pympp: Gas Draining with padding
- Exploited
- No known exploitation
- Fix
- Fixed in 0.9.1
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 0.9.1.
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 24/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
pympp, a Python SDK for the Machine Payments Protocol, has a flaw in how it validates transaction calldata when the server acts as the fee payer. An attacker can remotely, without logging in, append padding bytes that inflate gas costs so the server cosigns and broadcasts the transaction, draining its fee-payer wallet.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Unknown: No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity6.9/10CVSS 6.9
- No patch0/5No signal
What would change the score
- Would score about 69 if added to CISA KEV
- Would score about 64 if CISA's SSVC rates exploitation active
- Would score about 29 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 0.9.1.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- tempoxyz pympp
fixed in 0.9.1
Evidence 3
- Advisory
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-63634
Is CVE-2026-63634 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-63634?
pympp: before 0.9.1.Source: cve.now feed data
How do I fix CVE-2026-63634?
Upgrade to a fixed version: 0.9.1.Source: cve.now feed data