CVE-2026-49214: guzzlehttp/psr7 has CRLF Injection via URI Host Component
Impact
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.
Patches
The issue is patched in 2.10.2 and later. 1.x is end-of-life and will not receive a patch.
Workarounds
If you cannot upgrade immediately, validate and reject all untrusted URI strings before constructing PSR-7 Uri or Request instances. Reject input containing ASCII control characters, whitespace, or DEL, including CRLF, tab, space, NUL, or DEL characters:
php if (pregmatch('/[\x00-\x20\x7F]/', $untrustedUrl)) { throw new \InvalidArgumentException('Insecure URL detected'); }
Applications that manually serialize or forward requests should also ensure the final HTTP client, transport, or serializer rejects invalid URI and header data before writing requests to the network.
References
https://www.rfc-editor.org/rfc/rfc9112.html#section-3.2 https://www.rfc-editor.org/rfc/rfc9112.html#section-5 https://www.rfc-editor.org/rfc/rfc9112.html#section-11.2 https://www.rfc-editor.org/rfc/rfc9110.html#section-7.2
Other sources
guzzlehttp/psr7 is a PSR-7 HTTP message library implementation in PHP. Versions prior to 2.10.2 did not reject ASCII control characters, whitespace, or DEL in first-party URI host components. A vulnerable flow is: First, an application accepts a user-controlled URL. Second, the URL is used to construct a PSR-7 Uri or Request. Third, the host component contains CRLF or another header-unsafe character. Fourth, the host is copied into the PSR-7 Host header when no explicit Host header is provided. Finally, the request is serialized or sent by an HTTP client 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. Applications are affected when they use user-controlled URLs for outbound HTTP requests, URL forwarding, proxying, crawling, webhook delivery, or similar request-dispatch flows. In deployments involving HTTP/1.1 connection reuse, proxies, gateways, or load balancers, this malformed request may also contribute to request smuggling or cache poisoning, depending on how downstream components parse the request. The issue is patched in 2.10.2 and later. 1.x is end-of-life and will not receive a patch. As a workaround, validate and reject all untrusted URI strings before constructing PSR-7 Uri or Request instances. Reject input containing ASCII control characters, whitespace, or DEL, including CRLF, tab, space, NUL, or DEL characters. Applications that forward requests should also ensure the final HTTP client or serializer rejects invalid URI and header data before writing requests to the network.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/guzzlehttp/psr7to a version that resolves this vulnerability.Fixed in 2.10.2 - Configuration
Validate and reject all untrusted URI strings before constructing PSR-7 Uri or Request instances. Reject input containing ASCII control characters, whitespace, or DEL (including CRLF, tab, space, NUL). Example check: if (preg_match('/[\x00-\x20\x7F]/', $untrustedUrl)) { throw new \InvalidArgumentException('Insecure URL detected'); }
Application input validation reject_untrusted_uri_strings_containing_ASCII_control_whitespace_DEL = true - Compensating control
Ensure the final HTTP client, transport, or serializer rejects invalid URI and header data before writing requests to the network. Do not rely solely on application-level construction of PSR-7 objects when serializing requests.
- Compensating control
Prefer using guzzlehttp/guzzle's standard HTTP client APIs rather than manually serializing or forwarding PSR-7 requests. Applications that only use Guzzle's standard client APIs are not expected to be affected.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-49214?
The severity of CVE-2026-49214 is medium with a score of 5.3.
How do I fix CVE-2026-49214?
To fix CVE-2026-49214, upgrade guzzlehttp/psr7 to version 2.10.2 or later.
What type of vulnerability is CVE-2026-49214?
CVE-2026-49214 is a CRLF Injection vulnerability related to input validation.
Which versions of guzzlehttp/psr7 are affected by CVE-2026-49214?
Versions of guzzlehttp/psr7 prior to 2.10.2 are affected by CVE-2026-49214.
What can an attacker exploit in CVE-2026-49214?
An attacker can exploit CVE-2026-49214 by injecting ASCII control characters into the URI host components of a user-controlled URL.