Vulnerability-Lookup

GHSA-F4GW-2P7V-4548

Vulnerability from github – Published: 2026-07-20 22:20 – Updated: 2026-07-20 22:20

Summary

Axios: NO_PROXY bypass for 0.0.0.0 local addresses in axios

Details

Summary

Axios versions containing lib/helpers/shouldBypassProxy.js do not treat 0.0.0.0 as a local address when evaluating NO_PROXY rules. In Node.js applications that use HTTP_PROXY or HTTPS_PROXY together with NO_PROXY=localhost,127.0.0.1,::1 or similar, a request to http://0.0.0.0:<port>/ can be routed through the configured proxy instead of bypassing it.

The issue is exploitable when an attacker can influence the axios request URL or a followed redirect target, and when the proxy can reach or relay 0.0.0.0 to local services. This is a Node.js runtime proxy-routing issue, not a browser, install-time, or development-tooling issue.

Impact

Applications are affected when all of the following are true:

The application runs axios in Node.js with the HTTP adapter.
The process uses environment proxy variables such as HTTP_PROXY or HTTPS_PROXY.
The process uses NO_PROXY entries such as localhost, 127.0.0.1, or ::1 to keep local traffic out of the proxy path.
Attacker-controlled input can influence the request URL or redirect target.
The configured proxy does not reject 0.0.0.0 and can reach the local destination.

For plain HTTP targets, the proxy can receive the full request URL, headers, and body, and may be able to observe the local service response. HTTPS targets are less exposed because axios uses CONNECT tunneling in current versions.

Affected Functionality

Affected functionality is limited to environment-derived proxy selection in the Node HTTP adapter:

lib/adapters/http.js calls getProxyForUrl(location) and then shouldBypassProxy(location) before applying the proxy.
lib/helpers/shouldBypassProxy.js normalizes and compares NO_PROXY entries.
Explicit caller-provided config.proxy remains trusted caller configuration.
Browser, React Native, XHR, and fetch adapter behavior are not affected.

Technical Details

lib/helpers/shouldBypassProxy.js defines local loopback equivalence through isLoopback(). The current implementation recognizes localhost, IPv4 127.0.0.0/8, IPv6 ::1, and IPv4-mapped loopback forms, but it does not include 0.0.0.0.

At lib/helpers/shouldBypassProxy.js:176, axios treats two hosts as matching when both are considered loopback:

return hostname === entryHost || (isLoopback(hostname) && isLoopback(entryHost));

Because isLoopback('0.0.0.0') returns false, NO_PROXY=localhost,127.0.0.1,::1 does not match http://0.0.0.0:<port>/. lib/adapters/http.js:185-193 then applies the environment proxy.

Proof of Concept of Attack

import http from 'http';
import axios from './index.js';

const listen = (handler, host = '127.0.0.1') =>
  new Promise((resolve) => {
    const server = http.createServer(handler);
    server.listen(0, host, () => resolve(server));
  });

const close = (server) => new Promise((resolve) => server.close(resolve));

const origin = await listen((req, res) => res.end('origin'), '0.0.0.0');

let proxyRequests = 0;
const proxy = await listen((req, res) => {
  proxyRequests += 1;
  res.end('proxied');
});

process.env.http_proxy = `http://127.0.0.1:${proxy.address().port}`;
process.env.HTTP_PROXY = process.env.http_proxy;
process.env.no_proxy = 'localhost,127.0.0.1,::1';
process.env.NO_PROXY = process.env.no_proxy;

try {
  const direct = await axios.get(`http://127.0.0.1:${origin.address().port}/`);
  const zero = await axios.get(`http://0.0.0.0:${origin.address().port}/`);

  console.log({ direct: direct.data, zero: zero.data, proxyRequests });
} finally {
  await close(origin);
  await close(proxy);
}

Expected safe behavior: both 127.0.0.1 and 0.0.0.0 bypass the proxy when the NO_PROXY policy is intended to cover local destinations.

Observed behavior: 127.0.0.1 bypasses the proxy, while 0.0.0.0 is sent through the proxy.

