CVE-2026-55767
CVE-2026-55767 is a medium-severity vulnerability in Guzzlephp Guzzle with a CVSS 3.x base score of 5.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-346.
Key facts
- Severity: Medium (CVSS 3.x base score 5.8)
- EPSS exploit prediction: 0% (2nd percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-38457
- Weakness: CWE-346
- Affected product: Guzzlephp Guzzle
- Published:
- Last modified:
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.
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 3.x base score of 5.8, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
- Is CVE-2026-55767 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (2nd percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-55767?
- CVE-2026-55767 affects Guzzlephp Guzzle. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-55767?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-55767 have an EU (EUVD) identifier?
- Yes. CVE-2026-55767 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-38457.
- When was CVE-2026-55767 published?
- CVE-2026-55767 was published on 2026-06-23 and last updated on 2026-06-26.
References
Affected products (1)
- cpe:2.3:a:guzzlephp:guzzle:*:*:*:*:*:*:*:*
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