Unbounded access list in mpp Tempo fee-payer inflates gas cost per payment

{
  "id": "748ebd3c110c765c1cfc3902ed84b4338fbfbde3e77f658a63890d9f2aa0acdc",
  "url": "https://osv.dev/vulnerability/CVE-2026-59694",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Unbounded access list in mpp Tempo fee-payer inflates gas cost per payment",
    "summary": "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.",
    "evidence": "osv:CVE-2026-59694",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-59694",
      "aliases": [
        "CVE-2026-59694",
        "EEF-CVE-2026-59694",
        "GHSA-qpxh-ff8m-c62v"
      ],
      "metrics": [
        {
          "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"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/zenhive/mpp",
              "type": "GIT",
              "events": [
                {
                  "introduced": "7ca7538f05959a98e0e5e63e4bd949b4f362cf8d"
                },
                {
                  "fixed": "422bcdd066d1457a93bf5e75fd55e71c5e0be961"
                },
                {
                  "fixed": "5d6338e2334084c5f2a78cfcca474830733ed7e8"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0.2.0"
                      },
                      {
                        "fixed": "0.6.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "fixed": "5d6338e2334084c5f2a78cfcca474830733ed7e8"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "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"
          }
        }
      ],
      "modified": "2026-10-28T02:30:22.493209922Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-59694.html",
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-59694",
        "https://repo.hex.pm",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59694.json",
        "https://github.com/ZenHive/mpp/security/advisories/GHSA-qpxh-ff8m-c62v",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-59694",
        "https://github.com/ZenHive/mpp/commit/5d6338e2334084c5f2a78cfcca474830733ed7e8",
        "https://github.com/ZenHive/mpp"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-1284"
        ],
        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59694.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-59694",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 488839,
  "published_at": "2026-07-17T10:11:49.192+00:00"
}