{"id":"GHSA-qpxh-ff8m-c62v","title":"mpp vulnerable to Gas Draining with access list","summary":"mpp vulnerable to Gas Draining with access list","severity":"medium","cwe":["CWE-20"],"vendor":"mpp","product":"mpp","ecosystem":"erlang","affected":["mpp >= 0.2.0, < 0.6.0"],"patched":["mpp 0.6.0"],"published":"2026-09-25","updated":"2026-09-25","sourceUpdated":"2026-09-25T21:45:26Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-qpxh-ff8m-c62v","references":[{"url":"https://github.com/ZenHive/mpp/security/advisories/GHSA-qpxh-ff8m-c62v"},{"url":"https://github.com/ZenHive/mpp/commit/5d6338e2334084c5f2a78cfcca474830733ed7e8"},{"url":"https://github.com/ZenHive/mpp/releases/tag/v0.6.0"},{"url":"https://github.com/advisories/GHSA-qpxh-ff8m-c62v"}],"tags":["ghsa","erlang"],"ingestedAt":"2026-09-25T22:20:31.566Z","slug":"GHSA-qpxh-ff8m-c62v","body":"## Overview\n\n### 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.\n\n## Affected packages\n\n- `mpp >= 0.2.0, < 0.6.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `mpp 0.6.0`","depth":"sunlit","depthScore":28,"depthScoreParts":{"impact":27.5,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}