GHSA-QPXH-FF8M-C62V
Vulnerability from github – Published: 2026-09-25 21:45 – Updated: 2026-09-25 21:45Details
When 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.
Access list gas is charged intrinsically — before any opcode executes — regardless of whether the listed addresses are ever touched.
An 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.
At 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).
PoC
The PoC is provided below. It is configured to reproduce the attack on Tempo Moderate testnet within a Docker environment. Download the PoC and run:
unzip mpp_elixir_PoC.zip
cd mpp_elixir
docker build -t mpp-elixir-access-list .
docker run --rm mpp-elixir-access-list
There are more details in mpp_elixir/README.md
Impact
A 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.
{
"affected": [
{
"package": {
"ecosystem": "Hex",
"name": "mpp"
},
"ranges": [
{
"events": [
{
"introduced": "0.2.0"
},
{
"fixed": "0.6.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-20"
],
"github_reviewed": true,
"github_reviewed_at": "2026-09-25T21:45:16Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"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** \u2014 before any opcode executes \u2014 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 \u00d7 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 \u2014 a **7.4\u00d7 multiplier** \u2014 while staying within Bandit\u0027s 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.",
"id": "GHSA-qpxh-ff8m-c62v",
"modified": "2026-09-25T21:45:16Z",
"published": "2026-09-25T21:45:16Z",
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"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",
"type": "CVSS_V4"
}
],
"summary": "mpp vulnerable to Gas Draining with access list"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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