# CVE-2026-59694: ZenHive mpp gas cost inflation via unvalidated access list

Source: https://junglewise.ai/threats/cve-2026-59694-zenhive-mpp-gas-cost-inflation-via-unvalidated-access-list  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-17. Updated: 2026-07-17  
License: CC BY 4.0 with a link back

CVE-2026-59694 · Severity: info · CVSS 8.3 · Published 2026-07-17

ZenHive mpp is an Elixir library used for processing blockchain payments. A vulnerability exists where the library fails to validate certain transaction data when configured to pay for user transaction fees. An attacker can exploit this to force the service provider to pay significantly higher transaction fees than necessary, potentially draining the provider's digital wallet and destroying their operating margins.

Technologies: [ZenHive Mpp](https://junglewise.ai/threats/technologies/mpp). Vendors: [ZenHive](https://junglewise.ai/threats/vendors/zenhive).

## Quick answers

**Is CVE-2026-59694 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-59694 being exploited in the wild.

**How severe is CVE-2026-59694?** Informational severity, with a CVSS score of 8.3, published 17 July 2026.

**Which products and versions are affected?** ZenHive Mpp from 0.2.0 before 0.6.0.

**Is there a fix for CVE-2026-59694?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-59694 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-59694?** Check whether you run ZenHive Mpp at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in the `MPP.Tempo.Transaction.cosign_fee_payer/3` function when `fee_payer` is set to true. The library re-signs client-supplied base fields of the 0x76 AASigned envelope verbatim, including the EIP-2930 access list, without validating its length or content. Because access list entries incur intrinsic gas costs charged before execution, an attacker can include a large number of fabricated entries. This results in the fee-payer wallet paying a large multiple of the expected gas cost (up to 7.4x in tested scenarios) for transactions that perform no additional on-chain work. The issue is fixed in version 0.6.0.

## Affected products

- ZenHive mpp from 0.2.0 before 0.6.0

## Timeline

- 2026-06-24: advisory: GitHub Security Advisory GHSA-qpxh-ff8m-c62v published
- 2026-07-17: disclosed: CVE-2026-59694 published to NVD

## References

- [https://repo.hex.pm/](https://repo.hex.pm/)
- [https://github.com/](https://github.com/)
- [https://cna.erlef.org/cves/CVE-2026-59694.html](https://cna.erlef.org/cves/CVE-2026-59694.html)
- [https://github.com/ZenHive/mpp/commit/5d6338e2334084c5f2a78cfcca474830733ed7e8](https://github.com/ZenHive/mpp/commit/5d6338e2334084c5f2a78cfcca474830733ed7e8)
- [https://github.com/ZenHive/mpp/security/advisories/GHSA-qpxh-ff8m-c62v](https://github.com/ZenHive/mpp/security/advisories/GHSA-qpxh-ff8m-c62v)

## Related threats

- [mpp gas limit validation failure in broadcast_and_verify](https://junglewise.ai/threats/mpp-vulnerable-to-gas-draining-with-low-gas-limit-9a9ae054)
- [ZenHive mpp input validation bypass in fee-payer cosigning](https://junglewise.ai/threats/mpp-vulnerable-to-gas-draining-with-no-limit-9bf9cd33)
- [ZenHive mpp authorization bypass in payment channel validation](https://junglewise.ai/threats/cve-2026-89420-improper-validation-of-specified-quantity-in-input-in-zenhive-mpp)
- [ZenHive mpp authentication bypass in subscription activation](https://junglewise.ai/threats/cve-2026-87119-authentication-bypass-by-capture-replay-in-zenhive-mpp-allows-an)
- [ZenHive mpp HTTP cache header override vulnerability](https://junglewise.ai/threats/cve-2026-89186-zenhive-mpp-http-cache-header-override-vulnerability)