CVE-2026-63627 mppx: Gas Draining with padding
Attackers can inflate transaction fees paid by the server wallet by appending padding to calldata, causing financial loss and resource exhaustion.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63627?
CVE-2026-63627 is a medium-severity vulnerability in wevm mppx, published on 22 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
mppx is a TypeScript interface for machine payments protocol. Prior to 0.8.2, FeePayerPolicy in src/tempo/internal/fee-payer.ts used decodeFunctionData to validate fee-sponsored calldata but did not reject trailing bytes. A client could append nonzero padding that increased intrinsic calldata gas while gas_limit and max_fee_per_gas remained within policy caps, causing the server fee_payer wallet to pay substantially more than the decoded transaction required. The tested 16 KB header limit bounded the demonstrated padding to about 5,500 bytes and produced approximately five times the normal transaction fee. This issue is fixed in version 0.8.2.
Weakness: CWE-20
Which versions are affected by CVE-2026-63627?
2 open source packages ship an affected version, including mppx.
| Package | Affected | Fixed in |
|---|---|---|
mppx npm | All versions | 0.8.2 |
mppx npm | All versions | 0.8.2 |
How do I fix CVE-2026-63627?
Upgrade mppx to 0.8.2 or later.
Is CVE-2026-63627 being exploited?
There is no known exploitation of CVE-2026-63627 in the wild and no public exploit code.
Sources
Also known as GHSA-727h-3vm5-qwq6.