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CVE-2026-42039 high CVSS 7.5

Vulnerability in axios (CVE-2026-42039)

Summary

Vulnerability in axios (CVE-2026-42039). Risk of unauthorized operations or information disclosure. Exploitable via POST /forward. Mitigation: upgrade to 0.31.1 or later.

Original description

The description as published by the source.

Summary

toFormData recursively walks nested objects with no depth limit, so a deeply nested value passed as request data crashes the Node.js process with a RangeError.

Details

lib/helpers/toFormData.js:210 defines an inner build(value, path) that recurses into every object/array child (line 225: build(el, path ? path.concat(key) : [key])). The only safeguard is a stack array used to detect circular references; there is no maximum depth and no try/catch around the recursion. Because build calls itself once per nesting level, a payload nested roughly 2000+ levels deep exhausts V8's call stack.

toFormData is the serializer behind FormData request bodies and AxiosURLSearchParams (used by buildURL when params is an object with URLSearchParams unavailable, see lib/helpers/buildURL.js:53 and lib/helpers/AxiosURLSearchParams.js:36). Any server-side code that forwards a client-supplied object into axios({ data, params }) therefore reaches the recursive walker with attacker-controlled depth.

The RangeError is thrown synchronously from inside forEach, escapes toFormData, and propagates out of the axios request call. In typical Express/Fastify request handlers this terminates the running request; in synchronous startup paths or worker threads it can crash the whole process.

PoC

import toFormData from 'axios/lib/helpers/toFormData.js';
import FormData from 'form-data';

function nest(depth) {
  let o = { leaf: 1 };
  for (let i = 0; i <…

Source: GitHub Security Advisories (Global) 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-2026-42039 has been found in axios.
Attackers can target a specific entry point like POST /forward over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade axios to 0.31.1 or later.
If unsure, ask your IT team or search "axios CVE-2026-42039" on the vendor's site.

CVE-2026-42039 (axios) — CWE-674 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: POST /forward / stack / build / toFormData
Patched: 0.31.1 — 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.

❓ What is the problem

A vulnerability (CWE-674) exists in axios. Attackers reach the vulnerable code path via POST /forward without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of axios. Attack surface: POST /forward / stack / build / toFormData.

🔥 Severity

Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 0.31.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual POST /forward requests with malformed payloads or SQL meta-characters. Run grep -r 'axios' . 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

  1. 1
    Identify exposure identify 
    grep -r 'axios' . | 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 axios を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Hunt for indicators of compromise detect 
    grep 'POST /forward' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'

    アクセスログで POST /forward への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。

  3. 3
    Apply patch patch 
    Upgrade axios to 0.31.1

    ステージング環境で 0.31.1 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と、Step 2 で見つけた異常検知の続報チェックを含めること。

  4. 4
    Post-deployment verification verify 
    Replay attack against POST /forward on staging to confirm patch closes the vector

    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 Step 2 と同じログクエリでアラート再発が無いか継続監視。

Affected packages

npm axios
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"0.31.1"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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