Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
The guzzlehttp/guzzle Packagist package, versions before 7.12.1, accepts cookies whose Domain attribute contains only dots (such as "Domain=.") and treats them as matching any request host. An attacker who controls an origin that an application requests through a shared cookie jar can set such a cookie and have Guzzle send it to unrelated hosts, which may enable cookie injection or session fixation depending on the downstream services. Upgrade to version 7.12.1 or later, which rejects dot-only Domain attributes; if upgrading is not possible, use separate cookie jars per trust boundary.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 5.8 | Medium | 3.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N | CNA (GitHub_M) |
- CISA KEV Not listed.
- EPSS 0.0021, the 11th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 14:01 UTC First seen by agentprime
- 31 Oct 2026, 14:01 UTC Confirmed by OSV
Sources
- GitHub Advisory Database: GHSA-cwxw-98qj-8qjx
- OSV: GHSA-cwxw-98qj-8qjx
- github.com/guzzle/guzzle/security/advisories/GHSA-cwxw-98qj-8qjx
- nvd.nist.gov/vuln/detail/CVE-2026-55767
- github.com/guzzle/guzzle/pull/3653
- github.com/guzzle/guzzle/commit/7f537cded1912349abf5081258d6db19106d774d
- github.com/FriendsOfPHP/security-advisories/blob/master/guzzlehttp/guzzle/CVE-2026-55767.yaml
- github.com/guzzle/guzzle
- github.com/guzzle/guzzle/releases/tag/7.12.1