CVE-2026-67353: Guzzle: Unbounded response cookies risk denial of service

Impact

In affected versions, Guzzle's built-in CookieJar accepts any number of Set-Cookie header fields from one response, with no limit on the size of each field. When a later request matches the stored cookies, Guzzle places every match into one generated Cookie header without limiting the number of cookies or the total header length.

A malicious or compromised server can therefore return many large cookies, causing Guzzle to store attacker-controlled data in memory and copy it into later request headers. This can increase memory use and processing time. It can also make later requests fail when the generated header exceeds a limit in a handler, HTTP implementation, proxy, or destination server. A server on one sibling host, such as attacker.example.com, can also set parent-domain cookies that are later selected for another sibling, such as service.example.com. The denial can therefore affect a different service that uses the same jar.

An application is affected when it enables the built-in cookie support, receives an attacker-controlled response, and retains or reuses the jar. The issue affects both built-in handlers because Guzzle manages these cookies itself instead of using libcurl's native cookie engine. cURL addressed a similar denial-of-service issue in CVE-2022-32205 by limiting the cookies it accepts and sends, but those native limits do not protect Guzzle's separate jar. Applications that do not use cookies, use separate jars for untrusted origins, or use a third-party CookieJarInterface with suitable limits are not affected by this behavior. The demonstrated direct impact is limited to availability. The patch does not impose a lifetime limit on a jar built up over an unlimited number of responses or populated directly by application code.

Patches

The issue is patched in 7.15.1 and later. Starting in that release, the built-in CookieJar ignores a Set-Cookie field value longer than 8,190 bytes and applies at most 50 successful cookie insertions or replacements from one response. When generating a request, it emits at most 150 matching name=value pairs and limits the complete Cookie: header line to 8,190 bytes, including the field name and following space.

These limits follow the same practical shape as cURL's response to CVE-2022-32205. Both bound cookies accepted from one response, cookies added to one request, and generated header size. Guzzle's 8,190-byte incoming field limit is more generous than cURL's current 5,000-byte cookie-line limit. Neither approach adds a global jar quota or an eviction policy. The 8,190-byte incoming boundary is inclusive. Invalid, unrelated, identical, oversized, and deletion fields do not consume the 50-cookie limit. For outgoing requests, Guzzle preserves its existing matching and iteration order. It stops after 150 pairs or before the first matching cookie that would exceed the line limit. The output limits also apply to directly imported cookie state, but that state is not limited when it is added to the jar. Explicit caller-supplied Cookie headers and third-party jar implementations remain the caller's responsibility. Versions before 7.15.1 are affected.

Workarounds

If you cannot upgrade immediately, do not enable a shared built-in cookie jar for requests to untrusted origins. Use separate jars per host or trust boundary, disable cookie handling for untrusted requests, and discard or clear a jar after receiving an untrusted response before it is reused. Applications that must accept cookies from untrusted peers can provide a custom CookieJarInterface implementation that enforces suitable limits.

Guzzle does not use libcurl's cookie engine for cookies stored in a CookieJar. The cURL handler sends the Cookie header that Guzzle's cookie middleware has already built, so libcurl's cookie limits do not apply. Upgrading libcurl therefore does not fix this issue.

References

https://curl.se/docs/CVE-2022-32205.html https://www.rfc-editor.org/rfc/rfc10025.html#section-5.7 https://www.rfc-editor.org/rfc/rfc10025.html#section-5.8.3 https://www.rfc-editor.org/rfc/rfc10025.html#section-6.1