# CVE-2026-63634: pympp: Gas Draining with padding

Status: published. Published: 2026-11-09. Updated: 2026-11-09.

pympp is a Python SDK for the Machine Payments Protocol. Prior to version 0.9.1, when the server acts as the fee_payer, pympp validates calldata using eth_abi decoding, which is lenient about trailing bytes. The FeePayerPolicy caps gas_limit (≤ 2 M) and max_fee_per_gas (≤ 100 Gwei) but does not check calldata length. Tempo uses legacy calldata gas pricing: 16 gas per non-zero byte. Appending N bytes of 0x01 padding inflates actual gas used by N × 16 while keeping gas_limit and max_fee_per_gas within policy caps. The server cosigns and broadcasts the padded transaction, draining its fee-payer wallet. This issue has been patched in version 0.9.1.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- tempoxyz / pympp: < 0.9.1 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 4.0: 6.9 (medium); 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; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-20

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/tempoxyz/pympp/security/advisories/GHSA-v858-xh7w-8jr5 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/tempoxyz/pympp/commit/57a750d0d980b8e6c3bea62a40b7621f176ff1f0 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/tempoxyz/pympp/releases/tag/v0.9.1 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-63634; retrieved 2026-11-09; source updated 2026-11-09

Revision: b7cfda8abd4dc40b902a22aa61c675a345d109a202b046f26d56986b90feba04

Canonical: https://y2.dev/cve/CVE-2026-63634

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