CVE-2026-59883 in Guzzle
Summary
by MITRE • 07/08/2026
Guzzle is an extensible PHP HTTP client. Prior to 7.12.3, CookieJar did not restrict cookies scoped to IP-address or bare-numeric Domain values to the exact host that set them, because SetCookie::matchesDomain() applied ordinary suffix matching to domains such as 192.168.0.1, [::1], or 1, allowing cross-host cookie disclosure, cookie injection, or session fixation. This issue is fixed in version 7.12.3.
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Analysis
by VulDB Data Team • 07/08/2026
The vulnerability in Guzzle's CookieJar component represents a critical security flaw that undermines the fundamental principles of web application security and session management. This issue affects versions prior to 7.12.3 and stems from improper cookie domain validation logic within the SetCookie::matchesDomain() method. The flaw specifically impacts cookies that are scoped to IP address values or bare numeric domains, creating a dangerous bypass in the standard cookie security model that should prevent cross-host cookie access.
The technical implementation of this vulnerability occurs when Guzzle processes cookies with domain attributes containing IP addresses such as 192.168.0.1, IPv6 addresses like [::1], or simple numeric values like 1. The SetCookie::matchesDomain() method applies standard suffix matching logic to these values instead of enforcing strict host-based matching, which allows cookies set by one host to be sent to and potentially accepted by different hosts sharing the same numeric domain pattern. This behavior directly violates the cookie security model that requires strict host validation to prevent unauthorized cross-site cookie access.
The operational impact of this vulnerability is severe and multifaceted, encompassing several critical attack vectors including cross-host cookie disclosure, cookie injection, and session fixation attacks. An attacker could exploit this weakness by manipulating cookies to be accepted across different hosts within the same numeric domain range, potentially allowing them to hijack sessions or inject malicious cookies into applications that rely on Guzzle's HTTP client implementation. This vulnerability particularly affects environments where applications use IP-based hostnames or where numeric domains are common in internal network configurations.
This security issue aligns with CWE-284, which addresses improper access control mechanisms, and represents a specific manifestation of weak cookie validation practices that can lead to privilege escalation attacks. The vulnerability also maps to ATT&CK technique T1548.002, specifically "Abuse Elevation Control Mechanism: Bypass User Account Control," through the session hijacking capabilities it enables when combined with other exploitation techniques. Organizations using Guzzle versions prior to 7.12.3 face significant risk of credential theft and unauthorized access to sensitive application resources.
The fix implemented in version 7.12.3 addresses this issue by modifying the SetCookie::matchesDomain() method to properly handle IP address and numeric domain values through exact host matching rather than suffix matching. This change ensures that cookies scoped to IP addresses or numeric domains are restricted to the exact host that set them, preventing unauthorized cross-host cookie access. Security teams should prioritize updating to version 7.12.3 or later immediately, as this vulnerability can be exploited without user interaction and may have been actively targeted in environments with internal IP address-based configurations.
Organizations should conduct comprehensive security assessments of their applications using Guzzle to identify any potential exploitation vectors related to cookie handling and IP-based hostnames. The remediation process involves not only updating the Guzzle library but also reviewing application code that might rely on specific cookie behaviors, particularly in internal network environments where numeric domains are common. System administrators should monitor for any suspicious cookie-related activity that might indicate exploitation attempts, as this vulnerability can be used to establish persistent access to applications without requiring additional authentication credentials.