CRLF Injection Affecting guzzlehttp/psr7 package, versions <2.12.1
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PHP-GUZZLEHTTPPSR7-17393718
- published22 Jun 2026
- disclosed19 Jun 2026
- creditIlia Alshanetsky
Introduced: 19 Jun 2026
NewCVE-2026-55766 (opens in a new tab)How to fix?
Upgrade guzzlehttp/psr7 to version 2.12.1 or higher.
Overview
Affected versions of this package are vulnerable to CRLF Injection in the start-line serialization of the Message class (toString, parseRequest, and parseResponse). An attacker can inject header lines and split or smuggle HTTP messages by placing CR or LF characters into the request method, protocol version, or response reason phrase, which are not rejected before the message is serialized as raw HTTP/1.x. Exploitation requires attacker-controlled data to reach one of these start-line fields and the serialized message to be processed by a downstream HTTP component, so standard client usage is unaffected while custom transports and manual serialization are.