CVE-2026-49214

guzzlehttp/psr7 has CRLF Injection via URI Host Component

if (preg_match('/[\x00-\x20\x7F]/', $untrustedUrl)) {
    throw new \InvalidArgumentException('Insecure URL detected');
}

guzzlehttp/psr7 did not reject ASCII control characters, whitespace, or DEL in first-party URI host components. The issue requires a PSR-7 request to be serialized into a raw HTTP/1.x message, for example with GuzzleHttp\Psr7\Message::toString() or an equivalent custom serializer. Creating a Uri, Request, or other PSR-7 object alone is not sufficient. The malformed host must be copied into the serialized Host header without further validation.

A vulnerable flow is:

1. An application accepts a user-controlled URL.
2. The URL is used to construct a PSR-7 Uri or Request.
3. The host component contains CRLF or another header-unsafe character.
4. The request is serialized into a raw HTTP/1.x message without an explicit Host header.
5. The host is copied into the serialized Host header.
6. The serialized request is written to the network or otherwise processed by software that does not independently reject the malformed host.

In that flow, an attacker can cause the serialized request to contain additional attacker-controlled header lines. For example, a host containing "\r\nX-Injected: yes" can cause the generated Host header to span multiple HTTP header lines.

This is not the normal request-sending path used by guzzlehttp/guzzle. Applications using guzzlehttp/psr7 only through Guzzle's standard HTTP client APIs are not expected to be affected. Applications are most likely to be affected when they manually serialize PSR-7 requests, forward raw HTTP messages, or use custom transports, proxying, crawling, webhook delivery, or similar request-dispatch code that serializes requests without independently validating URI hosts and header data. In deployments involving HTTP/1.1 connection reuse, proxies, gateways, or load balancers, this malformed serialized request may also contribute to request smuggling or cache poisoning, depending on how downstream components parse the request.

The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.

CVE-2026-49214 has a CVSS score of 5.3 (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 (2.10.2); upgrading removes the vulnerable code path.

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The issue is patched in 2.10.2 and later. 1.x is end-of-life and will not receive a patch.

1. What is CVE-2026-49214? CVE-2026-49214 is a medium-severity improper input validation vulnerability in guzzlehttp/psr7 (composer), affecting versions < 2.10.2. It is fixed in 2.10.2. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
2. How severe is CVE-2026-49214? CVE-2026-49214 has a CVSS score of 5.3 (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 guzzlehttp/psr7 are affected by CVE-2026-49214? guzzlehttp/psr7 (composer) versions < 2.10.2 is affected.
4. Is there a fix for CVE-2026-49214? Yes. CVE-2026-49214 is fixed in 2.10.2. Upgrade to this version or later.
5. Is CVE-2026-49214 exploitable, and should I be worried? Whether CVE-2026-49214 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-2026-49214 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-2026-49214? Upgrade guzzlehttp/psr7 to 2.10.2 or later.

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