🛡️ CVE-2026-55766 on Ubuntu — php-guzzlehttp-psr7

⚪ Unknown ✅ No Known Exploit OSV
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

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.

Distribution advisory

This page covers CVE-2026-55766 as tracked by Ubuntu, for the package php-guzzlehttp-psr7. No fixed version has been recorded for this distribution yet.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality low, integrity low, availability none.

Affected software

UBUNTU-CVE-2026-55766 is recorded against 1 package.

  • php-guzzlehttp-psr7

Timeline and source

Published on 23 June 2026 and last revised on 25 June 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

ubuntu.com (Report)
www.cve.org (Report)
github.com (Report)

Details

Severity Unknown
CVSS Score N/A
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
CWE N/A
Public Exploit ✅ No
Source OSV
Published 2026-06-23
Updated 2026-08-11
Modified 2026-06-25
Fix URL N/A

Affected Packages

Software From version Fixed in
php-guzzlehttp-psr7 — —

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