CVE-2026-63634
pympp: Gas Draining with padding
Description
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.
INFO
Published Date :
Nov. 9, 2026, 8:59 p.m.
Last Modified :
Nov. 9, 2026, 8:59 p.m.
Remotely Exploit :
No
Source :
GitHub_M
Affected Products
The following products are affected by CVE-2026-63634
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
Solution
- Update pympp to version 0.9.1 or later.
- Validate calldata length strictly before processing.
- Implement gas usage checks based on actual calldata.
- Review fee payer gas policies for padding vulnerabilities.
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CVE-2026-63634 vulnerability anywhere in the article.