CVE-2026-55766: guzzlehttp/psr7: CRLF Injection in HTTP Start-Line Serialization
guzzle · psr7
Affected: guzzle psr7 · Exploitation: unlikely (under 1%)
Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.
Higher than 13% of scored CVEs
DescriptionCVE.org
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.
Affected products1
From the CVE record. A product or version that is not listed is unknown, not unaffected.
- guzzle · psr7< 2.12.1
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CoverageNo articles yet
No CyberSIXT article names CVE-2026-55766 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.