Workarounds

Add 0.0.0.0 explicitly to NO_PROXY where local addresses must bypass proxies.
Reject or normalize 0.0.0.0 in application URL validation before calling axios.
Set proxy: false on axios requests that must never use environment proxies.
Configure the proxy itself to reject 0.0.0.0, loopback, link-local, and internal address ranges.

Original Report ### Summary `axios` versions 1.15.0–1.16.1 contain an incomplete loopback-address check in `lib/helpers/shouldBypassProxy.js`. The `isLoopback()` function correctly identifies `127.0.0.0/8` and `::1` as loopback addresses but does not recognise `0.0.0.0` — the IPv4 unspecified address, which routes to the local machine on Linux and macOS. An attacker who controls a URL passed to axios can use `http://0.0.0.0/` to bypass proxy-based SSRF filtering that the application relies upon. ### Details ## Affected versions `>= 1.15.0, <= 1.16.1` The vulnerability was introduced in v1.15.0 when the `shouldBypassProxy` helper was added as a security improvement (PR #10661). --- ## Root cause **File:** `lib/helpers/shouldBypassProxy.js` ```javascript // Line 1 — static allowlist (incomplete) const LOOPBACK_HOSTNAMES = new Set(['localhost']); // ← 0.0.0.0 missing const isIPv4Loopback = (host) => { const parts = host.split('.'); if (parts.length !== 4) return false; if (parts[0] !== '127') return false; // ← 0.0.0.0: parts[0] = '0' → false return parts.every((p) => /^\d+$/.test(p) && Number(p) >= 0 && Number(p) <= 255); }; const isLoopback = (host) => { if (!host) return false; if (LOOPBACK_HOSTNAMES.has(host)) return true; // ← '0.0.0.0' not in set if (isIPv4Loopback(host)) return true; // ← returns false for 0.0.0.0 return isIPv6Loopback(host); }; isLoopback('0.0.0.0') returns false. Node's WHATWG URL parser does not normalise 0.0.0.0 to 127.0.0.1. Other bypass forms are safe: new URL('http://0177.0.0.1/').hostname → '127.0.0.1' (octal), new URL('http://2130706433/').hostname → '127.0.0.1' (decimal), new URL('http://0x7f000001/').hostname → '127.0.0.1' (hex). Only 0.0.0.0 escapes normalisation. ### PoC 'use strict'; // Verbatim copy of relevant logic from axios v1.16.1 shouldBypassProxy.js const LOOPBACK_HOSTNAMES = new Set(['localhost']); const isIPv4Loopback = (host) => { const parts = host.split('.'); if (parts.length !== 4) return false; if (parts[0] !== '127') return false; return parts.every((p) => /^\d+$/.test(p) && Number(p) >= 0 && Number(p) <= 255); }; const isLoopback = (host) => { if (!host) return false; if (LOOPBACK_HOSTNAMES.has(host)) return true; return isIPv4Loopback(host); }; // 1. Show URL parser does NOT normalise 0.0.0.0 console.log(new URL('http://0.0.0.0/').hostname); // → '0.0.0.0' ← NOT normalised console.log(new URL('http://0177.0.0.1/').hostname); // → '127.0.0.1' ← normalised (safe) console.log(new URL('http://2130706433/').hostname); // → '127.0.0.1' ← normalised (safe) // 2. Show isLoopback fails for 0.0.0.0 console.log(isLoopback('0.0.0.0')); // → false ← BUG: should be true console.log(isLoopback('127.0.0.1')); // → true ← correct Verified output on Node.js v22 / axios v1.16.1: 0.0.0.0 ← NOT normalised by URL parser 127.0.0.1 ← octal normalised correctly 127.0.0.1 ← decimal normalised correctly false ← 0.0.0.0 not detected as loopback ⚠ true ← 127.0.0.1 correctly detected ### Impact Applications that: Accept user-supplied URLs and pass them to axios Use a proxy with NO_PROXY=localhost (or similar) for SSRF filtering …can be bypassed by supplying http://0.0.0.0/. Axios routes the request through the proxy (shouldBypassProxy returns false). If the proxy itself does not filter 0.0.0.0, the connection reaches the local machine — exposing internal services such as cloud IMDS endpoints, internal admin panels, or microservice APIs. Fix Minimal (one line): - const LOOPBACK_HOSTNAMES = new Set(['localhost']); + const LOOPBACK_HOSTNAMES = new Set(['localhost', '0.0.0.0']); Comprehensive: const isIPv4Unspecified = (host) => host === '0.0.0.0'; const isLoopback = (host) => { if (!host) return false; if (LOOPBACK_HOSTNAMES.has(host)) return true; if (isIPv4Loopback(host)) return true; if (isIPv4Unspecified(host)) return true; // add this line return isIPv6Loopback(host); };

