CVE-2026-55766

MEDIUM EPSS 5.3%
Published Jun 23, 20261w ago · Modified Jun 23, 20261w ago
4.8 CVSS 3.1
Medium
Find Similar
Published Jun 23, 2026 1w ago
Last Modified Jun 23, 2026 1w ago

Description

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.

CVSS Details

Base Score
4.8
Exploitability
2.2
Impact
2.5
Vector string
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
Attack Vector Network
Attack Complexity High
Privileges Required None
User Interaction None
Scope Unchanged
Confidentiality Low
Integrity Low
Availability None

Threat Intelligence

EPSS Exploit Probability
5.3% percentile
Exploit & Patch Status
No Known Exploit
No Patch Available

Weaknesses 2

CWE-113
CWE-93

References 1

  • github.com https://github.com/guzzle/psr7/security/advisories/GHSA-vm85-hxw5-5432

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.