CVE-2026-59695

Description

Improper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated remote client to drain the fee-payer wallet in a single request by naming an arbitrarily high gas price. 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 max_fee_per_gas and max_priority_fee_per_gas, without validating that they are within reasonable bounds. A malicious client embeds arbitrarily large values for these fields in the signed envelope. The server co-signs and broadcasts the transaction. The effective_gas_price billed against the fee-payer wallet is derived from the attacker-supplied ceilings, so the server pays those inflated per-gas rates out of its own wallet. A single crafted request can drain the wallet entirely, after which the server can no longer sponsor gas for legitimate payment requests. This issue affects mpp: from 0.2.0 before 0.6.0.

Severity (CVSS)

Weaknesses

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

Affected products

References

• https://github.com/ZenHive/mpp/security/advisories/GHSA-vv77-66rf-pm86 (vendor-advisory related)
• https://cna.erlef.org/cves/CVE-2026-59695.html (related)
• https://osv.dev/vulnerability/EEF-CVE-2026-59695 (related)
• https://github.com/ZenHive/mpp/commit/5d6338e2334084c5f2a78cfcca474830733ed7e8 (patch)