CVE-2026-55766 - Medium Severity Vulnerability
Vulnerable Library - guzzlehttp/psr7-2.9.x-dev
PSR-7 message implementation that also provides common utility methods
Library home page: https://api.github.com/repos/guzzle/psr7/zipball/7d0ed42f28e42d61352a7a79de682e5e67fec884
Dependency Hierarchy:
- guzzlehttp/guzzle-7.10.0 (Root Library)
- ❌ guzzlehttp/psr7-2.9.x-dev (Vulnerable Library)
Found in HEAD commit: 81f84f058af0cbca57ee22476557ded21c6813aa
Found in base branch: master
Vulnerability Details
guzzlehttp/psr7 is a PSR-7 HTTP message library implementation in PHP. Prior to 2.12.1, guzzlehttp/psr7 did not reject CR/LF characters in certain first-party HTTP start-line fields: the request method, protocol version, and response reason phrase. If an application placed attacker-controlled data into one of those fields and later serialized the PSR-7 message as raw HTTP/1.x, for example with Message::toString() or an equivalent serializer, the serialized message could contain attacker-controlled header lines. The issue can also be reached through Message::parseRequest() or Message::parseResponse() when malformed raw messages are parsed into first-party PSR-7 objects and then serialized again. Creating or modifying a Request, Response, or other PSR-7 object alone is not sufficient. The issue requires the malformed message to be serialized and written to the network, forwarded, replayed, or otherwise processed by software that does not independently reject the malformed start line. This vulnerability is fixed in 2.12.1.
Publish Date: 2026-06-23
URL: CVE-2026-55766
CVSS 3 Score Details (4.8)
Base Score Metrics:
- Exploitability Metrics:
- Attack Vector: Network
- Attack Complexity: High
- Privileges Required: None
- User Interaction: None
- Scope: Unchanged
- Impact Metrics:
- Confidentiality Impact: Low
- Integrity Impact: Low
- Availability Impact: None
For more information on CVSS3 Scores, click here.
Suggested Fix
Type: Upgrade version
Origin: GHSA-cwxw-98qj-8qjx
Release Date: 2026-06-19
Fix Resolution: guzzlehttp/psr7 - 2.12.1
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CVE-2026-55766 - Medium Severity Vulnerability
PSR-7 message implementation that also provides common utility methods
Library home page: https://api.github.com/repos/guzzle/psr7/zipball/7d0ed42f28e42d61352a7a79de682e5e67fec884
Dependency Hierarchy:
Found in HEAD commit: 81f84f058af0cbca57ee22476557ded21c6813aa
Found in base branch: master
guzzlehttp/psr7 is a PSR-7 HTTP message library implementation in PHP. Prior to 2.12.1, guzzlehttp/psr7 did not reject CR/LF characters in certain first-party HTTP start-line fields: the request method, protocol version, and response reason phrase. If an application placed attacker-controlled data into one of those fields and later serialized the PSR-7 message as raw HTTP/1.x, for example with Message::toString() or an equivalent serializer, the serialized message could contain attacker-controlled header lines. The issue can also be reached through Message::parseRequest() or Message::parseResponse() when malformed raw messages are parsed into first-party PSR-7 objects and then serialized again. Creating or modifying a Request, Response, or other PSR-7 object alone is not sufficient. The issue requires the malformed message to be serialized and written to the network, forwarded, replayed, or otherwise processed by software that does not independently reject the malformed start line. This vulnerability is fixed in 2.12.1.
Publish Date: 2026-06-23
URL: CVE-2026-55766
Base Score Metrics:
- Exploitability Metrics:
- Attack Vector: Network
- Attack Complexity: High
- Privileges Required: None
- User Interaction: None
- Scope: Unchanged
- Impact Metrics:
- Confidentiality Impact: Low
- Integrity Impact: Low
- Availability Impact: None
For more information on CVSS3 Scores, click here.Type: Upgrade version
Origin: GHSA-cwxw-98qj-8qjx
Release Date: 2026-06-19
Fix Resolution: guzzlehttp/psr7 - 2.12.1
Step up your Open Source Security Game with Mend here