EUVD-2026-45159
GHSA-r4hx-mhrp-xf73
Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Unauthenticated network access to a fee-payer deployment (PR:N, AV:N, AC:L); no confidentiality or data-integrity impact; sustained gas/wallet drain is a resource-exhaustion availability impact (A:H).
Primary rating from Vendor (EEF).
CVSS VectorVendor: EEF
Lifecycle Timeline
3DescriptionCVE.org
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.
AnalysisAI
Economic resource exhaustion in the ZenHive mpp Elixir library (versions 0.2.0 through 0.5.x) lets an unauthenticated remote client inflate a sponsoring fee-payer's gas cost per payment by roughly 7.4x, draining the sponsor wallet over sustained abuse. When deployed with fee_payer: true, MPP.Tempo.Transaction.cosign_fee_payer/3 re-signs client-supplied base fields of the 0x76 AASigned envelope verbatim - including an oversized EIP-2930 access list - without validating length or contents, so intrinsic gas is charged for fabricated entries that touch nothing on-chain. No public exploit identified at time of analysis, but the attack is fully detailed in the vendor advisory and fixed in 0.6.0.
Technical ContextAI
The affected component is the Tempo transaction-sponsorship path of the mpp Elixir library (cpe:2.3:a:zenhive:mpp), used to let a server pay gas on behalf of clients for account-abstraction-style payments. The vulnerability is CWE-1284 (Improper Validation of Specified Quantity in Input): the server co-signs the client's 0x76 AASigned envelope without bounding the EIP-2930 access list. EIP-2930 access lists charge intrinsic gas up front - about 2,400 gas per listed address and 1,900 gas per storage key - billed before any opcode runs and regardless of whether those addresses are ever accessed. Because cosign_fee_payer/3 trusts the client-signed base fields verbatim, an attacker's padded access list is paid for entirely by the fee-payer wallet.
RemediationAI
Upgrade to mpp 0.6.0, which is the vendor-released patch (commit 5d6338e2334084c5f2a78cfcca474830733ed7e8) that adds MPP.Methods.Tempo.FeePayerPolicy to validate the client-signed 0x76 envelope's gas economics before co-signing - bounding gas_limit, max_fee_per_gas, max_priority_fee_per_gas, and the total-fee budget, and rejecting non-empty access lists; the fix is safe-by-default so existing fee_payer: true deployments are protected without config changes, and it also closes the related unbounded-fee vector GHSA-vv77-66rf-pm86. If immediate upgrade is not possible, the most direct compensating control is to disable fee-payer sponsorship (set fee_payer: false), which eliminates the drain entirely but removes the gas-sponsorship feature; alternatively, front the endpoint with a proxy that rejects requests carrying a non-empty EIP-2930 access list or an oversized 0x76 header (the maintainer notes 137 entries fit within Bandit's 10,000-byte per-header-field limit, so tightening that limit reduces but does not eliminate the multiplier). See the advisory at https://github.com/ZenHive/mpp/security/advisories/GHSA-qpxh-ff8m-c62v. Note the separately tracked low-gas-limit revert vector (GHSA-vj8p-hp9x-gh47) is not addressed by this patch.
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