CVE-2026-55767 Guzzle: Dot-Only Cookie Domains Match All Hosts in guzzlehttp/guzzle
Attackers can inject cookies into unrelated hosts via a shared cookie jar due to improper domain validation, potentially enabling session fixation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55767?
CVE-2026-55767 is a medium-severity vulnerability in guzzle, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-55767?
2 open source packages ship an affected version, including guzzlehttp/guzzle. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
guzzlehttp/guzzle Packagist | All versions | 7.12.1 |
guzzlehttp/guzzle Packagist | All versions | 7.12.1 |
Products include Guzzlephp Guzzle.
How do I fix CVE-2026-55767?
Upgrade guzzlehttp/guzzle to 7.12.1 or later.
Is CVE-2026-55767 being exploited?
There is no known exploitation of CVE-2026-55767 in the wild and no public exploit code.
Other vulnerabilities in guzzle
Sources
Also known as DEBIAN-CVE-2026-55767, GHSA-cwxw-98qj-8qjx, MINI-6x4g-qq74-jhhf, MINI-86p7-rr25-ghg2, MINI-8jv2-vm6m-m7wf, MINI-8v7r-q5m4-fgx9 and 6 more.