{"id":"CVE-2026-59694","summary":"Unbounded access list in mpp Tempo fee-payer inflates gas cost per payment","details":"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.\n\nWhen 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.\n\nAt 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.\n\nThis issue affects mpp: from 0.2.0 before 0.6.0.","aliases":["EEF-CVE-2026-59694","GHSA-qpxh-ff8m-c62v"],"modified":"2026-08-12T03:51:09.722686821Z","published":"2026-07-17T10:11:49.192Z","database_specific":{"unresolved_ranges":[{"extracted_events":[{"introduced":"d29d54e507918db00a5b65d90136b73166c017d7"},{"fixed":"5d6338e2334084c5f2a78cfcca474830733ed7e8"}],"source":"AFFECTED_FIELD"}],"cna_assigner":"EEF","cwe_ids":["CWE-1284"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59694.json"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-59694.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-59694"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59694.json"},{"type":"ADVISORY","url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-qpxh-ff8m-c62v"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-59694"},{"type":"FIX","url":"https://github.com/ZenHive/mpp/commit/5d6338e2334084c5f2a78cfcca474830733ed7e8"},{"type":"PACKAGE","url":"https://github.com/ZenHive/mpp"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/zenhive/mpp","events":[{"introduced":"7ca7538f05959a98e0e5e63e4bd949b4f362cf8d"},{"fixed":"422bcdd066d1457a93bf5e75fd55e71c5e0be961"},{"fixed":"5d6338e2334084c5f2a78cfcca474830733ed7e8"}],"database_specific":{"source":["DESCRIPTION","REFERENCES"],"extracted_events":[{"introduced":"0.2.0"},{"fixed":"0.6.0"}]}}],"versions":["v0.5.1","v0.4.0","v0.3.0","v0.2.0"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-59694.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}]}