{"id":"GHSA-qpxh-ff8m-c62v","summary":"mpp vulnerable to Gas Draining with access list","details":"### Details\nWhen the server acts as the fee_payer, `mpp` Elixir 0.4.0 copies the client-supplied EIP-2930 access list verbatim into the cosigned fee-payer transaction. In `cosign_fee_payer`, the server re-signs the raw `base_fields` (index 5 of the 0x76 AASigned envelope) without inspecting the access list field, which is part of the signed payload.\n\nAccess list gas is charged **intrinsically** — before any opcode executes — regardless of whether the listed addresses are ever touched.\n\nAn attacker submits a valid `transferWithMemo` alongside fabricated address-only access list entries. The server validates calldata and amount but never inspects `access_list` length. It cosigns and broadcasts a transaction that costs the fee-payer wallet `N × 2,400` extra gas per request with no corresponding work performed on-chain.\n\nAt the default of 137 entries and 100 Gwei `max_fee_per_gas`, this inflates the fee-payer cost from the normal ~51,287 gas to ~380,087 gas — a **7.4× multiplier** — while staying within Bandit's default 10,000-byte per-header-field limit (verified empirically).\n\n### PoC\nThe PoC is provided below. It is configured to reproduce the attack on Tempo Moderate testnet within a Docker environment. Download the PoC and run:\n```bash\nunzip mpp_elixir_PoC.zip\ncd mpp_elixir\ndocker build -t mpp-elixir-access-list .\ndocker run --rm mpp-elixir-access-list\n``` \nThere are more details in `mpp_elixir/README.md`\n\n### Impact\nA malicious client can force the server to pay ~**7.4x** the normal transaction fee. This dramatically increases operational costs and completely destroys the profit margin on low-cost items.","aliases":["CVE-2026-59694","EEF-CVE-2026-59694"],"modified":"2026-09-25T23:00:39.698518550Z","published":"2026-09-25T21:45:16Z","database_specific":{"severity":"MODERATE","github_reviewed":true,"github_reviewed_at":"2026-09-25T21:45:16Z","nvd_published_at":null,"cwe_ids":["CWE-20"]},"references":[{"type":"WEB","url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-qpxh-ff8m-c62v"},{"type":"WEB","url":"https://github.com/ZenHive/mpp/commit/5d6338e2334084c5f2a78cfcca474830733ed7e8"},{"type":"PACKAGE","url":"https://github.com/ZenHive/mpp"},{"type":"WEB","url":"https://github.com/ZenHive/mpp/releases/tag/v0.6.0"}],"affected":[{"package":{"name":"mpp","ecosystem":"Hex","purl":"pkg:hex/mpp"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0.2.0"},{"fixed":"0.6.0"}]}],"versions":["0.2.0","0.3.0","0.3.1","0.3.2","0.4.0"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-qpxh-ff8m-c62v/GHSA-qpxh-ff8m-c62v.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N"}]}