CVE-2026-55767: Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, CookieJar incorrectly accepts cookies with a dot-only Domain attribute and whitespace-padded...

Description

Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, CookieJar incorrectly accepts cookies with a dot-only Domain attribute and whitespace-padded variants. SetCookie::matchesDomain() removes leading dots from the cookie domain, normalizing dot-only values to the empty string; SetCookie::validate() only rejected a strictly empty domain, so these cookies could be stored and the empty normalized domain was treated as matching any request host. An attacker-controlled origin that an application requests with a shared cookie jar can therefore set a cookie that Guzzle later sends to unrelated hosts using the same jar. This may allow cookie injection or session fixation against downstream services, depending on how those services interpret the injected cookie. This vulnerability is fixed in 7.12.1.

Metrics

CVSS 3.1

5.8/10

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

EPSS Probability

0.11%

1.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Guzzlephp	Guzzle	< 7.12.1

References

https://github.com/guzzle/guzzle/security/advisories/GHSA-cwxw-98qj-8qjxThird Party Advisory

Timeline

Published: Jun 23, 2026
Last Modified: Jun 26, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-55767?

Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, CookieJar incorrectly accepts cookies with a dot-only Domain attribute and whitespace-padded variants. SetCookie::matchesDomain() removes leading dots from the cookie domain, normalizing dot-only values to the empty string; SetCookie::validate() only rejected a strictly empty domain, so these cookies could be stored and the empty normalized domain was treated as matching any request host. An attacker-controlled origin that an application requests with a shared cookie jar can therefore set a cookie that Guzzle later sends to unrelated hosts using the same jar. This may allow cookie injection or session fixation against downstream services, depending on how those services interpret the injected cookie. This vulnerability is fixed in 7.12.1.

How severe is CVE-2026-55767?

CVE-2026-55767 has a CVSS score of 5.8/10 (MEDIUM severity). The EPSS model estimates a 0.11% probability of exploitation in the next 30 days.

How do I fix CVE-2026-55767?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.