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

Quick assessment

Affected
tempoxyz pympp
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

pympp 是一个用于机器支付协议（Machine Payments Protocol）的 Python SDK。在 0.9.1 版本之前，当服务器充当费用支付方（fee_payer）时，pympp 会使用 eth_abi 解码来验证调用数据（calldata），而该解码方式对尾部字节较为宽松。FeePayerPolicy 虽然限制了 gas_limit（≤ 200 万）和 max_fee_per_gas（≤ 100 Gwei），但并未检查调用数据的长度。Tempo 采用传统的调用数据 Gas 计价机制：每个非零字

CVSS 6.9 · Medium

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-63634

Vulnerability Information
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Vulnerability Title
pympp: Gas Draining with padding
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
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: CVE Program / CVE List V5
Vulnerability Type
输入验证不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
tempoxyz pympp < 0.9.1 -

II. Public POCs for CVE-2026-63634

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III. Intelligence Information for CVE-2026-63634

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Other References for CVE-2026-63634 (3)

IV. Related Vulnerabilities

Same weakness: CWE-20