# 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.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Jun 2026
- **Updated:** 5 Aug 2026
- **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, MINI-fwqc-gp7j-jv84, MINI-m88g-3pw7-f3vp, MINI-p52p-mx6f-fh67, MINI-pr9v-65j4-xvv9, MINI-rv7r-j887-9mh8, UBUNTU-CVE-2026-55767

## 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.

Weakness: CWE-346 (Origin Validation Error), CWE-1286 (Improper Validation of Syntactic Correctness of Input)

## Which versions are affected by CVE-2026-55767?

2 open source packages ship an affected version, including guzzlehttp/guzzle. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `guzzlehttp/guzzle` | Packagist | All versions | 7.12.1 |
| `guzzlehttp/guzzle` | Packagist | All versions | 7.12.1 |

Products: 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

- [CVE-2026-55568](https://insights.sbomify.com/CVE-2026-55568/): Guzzle: Silent HTTPS-Proxy Downgrade to Cleartext (medium 5.9)
- [CVE-2026-59883](https://insights.sbomify.com/CVE-2026-59883/): Guzzle: Cookie Disclosure and Injection via IP-Address Domains (medium 4.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55767 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-55767 in the wild and no public exploit code.

Affected packages and fixed versions:
- guzzlehttp/guzzle (Packagist): affected all versions; fixed in 7.12.1
- guzzlehttp/guzzle (Packagist): affected all versions; fixed in 7.12.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55767/ (Markdown: https://insights.sbomify.com/CVE-2026-55767/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55767
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55767
- OSV: https://osv.dev/vulnerability/CVE-2026-55767

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55767/
Summaries are generated and may contain mistakes; the official description above is the record.