Severity

6.9 (Medium)


                  
                    CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:H/SI:N/SA:N

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "axios"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.15.0"
            },
            {
              "fixed": "1.18.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "axios"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.31.0"
            },
            {
              "fixed": "0.33.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-183",
      "CWE-918"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-20T22:20:18Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nAxios versions containing `lib/helpers/shouldBypassProxy.js` do not treat `0.0.0.0` as a local address when evaluating `NO_PROXY` rules. In Node.js applications that use `HTTP_PROXY` or `HTTPS_PROXY` together with `NO_PROXY=localhost,127.0.0.1,::1` or similar, a request to `http://0.0.0.0:\u003cport\u003e/` can be routed through the configured proxy instead of bypassing it.\n\nThe issue is exploitable when an attacker can influence the axios request URL or a followed redirect target, and when the proxy can reach or relay `0.0.0.0` to local services. This is a Node.js runtime proxy-routing issue, not a browser, install-time, or development-tooling issue.\n\n## Impact\n\nApplications are affected when all of the following are true:\n\n- The application runs axios in Node.js with the HTTP adapter.\n- The process uses environment proxy variables such as `HTTP_PROXY` or `HTTPS_PROXY`.\n- The process uses `NO_PROXY` entries such as `localhost`, `127.0.0.1`, or `::1` to keep local traffic out of the proxy path.\n- Attacker-controlled input can influence the request URL or redirect target.\n- The configured proxy does not reject `0.0.0.0` and can reach the local destination.\n\nFor plain HTTP targets, the proxy can receive the full request URL, headers, and body, and may be able to observe the local service response. HTTPS targets are less exposed because axios uses CONNECT tunneling in current versions.\n\n## Affected Functionality\n\nAffected functionality is limited to environment-derived proxy selection in the Node HTTP adapter:\n\n- `lib/adapters/http.js` calls `getProxyForUrl(location)` and then `shouldBypassProxy(location)` before applying the proxy.\n- `lib/helpers/shouldBypassProxy.js` normalizes and compares `NO_PROXY` entries.\n- Explicit caller-provided `config.proxy` remains trusted caller configuration.\n- Browser, React Native, XHR, and fetch adapter behavior are not affected.\n\n## Technical Details\n\n`lib/helpers/shouldBypassProxy.js` defines local loopback equivalence through `isLoopback()`. The current implementation recognizes `localhost`, IPv4 `127.0.0.0/8`, IPv6 `::1`, and IPv4-mapped loopback forms, but it does not include `0.0.0.0`.\n\nAt `lib/helpers/shouldBypassProxy.js:176`, axios treats two hosts as matching when both are considered loopback:\n\n```js\nreturn hostname === entryHost || (isLoopback(hostname) \u0026\u0026 isLoopback(entryHost));\n```\n\nBecause `isLoopback(\u00270.0.0.0\u0027)` returns `false`, `NO_PROXY=localhost,127.0.0.1,::1` does not match `http://0.0.0.0:\u003cport\u003e/`. `lib/adapters/http.js:185-193` then applies the environment proxy.