CVE-2026-63634

What it 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.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-07-17 14:11 UTC ReservedThe CVE id was reserved by its CNA
2. 2026-11-09 20:59 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2026-11-09 20:59 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: not scored yet.
• Severity: 6.9 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-11-09 20:59 UTC

Last modified

2026-11-09 20:59 UTC

Weakness

CWE-20 · Improper input validation

Record status

Received

Affected

• Tempoxyz Pympp < 0.9.1

Attack profile CVSS 4.0 · 6.9

Attack vector

Network

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

None

Confidentiality

None

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-63634.md and follow it. Check whether this project is affected by CVE-2026-63634. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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