guzzlehttp/psr7: CRLF Injection in HTTP Start-Line Serialization

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Summary

CVECVE-2026-55766
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-23 16:17:03 UTC
Updated2026-06-23 17:57:05 UTC
Descriptionguzzlehttp/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.

Risk And Classification

Primary CVSS: v3.1 4.8 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Problem Types: CWE-93 | CWE-113 | CWE-93 CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection') | CWE-113 CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary4.8MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
3.1CNADECLARED4.8MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Guzzle Psr7 affected < 2.12.1 Not specified

References

ReferenceSourceLinkTags
github.com/guzzle/psr7/security/advisories/GHSA-vm85-hxw5-5432 [email protected] github.com
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