\n\n## Proof of Concept of Attack\n\n```js\nimport http from \u0027http\u0027;\nimport axios from \u0027./index.js\u0027;\n\nconst listen = (handler, host = \u0027127.0.0.1\u0027) =\u003e\n  new Promise((resolve) =\u003e {\n    const server = http.createServer(handler);\n    server.listen(0, host, () =\u003e resolve(server));\n  });\n\nconst close = (server) =\u003e new Promise((resolve) =\u003e server.close(resolve));\n\nconst origin = await listen((req, res) =\u003e res.end(\u0027origin\u0027), \u00270.0.0.0\u0027);\n\nlet proxyRequests = 0;\nconst proxy = await listen((req, res) =\u003e {\n  proxyRequests += 1;\n  res.end(\u0027proxied\u0027);\n});\n\nprocess.env.http_proxy = `http://127.0.0.1:${proxy.address().port}`;\nprocess.env.HTTP_PROXY = process.env.http_proxy;\nprocess.env.no_proxy = \u0027localhost,127.0.0.1,::1\u0027;\nprocess.env.NO_PROXY = process.env.no_proxy;\n\ntry {\n  const direct = await axios.get(`http://127.0.0.1:${origin.address().port}/`);\n  const zero = await axios.get(`http://0.0.0.0:${origin.address().port}/`);\n\n  console.log({ direct: direct.data, zero: zero.data, proxyRequests });\n} finally {\n  await close(origin);\n  await close(proxy);\n}\n```\n\nExpected safe behavior: both `127.0.0.1` and `0.0.0.0` bypass the proxy when the `NO_PROXY` policy is intended to cover local destinations.\n\nObserved behavior: `127.0.0.1` bypasses the proxy, while `0.0.0.0` is sent through the proxy.\n\n## Workarounds\n\n- Add `0.0.0.0` explicitly to `NO_PROXY` where local addresses must bypass proxies.\n- Reject or normalize `0.0.0.0` in application URL validation before calling axios.\n- Set `proxy: false` on axios requests that must never use environment proxies.\n- Configure the proxy itself to reject `0.0.0.0`, loopback, link-local, and internal address ranges.\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal Report\u003c/summary\u003e\n\n### Summary\n`axios` versions 1.15.0\u20131.16.1 contain an incomplete loopback-address check in `lib/helpers/shouldBypassProxy.js`. The `isLoopback()` function correctly identifies `127.0.0.0/8` and `::1` as loopback addresses but does not recognise `0.0.0.0` \u2014 the IPv4 unspecified address, which routes to the local machine on Linux and macOS.\n\nAn attacker who controls a URL passed to axios can use `http://0.0.0.0/\u003cpath\u003e` to bypass proxy-based SSRF filtering that the application relies upon.\n\n### Details\n## Affected versions\n\n`\u003e= 1.15.0, \u003c= 1.16.1`\n\nThe vulnerability was introduced in v1.15.0 when the `shouldBypassProxy` helper was added as a security improvement (PR #10661).\n\n---\n\n## Root cause\n\n**File:** `lib/helpers/shouldBypassProxy.js`\n\n```javascript\n// Line 1 \u2014 static allowlist (incomplete)\nconst LOOPBACK_HOSTNAMES = new Set([\u0027localhost\u0027]);   // \u2190 0.0.0.0 missing\n\nconst isIPv4Loopback = (host) =\u003e {\n  const parts = host.split(\u0027.\u0027);\n  if (parts.length !== 4) return false;\n  if (parts[0] !== \u0027127\u0027) return false;   // \u2190 0.0.0.0: parts[0] = \u00270\u0027 \u2192 false\n  return parts.every((p) =\u003e /^\\d+$/.test(p) \u0026\u0026 Number(p) \u003e= 0 \u0026\u0026 Number(p) \u003c= 255);\n};\n\nconst isLoopback = (host) =\u003e {\n  if (!host) return false;\n  if (LOOPBACK_HOSTNAMES.has(host)) return true;   // \u2190 \u00270.0.0.0\u0027 not in set\n  if (isIPv4Loopback(host)) return true;           // \u2190 returns false for 0.0.0.0\n  return isIPv6Loopback(host);\n};\n\nisLoopback(\u00270.0.0.0\u0027) returns false.\n\nNode\u0027s WHATWG URL parser does not normalise 0.0.0.0 to 127.0.0.1. Other bypass forms are safe: new URL(\u0027http://0177.0.0.1/\u0027).hostname \u2192 \u0027127.0.0.1\u0027 (octal), new URL(\u0027http://2130706433/\u0027).hostname \u2192 \u0027127.0.0.1\u0027 (decimal), new URL(\u0027http://0x7f000001/\u0027).hostname \u2192 \u0027127.0.0.1\u0027 (hex). Only 0.0.0.0 escapes normalisation.