Weakness Type (CWE)

CWE-1284 — CWE-1284 Improper Validation of Specified Quantity in Input

CAPEC

CVSS 4.0 Score

8.3

HIGH

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

Vulnerability description

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.

Affected

pkg:hex/mpp

Module Source File Routine
MPP.Tempo.Transaction lib/mpp/tempo/transaction.ex MPP.Tempo.Transaction.cosign_fee_payer/3
Status Type Version Changes / Fixed in
affected semver ⓘ 0.2.0 < 0.6.0

pkg:github/ZenHive/mpp

Module Source File Routine
MPP.Tempo.Transaction lib/mpp/tempo/transaction.ex MPP.Tempo.Transaction.cosign_fee_payer/3
Status Type Version Changes / Fixed in
affected git ⓘ d29d54e507 < 5d6338e233

Configurations

The vulnerable code path is only reachable when the MPP.Methods.Tempo method is configured with fee_payer: true (server-side gas sponsorship). Default deployments with fee_payer: false are not affected, since the client pays for gas out of its own wallet.

References

Credits

  • Finder: Kian Kai Ang
  • Remediation developer: E.FU
  • Analyst: Jonatan Männchen / EEF

CVE record as JSON:  GET /cves/CVE-2026-59694.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-59694.json