CVE-2026-101899

Axios is a promise-based HTTP client for the browser and Node.js. From 1.15.0 until 1.20.0, Axios shouldBypassProxy treats the NO_PROXY CIDR form as a textual hostname suffix instead of evaluating the network range. A request targets an address covered by a CIDR entry in NO_PROXY while a proxy is configured. The CIDR bypass rule is not matched, so the request is sent through the configured proxy. For plaintext HTTP, the proxy can observe and modify URLs, headers, and bodies; for HTTPS, it can observe connection metadata and CONNECT requests. This issue is fixed in version 1.20.0.

Axios is a promise-based HTTP client for the browser and Node.js. From 1.15.0 until 1.20.0, Axios shouldBypassProxy treats the NO_PROXY CIDR form as a textual hostname suffix instead of evaluating the network range. A request targets an address covered by a CIDR entry in NO_PROXY while a proxy is configured. The CIDR bypass rule is not matched, so the request is sent through the configured proxy. For plaintext HTTP, the proxy can observe and modify URLs, headers, and bodies; for HTTPS, it can observe connection metadata and CONNECT requests. This issue is fixed in version 1.20.0.

Summary

Axios supports proxy environment variables and evaluates NO_PROXY exclusions in the Node.js adapter. CIDR-form NO_PROXY entries such as 127.0.0.0/8, 10.0.0.0/8, or 169.254.169.254/32 are not interpreted as IP ranges. As a result, a request to an IP address inside a configured CIDR exclusion can still be sent through the configured proxy.

This affects deployments that rely on CIDR notation to keep loopback, private, Kubernetes, CI, or cloud metadata traffic away from proxy infrastructure.

Impact

If the configured proxy is outside the intended trust boundary, requests that operators expected to bypass the proxy may be exposed to it. For plaintext HTTP targets, the proxy can see and modify URLs, headers, and bodies. For HTTPS targets, the proxy still observes connection metadata and may receive CONNECT requests that policy expected to avoid.

This is a proxy exclusion bypass, not arbitrary proxy injection by itself.

Affected Functionality

Affected:

• Node.js adapter proxy environment handling.
• HTTP_PROXY, HTTPS_PROXY, NO_PROXY, or lowercase equivalents.
• CIDR entries in NO_PROXY.

Not affected:

• Exact host or exact IP NO_PROXY entries where axios matching succeeds.
• Requests configured with proxy: false.
• Browser adapters.

Technical Details

lib/helpers/shouldBypassProxy.js parses each NO_PROXY entry into a host and optional port, normalizes hostnames, and then compares exact hostnames, suffix entries, wildcard-prefix entries, and loopback equivalents. It does not parse CIDR notation.

Local verification on axios 1.18.1:

process.env.NO_PROXY = '127.0.0.0/8';
shouldBypassProxy('http://127.0.0.1:1234/'); // false

The expected result for CIDR-aware bypass policy is true.

Proof of Concept of Attack

Constrained local demonstration:

1. Set HTTP_PROXY=http://127.0.0.1:<proxy-port>.
2. Set NO_PROXY=127.0.0.0/8.
3. Request http://127.0.0.1:<internal-port>/metadata.
4. Observe that axios sends the request through the proxy instead of directly to the internal listener.

Workarounds

Use exact host or IP entries in NO_PROXY for sensitive destinations until CIDR matching is fixed, for example 127.0.0.1,localhost,169.254.169.254. For individual requests that must not use a proxy, set proxy: false.

<details> <summary><h3>Original report</h3></summary>

Summary

Axios 1.17.0 honors HTTP_PROXY / HTTPS_PROXY and supports NO_PROXY host exclusions, but CIDR-form NO_PROXY entries such as 127.0.0.0/8 are not treated as network ranges. As a result, requests to IPs covered by a configured CIDR exclusion may still be sent through the configured proxy.

In the attached PoC, a request to 127.0.0.1 is sent through HTTP_PROXY despite NO_PROXY=127.0.0.0/8.

This can cause proxy exclusion bypass in environments where operators use CIDR notation to exclude loopback, private, internal, Kubernetes, CI, or cloud metadata address ranges from proxying.

Details

Axios supports proxy environment variables, including HTTP_PROXY / HTTPS_PROXY and NO_PROXY-style exclusions. Axios’s threat model treats environment proxy handling as security-relevant and lists NO_PROXY as a mitigation for proxy environment variable hijack, including hardening for CIDR ranges, IPv6 literals, and wildcard patterns. See: https://github.com/axios/axios/blob/a8e4f13aeecc45a3b8fab3ecfd9ddb5d70fb772b/THREATMODEL.md#t-r9-proxy-environment-variable-hijack

The issue is that CIDR-form NO_PROXY entries are not interpreted as network ranges. For example:

NO_PROXY=127.0.0.0/8
HTTP_PROXY=http://127.0.0.1:<proxy-port>
Target URL=http://127.0.0.1:<internal-port>/metadata

Since 127.0.0.1 is inside 127.0.0.0/8, an operator may reasonably expect Axios to bypass the proxy for this request. Instead, Axios sends the request through HTTP_PROXY.

This appears to affect the proxy bypass decision path used for NO_PROXY / no_proxy handling. The relevant…

Axios is a promise-based HTTP client for the browser and Node.js. From 1.15.0 until 1.20.0, Axios shouldBypassProxy treats the NO_PROXY CIDR form as a textual hostname suffix instead of evaluating the network range. A request targets an address covered by a CIDR entry in NO_PROXY while a proxy is configured. The CIDR bypass rule is not matched, so the request is sent through the configured proxy. For plaintext HTTP, the proxy can observe and modify URLs, headers, and bodies; for HTTPS, it can observe connection metadata and CONNECT requests. This issue is fixed in version 1.20.0.

Axios is a promise-based HTTP client for the browser and Node.js. From 1.15.0 until 1.20.0, Axios shouldBypassProxy treats the NO_PROXY CIDR form as a textual hostname suffix instead of evaluating the network range. A request targets an address covered by a CIDR entry in NO_PROXY while a proxy is configured. The CIDR bypass rule is not matched, so the request is sent through the configured proxy. For plaintext HTTP, the proxy can observe and modify URLs, headers, and bodies; for HTTPS, it can observe connection metadata and CONNECT requests. This issue is fixed in version 1.20.0.

Axios is a promise-based HTTP client for the browser and Node.js. From 1.15.0 until 1.20.0, Axios shouldBypassProxy treats the NO_PROXY CIDR form as a textual hostname suffix instead of evaluating the network range. A request targets an address covered by a CIDR entry in NO_PROXY while a proxy is configured. The CIDR bypass rule is not matched, so the request is sent through the configured proxy. For plaintext HTTP, the proxy can observe and modify URLs, headers, and bodies; for HTTPS, it can observe connection metadata and CONNECT requests. This issue is fixed in version 1.20.0.