How severe is GHSA-727h-3vm5-qwq6?

No CVSS score has been assigned to GHSA-727h-3vm5-qwq6 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by GHSA-727h-3vm5-qwq6?

GHSA-727h-3vm5-qwq6 affects the following packages: mppx (npm). Ecosystems affected: npm.

How do I fix GHSA-727h-3vm5-qwq6?

Update mppx to 0.8.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-727h-3vm5-qwq6 is resolved across your whole dependency graph.

How do I detect GHSA-727h-3vm5-qwq6 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mppx, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-727h-3vm5-qwq6 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is GHSA-727h-3vm5-qwq6 actively exploited in the wild?

No public exploit code has been indexed for GHSA-727h-3vm5-qwq6 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-727h-3vm5-qwq6?

GHSA-727h-3vm5-qwq6 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 31th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-727h-3vm5-qwq6?

GHSA-727h-3vm5-qwq6 is classified as Improper Input Validation (CWE-20). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-727h-3vm5-qwq6 published, and has it been updated?

GHSA-727h-3vm5-qwq6 was published on September 22, 2026 and was last updated on September 22, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

mppx: Gas Draining with paddingGHSA-727h-3vm5-qwq6

Fix: wevm/mppx#602

GHSA-727h-3vm5-qwq6 is a Improper Input Validation vulnerability in mppx. A fix is available for mppx — see the affected versions and patch details below.

Also known asCVE-2026-63627

Published

Sep 22, 2026

Updated

Sep 22, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-727h-3vm5-qwq6.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs31th percentile — riskier than 31% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

137other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

mppxnpm

153Kdownloads / week

Description

Details

When the server acts as the fee_payer, mppx 0.6.27 validates calldata using viem's decodeFunctionData, 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.

Vulnerable code path: FeePayerPolicy in fee-payer.ts (mppx 0.6.27) enforces maxGas = 2_000_000 and maxFeePerGas = 100 Gwei but has no calldata.length bound. The policy check passes because the inflated gas comes from intrinsic calldata cost, not the declared gas_limit.

Note: In the experiment, a 16 KB max_header_length is enforced, which caps the maximum effective padding at roughly 5,500 bytes. The default padding in this PoC (5,500 bytes) is within that limit.

PoC

The PoC is provided below. It is configured to reproduce the attack on Tempo Moderate testnet within a Docker environment. Download the PoC and run:

unzip mppx_typescript_PoC.zip
cd mppx_typescript
docker build -t mppx-padding .
docker run --rm mppx-padding

There are more details in mppx_typescript/README.md

Impact

A malicious client can force the server to pay ~5x the normal transaction fee. This dramatically increases operational costs and completely destroys the profit margin on low-cost items.

Please provide a way to share the PoC in .zip format to you. Thank you!

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`mppx`	all versions	0.8.2`npm install mppx@0.8.2`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mppx, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mppx to 0.8.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-727h-3vm5-qwq6 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Details When the server acts as the fee_payer, `mppx` 0.6.27 validates calldata using viem's `decodeFunctionData`, 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. **Vulnerable code

O3 Security · Impact-Aware SCA

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