CVE-2025-27820 in HttpComponents
Summary
by MITRE • 04/24/2025
A bug in PSL validation logic in Apache HttpClient 5.4.x disables domain checks, affecting cookie management and host name verification. Discovered by the Apache HttpClient team. Fixed in the 5.4.3 release
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Analysis
by VulDB Data Team • 07/18/2025
The vulnerability identified as CVE-2025-27820 represents a critical flaw in the Public Suffix List (PSL) validation logic within Apache HttpClient 5.4.x versions. This issue specifically impacts the cookie management system and hostname verification mechanisms that are fundamental to secure HTTP communications. The bug was discovered internally by the Apache HttpClient development team during routine security assessments and subsequent code reviews. The vulnerability manifests when the library fails to properly validate domain names against the public suffix list, which is essential for preventing cross-site scripting attacks and ensuring proper cookie security boundaries. The PSL validation is designed to identify the registrable domain portion of a hostname by excluding public suffixes such as .com, .org, .co.uk, and similar top-level domains that are shared across multiple organizations. When this validation logic is compromised, it allows malicious actors to potentially bypass security restrictions that should prevent cookies from being set or accessed across different domains.
The technical implementation of this vulnerability stems from an error in how the HttpClient library processes hostname validation during cookie management operations. The PSL validation logic is supposed to ensure that cookies are only set for domains that match the expected security boundaries, but the bug causes the system to accept invalid domain patterns that should be rejected. This flaw specifically affects the HostnameVerifier interface and CookieOriginValidator components within the HTTP client library. When a server responds with a Set-Cookie header containing a domain attribute, the HttpClient library should verify that the domain is valid and properly formatted according to the PSL rules. The bug essentially disables this verification step, allowing cookies to be set for domains that should be considered invalid or potentially malicious. This creates a scenario where attackers could potentially manipulate cookie behavior by crafting domain names that bypass the validation checks, leading to potential session hijacking or cross-site request forgery vulnerabilities.
The operational impact of CVE-2025-27820 extends beyond simple cookie management issues and represents a significant threat to the overall security posture of applications that rely on Apache HttpClient 5.4.x for HTTP communications. Systems using affected versions may experience unauthorized cookie access, where malicious domains could potentially set cookies that should be restricted to specific registrable domains. This vulnerability aligns with CWE-295, which addresses improper certificate validation and hostname verification issues in network communication libraries. The flaw creates opportunities for attackers to exploit the trust relationships established by HTTP cookie mechanisms, potentially allowing them to access sensitive session information or manipulate user authentication states. Applications that process user authentication tokens, maintain session cookies, or handle sensitive data through HTTP communications are particularly vulnerable. The vulnerability also has implications for the MITRE ATT&CK framework under the T1190 technique, which covers exploiting vulnerabilities in network protocols and communication libraries. The impact is further compounded because this vulnerability affects the foundational security mechanisms of HTTP client libraries, meaning that any application relying on Apache HttpClient for secure communications could be exposed to these risks without proper mitigation.
Organizations using affected Apache HttpClient versions should immediately upgrade to release 5.4.3 or later to address this vulnerability. The fix implemented in version 5.4.3 corrects the PSL validation logic by ensuring proper hostname verification and domain checking during cookie management operations. Security teams should conduct comprehensive audits of their applications to identify any systems still running vulnerable versions of the library and ensure that all HTTP client components are updated accordingly. The remediation process should include not only updating the Apache HttpClient library but also reviewing existing cookie handling logic to verify that no applications are relying on the flawed validation behavior. Additionally, organizations should implement monitoring for any unusual cookie behavior or unauthorized access patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date security libraries and conducting regular security assessments of third-party components. System administrators should also consider implementing network-level monitoring to detect potential exploitation attempts that might leverage this vulnerability for more sophisticated attacks. The fix addresses the root cause by restoring proper validation of domain names against the public suffix list, ensuring that cookie security boundaries are maintained according to established security standards and best practices.