CVE-2026-59883 guzzle CVE debrief

Who should care

Users of Guzzle PHP HTTP client versions prior to 7.12.3 should update to the latest version to prevent potential cross-host cookie disclosure, cookie injection, or session fixation attacks. Affected operators, platforms, and security teams should review the official advisory and CVE record to validate affected systems and plan vendor-supported updates or mitigations.

Technical summary

Guzzle PHP HTTP client versions prior to 7.12.3 contain a vulnerability in CookieJar that allows cross-host cookie disclosure, cookie injection, or session fixation due to improper domain matching. The issue is fixed in version 7.12.3. This vulnerability requires specific conditions to be exploited but can have significant impacts if successful. Defenders should review compensating controls for exposed systems while remediation is scheduled and verified.

Defensive priority

Medium priority, as the vulnerability requires specific conditions to be exploited, but can have significant impacts if successful.

Recommended defensive actions

• Update Guzzle PHP HTTP client to version 7.12.3 or later
• Review and update affected systems and applications
• Monitor for suspicious activity related to cookie disclosure or injection
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The CVE record and NVD detail provide information on the vulnerability, its impact, and the fixed version. Additional details can be found in the Guzzle GitHub repository. Evidence limits suggest that further verification is needed to confirm affected scope and severity. Defenders should review the official advisory and CVE record to validate affected systems and plan vendor-supported updates or mitigations.

Official resources