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CVE-2025-27820: Apache HttpClient PSL Validation Logic Bug

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Overview

A critical vulnerability has been identified in Apache HttpClient 5.4.x. This vulnerability, classified under the CVE ID CVE-2025-27820, arises from a bug in the PSL (Public Suffix List) validation logic which disables domain checks, primarily affecting cookie management and hostname verification. This weakness could potentially lead to a system compromise or data leakage, making it a significant risk to organizations using the affected versions of Apache HttpClient.

Vulnerability Summary

CVE ID: CVE-2025-27820
Severity: High (CVSS: 7.5)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise or data leakage

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Product | Affected Versions

Apache HttpClient | 5.4.0 to 5.4.2

How the Exploit Works

The exploitation of this vulnerability can occur when a malicious actor sends a specially crafted request to the server using the affected versions of Apache HttpClient. Due to the bug in the PSL validation logic, the software does not perform adequate domain checks. This flaw can be leveraged to manipulate cookie management and hostname verification, potentially leading to unauthorized access or extraction of sensitive data.

Conceptual Example Code

Here is a conceptual example of how this vulnerability might be exploited:

POST /vulnerable/endpoint HTTP/1.1
Host: target.example.com
Cookie: sessionid=malicious_cookie
{
"malicious_payload": "..."
}

In this example, the attacker exploits the PSL validation logic bug to inject a malicious cookie into the HTTP request. Successful exploitation could compromise the system and potentially lead to data leakage.

Mitigation Guidance

Users are advised to mitigate this vulnerability by applying the vendor patch as soon as possible. The Apache HttpClient team has released version 5.4.3, which resolves the identified bug. As a temporary mitigation measure, organizations can also use a Web Application Firewall (WAF) or an Intrusion Detection System (IDS) to detect and prevent exploitation attempts.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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