cost with no corresponding on-chain work. At the maintainer's default of 137 access-list entries (fitting within Bandit's 10,000-byte per-header-field limit) and 100 Gwei max_fee_per_gas, per-payment gas cost rises from ~51,287 to ~380,087 gas, a 7.4x multiplier. Sustained abuse destroys the sponsor's operating margin on low-cost payments and, over time, drains the fee-payer wallet. This issue affects mpp: from 0.2.0 before 0.6.0.