CVE-2026-63628 — mppx
Fix: wevm/mppx@24ddccaCVE-2026-63628 is a Improper Input Validation vulnerability in mppx. A fix is available for mppx — see the affected versions and patch details below.
mppx: Gas Draining with access list
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-63628.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
Real-World Exposure
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.
mppxnpmDescription
Details
When the server acts as the fee_payer, mppx 0.6.27 copies the client-supplied EIP-2930 access list verbatim into the cosigned fee-payer transaction. The TypeScript SDK's fee-payer cosigning path accepts any access_list the client includes in the 0x78 FeePayerEnvelope without inspecting its length or contents.
Access list gas is charged intrinsically — before any opcode executes — regardless of whether the listed addresses are ever touched.
An attacker submits a valid transferWithMemo alongside fabricated address-only access list entries. The server validates calldata and gas parameters but never inspects access_list length. It cosigns and broadcasts a transaction that costs the fee-payer wallet N × 2,400 extra gas per request with no corresponding work performed on-chain.
At the default of 180 entries and 100 Gwei max_fee_per_gas, this inflates the fee-payer cost from the normal ~51,287 gas to ~483,287 gas — a 9.4× multiplier — while staying within the FeePayerPolicy cap of 500K gas, the Node.js 16 KB header limit, and the Moderato RPC's eth_call simulation budget (verified empirically at 180 entries).
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-typescript-access-list .
docker run --rm mppx-typescript-access-list
There are more details in mppx_typescript/README.md
Impact
A malicious client can force the server to pay ~9.4x the normal transaction fee. This dramatically increases operational costs and completely destroys the profit margin on low-cost items.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | mppx | all versions | 0.8.2npm install mppx@0.8.2 |
Detection & mitigation playbook
Open-source dependencyDetect
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 CVE-2026-63628 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
Is CVE-2026-63628 in your dependencies?
Find it across npm, including transitive dependencies.