\n\n\n### PoC\n\u0027use strict\u0027;\n\n// Verbatim copy of relevant logic from axios v1.16.1 shouldBypassProxy.js\n\nconst LOOPBACK_HOSTNAMES = new Set([\u0027localhost\u0027]);\n\nconst isIPv4Loopback = (host) =\u003e {\n  const parts = host.split(\u0027.\u0027);\n  if (parts.length !== 4) return false;\n  if (parts[0] !== \u0027127\u0027) return false;\n  return parts.every((p) =\u003e /^\\d+$/.test(p) \u0026\u0026 Number(p) \u003e= 0 \u0026\u0026 Number(p) \u003c= 255);\n};\n\nconst isLoopback = (host) =\u003e {\n  if (!host) return false;\n  if (LOOPBACK_HOSTNAMES.has(host)) return true;\n  return isIPv4Loopback(host);\n};\n\n// 1. Show URL parser does NOT normalise 0.0.0.0\nconsole.log(new URL(\u0027http://0.0.0.0/\u0027).hostname);    // \u2192 \u00270.0.0.0\u0027   \u2190 NOT normalised\nconsole.log(new URL(\u0027http://0177.0.0.1/\u0027).hostname); // \u2192 \u0027127.0.0.1\u0027 \u2190 normalised (safe)\nconsole.log(new URL(\u0027http://2130706433/\u0027).hostname);  // \u2192 \u0027127.0.0.1\u0027 \u2190 normalised (safe)\n\n// 2. Show isLoopback fails for 0.0.0.0\nconsole.log(isLoopback(\u00270.0.0.0\u0027));   // \u2192 false  \u2190 BUG: should be true\nconsole.log(isLoopback(\u0027127.0.0.1\u0027)); // \u2192 true   \u2190 correct\n\nVerified output on Node.js v22 / axios v1.16.1:\n0.0.0.0     \u2190 NOT normalised by URL parser\n127.0.0.1   \u2190 octal normalised correctly\n127.0.0.1   \u2190 decimal normalised correctly\nfalse       \u2190 0.0.0.0 not detected as loopback  \u26a0\ntrue        \u2190 127.0.0.1 correctly detected\n\n### Impact\nApplications that:\n\nAccept user-supplied URLs and pass them to axios\nUse a proxy with NO_PROXY=localhost (or similar) for SSRF filtering\n\u2026can be bypassed by supplying http://0.0.0.0/\u003cpath\u003e. Axios routes the request through the proxy (shouldBypassProxy returns false). If the proxy itself does not filter 0.0.0.0, the connection reaches the local machine \u2014 exposing internal services such as cloud IMDS endpoints, internal admin panels, or microservice APIs.\n\nFix\nMinimal (one line):\n\n- const LOOPBACK_HOSTNAMES = new Set([\u0027localhost\u0027]);\n+ const LOOPBACK_HOSTNAMES = new Set([\u0027localhost\u0027, \u00270.0.0.0\u0027]);\n\nComprehensive:\n\nconst isIPv4Unspecified = (host) =\u003e host === \u00270.0.0.0\u0027;\n\nconst isLoopback = (host) =\u003e {\n  if (!host) return false;\n  if (LOOPBACK_HOSTNAMES.has(host)) return true;\n  if (isIPv4Loopback(host)) return true;\n  if (isIPv4Unspecified(host)) return true;   // add this line\n  return isIPv6Loopback(host);\n};\n\u003c/details\u003e",
  "id": "GHSA-f4gw-2p7v-4548",
  "modified": "2026-07-20T22:20:18Z",
  "published": "2026-07-20T22:20:18Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/security/advisories/GHSA-f4gw-2p7v-4548"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/pull/11000"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/pull/11001"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/commit/1417285c69344bbcc6420a021f67dee0c6fedb2d"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/commit/32fc489632377d214db55bfa4e2c48486a7d7ce2"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/axios/axios"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/releases/tag/v0.33.0"
    },
    {
      "type": "WEB",
      "url": "https://github.com/axios/axios/releases/tag/v1.18.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:H/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Axios: NO_PROXY bypass for 0.0.0.0 local addresses in axios"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

Action not permitted

GHSA-F4GW-2P7V-4548

Summary

Impact

Affected Functionality

Technical Details

Proof of Concept of Attack

Workarounds

Tags

Sightings

Nomenclature