Vulnerability in mppx (CVE-2026-63627)
Summary
Vulnerability in mppx (CVE-2026-63627). Risk of unauthorized operations or information disclosure. Exploitable via mppx. Mitigation: upgrade to 0.8.2 or later.
Original description
The description as published by the source.
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…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-63627 has been found in mppx.
Attackers can target a specific entry point like mppx over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade mppx to 0.8.2 or later.
If unsure, ask your IT team or search "mppx CVE-2026-63627" on the vendor's site.
CVE-2026-63627 (mppx) — CWE-20
Attack surface: mppx / decodeFunctionData / FeePayerPolicy / gas_limit
Patched: 0.8.2 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-20) exists in mppx. Attackers reach the vulnerable code path via mppx.
Check the vendor advisory for the affected versions of mppx. Attack surface: mppx / decodeFunctionData / FeePayerPolicy / gas_limit.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 0.8.2.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'mppx' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'mppx' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
mppxを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade mppx to 0.8.2ステージング環境で 0.8.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
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3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
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- web github.com