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GHSA-vm85-hxw5-5432
No affected components available
Impact
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 is not the normal request-sending path used by guzzlehttp/guzzle; applications using guzzlehttp/psr7 only through Guzzle's standard HTTP client APIs are not expected to be affected.
Applications are most likely to be affected when they manually serialize PSR-7 messages, forward raw HTTP messages, or use custom transports, proxying, crawling, webhook delivery, testing, or similar code. Depending on how downstream HTTP/1.1 components parse the serialized message, this may lead to header injection, response splitting, request smuggling, or cache poisoning.
Patches
The issue is patched in 2.12.1 and later. Starting in that release, guzzlehttp/psr7 rejects CR/LF characters in HTTP method, protocol version, and response reason phrase values before storing them in first-party message objects.
Workarounds
If you cannot upgrade immediately, reject CR/LF in untrusted method, protocol version, and reason phrase values before constructing or modifying PSR-7 messages.
Applications that parse, forward, replay, or serialize raw HTTP messages cannot work around the parser entry points by validating only after parsing. They should validate the raw start line before calling Message::parseRequest() or Message::parseResponse(), avoid reparsing untrusted raw messages, or upgrade. If an application runs with attacker-controlled synthetic $_SERVER values, validate REQUEST_METHOD and SERVER_PROTOCOL before calling ServerRequest::fromGlobals().
The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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