tempoxyz pympp up to 0.9.0 FeePayerPolicy input validation

Summaryinfo

A vulnerability was found in tempoxyz pympp up to 0.9.0. It has been classified as problematic. Affected by this vulnerability is an unknown functionality of the component FeePayerPolicy. Performing a manipulation results in input validation. This vulnerability is cataloged as CVE-2026-63634. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as problematic, was found in tempoxyz pympp up to 0.9.0. This affects an unknown code block of the component FeePayerPolicy. The manipulation with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. This is going to have an impact on integrity. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-63634 since 07/17/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Neither technical details nor an exploit are publicly available.

Upgrading to version 0.9.1 eliminates this vulnerability.

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Productinfo

Vendor

• tempoxyz

Name

• pympp

Version

• 0.1
• 0.2
• 0.3
• 0.4
• 0.5
• 0.6
• 0.7
• 0.8
• 0.9.0

Website

• Product: https://github.com/tempoxyz/pympp/

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