Axios: Incomplete Fix for CVE-2025-62718 — NO_PROXY Protection Bypassed via RFC 1122 Loopback Subnet (127.0.0.0/8) in

**1. Executive Summary** This report documents an **incomplete security patch** for the previously disclosed vulnerability **GHSA-3p68-rc4w-qgx5 (CVE-2025-62718)**, which affects the `NO_PROXY` hostname resolution logic in the Axios HTTP library. **Background — The Original Vulnerability** The original vulnerability (GHSA-3p68-rc4w-qgx5) disclosed that Axios did not normalize hostnames before comparing them against `NO_PROXY` rules. Specifically, a request to `http://localhost./` (with a trailing dot) or `http://[::1]/` (with IPv6 bracket notation) would **bypass NO_PROXY matching entirely** and be forwarded to the configured HTTP proxy — even when `NO_PROXY=localhost,127.0.0.1,::1` was explicitly set by the developer to protect loopback services. The Axios maintainers addressed this in **version 1.15.0** by introducing a `normalizeNoProxyHost()` function in `lib/helpers/shouldBypassProxy.js`, which strips trailing dots from hostnames and removes brackets from IPv6 literals before performing the NO_PROXY comparison. **The Incomplete Patch — This Finding** While the patch correctly addresses the specific cases reported (trailing dot normalization and IPv6 bracket removal), **the fix is architecturally incomplete**. The patch introduced a hardcoded set of recognized loopback addresses: ``` // lib/helpers/shouldBypassProxy.js — Line 1 const LOOPBACK_ADDRESSES = new Set(['localhost', '127.0.0.1', '::1']); ``` However, **RFC 1122 §3.2.1.3** explicitly defines the **entire 127.0.0.0/8 subnet** as the IPv4 loopback address block not just the single address `127.0.0.1`. On all major operating systems (Linux, macOS, Windows with WSL), any IP address in the range `127.0.0.2` through `127.255.255.254` is a valid, functional loopback address that routes to the local machine. As a result, an attacker who can influence the target URL of an Axios request can substitute 127.0.0.1 with any other address in the `127.0.0.0/8` range (e.g., `127.0.0.2`, `127.0.0.100`, `127.1.2.3`) to **completely bypass** the `NO_PROXY` protection even in the fully patched Axios 1.15.0 release. **Verification** This bypass has been **independently verified** on: * **Axios version:** 1.15.0 (latest patched release) * **Node.js version:** v22.16.0 * **OS:** Kali Linux (rolling) The Proof-of-Concept demonstrates that while `localhost`, `localhost`., and `[::1]` are correctly blocked by the patched version, requests to `127.0.0.2`, `127.0.0.100`, and `127.1.2.3` are **transparently forwarded to the attacker-controlled proxy server**, confirming that the patch does not cover the full RFC-defined loopback address space. **2. Deep-Dive: Technical Root Cause Analysis** **2.1 Vulnerable File & Location** | Field | Detail | | ------------- | ------------- | | File | lib/helpers/shouldBypassProxy.js| | Primary Flaw| isLoopback() — Line 1–3 | | Supporting Function | shouldBypassProxy() — Line 59–110 | | Axios Version | 1.15.0 (Latest Patched Release) | **2.2 How Axios Routes HTTP Requests The Call Chain** When Axios dispatches any HTTP request, `lib/adapters/http.js` calls `setProxy()`, which invokes `shouldBypassProxy()` to decide whether to honour a configured proxy: ``` // lib/adapters/http.js — Lines 191–199 function setProxy(options, configProxy, location) { let proxy = configProxy; if (!proxy && proxy !== false) { const proxyUrl = getProxyForUrl(location); // Step 1: Read proxy env var if (proxyUrl) { if (!shouldBypassProxy(location)) { // Step 2: Check NO_PROXY proxy = new URL(proxyUrl); // Step 3: Assign proxy } } } } ``` `shouldBypassProxy()` is the **single gatekeeper** for NO_PROXY enforcement. A bypass here means all proxy protection fails silently. **2.3 The Original Vulnerability (GHSA-3p68-rc4w-qgx5)** Before Axios 1.15.0, hostnames were compared against `NO_PROXY` using a **raw literal string match** with no normalization: ``` Request URL → http://localhost./secret NO_PROXY → "localhost,127.0.0.1,::1" Comparison: "localhost." === "localhost" → FALSE → Proxy used ← BYPASS "[::1]" === "::1" → FALSE → Proxy used ← BYPASS ``` Both `localhost.` (FQDN trailing dot, RFC 1034 §3.1) and `[::1]` (bracketed IPv6 literal, RFC 3986 §3.2.2) are **canonical representations of loopback addresses**, but Axios treated them as unknown hosts. **2.4 What the Patch Fixed (Axios 1.15.0)** The patch introduced three changes inside `lib/helpers/shouldBypassProxy.js`: <img width="602" height="123" alt="01_axios_version_verification" src="https://github.com/user-attachments/assets/844446f2-01fb-4933-9316-fb849c40c8f5" /> **Fix A `normalizeNoProxyHost()` (Lines 47–57)** Strips alternate representations before comparison: ``` const normalizeNoProxyHost = (hostname) => { if (!hostname) return hostname; // Remove IPv6 brackets: "[::1]" → "::1" if (hostname.charAt(0) === '[' && hostname.charAt(hostname.length - 1) === ']') { hostname = hostname.slice(

• github.com/axios/axios/security/advisories/GHSA-pmwg-cvhr-8vh7 (opens in a new tab)
• nvd.nist.gov/vuln/detail/CVE-2026-42043 (opens in a new tab)
• github.com/axios/axios (opens in a new tab)

• CVE-2025-62718: Axios has a NO_PROXY Hostname Normalization Bypass that Leads to SSRFMediumVulnerability2026-04-09
• Red Hat Security Advisory: Red Hat Quay 3.15.5HighVulnerability2026-06-09
• Red Hat Security Advisory: Red Hat Quay 3.10.22HighVulnerability2026-06-03
• Red Hat Security Advisory: Red Hat Quay 3.17.2HighVulnerability2026-06-02
• Red Hat Security Advisory: RHACS 4.10.3 security and bug fix updateHighVulnerability2026-05-26