CVE-2025-27820: Apache HttpClient Auth Bypass Vulnerability

CVE-2025-27820 Overview

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.

Critical Impact

This vulnerability compromises cookie management and host name verification, potentially leading to security breaches involving incorrect domain validation.

Affected Products

• Apache HttpClient
• NetApp ONTAP Tools

Discovery Timeline

• Not Available - Vulnerability discovered by Apache HttpClient team
• Not Available - Responsible disclosure to Apache
• Not Available - CVE CVE-2025-27820 assigned
• Not Available - Apache releases security patch
• 2025-04-24 - CVE CVE-2025-27820 published to NVD
• 2025-07-16 - Last updated in NVD database

Technical Details for CVE-2025-27820

Vulnerability Analysis

The vulnerability arises from a bug in the Public Suffix List (PSL) validation logic within Apache HttpClient 5.4.x. This defect effectively disables domain-related checks in critical functions like cookie management and hostname verification, potentially allowing malicious domains to bypass these checks and engage in unauthorized activities.

Root Cause

The root cause is an incorrect implementation in PSL processing, which improperly handles domain validation.

Attack Vector

This vulnerability can be exploited over the Network, making any system using the affected versions susceptible to remote attacks that exploit the validation logic flaw.

// Example exploitation code (sanitized)
HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
    .uri(new URI("http://malicious.example.com"))
    .build();

client.sendAsync(request, BodyHandlers.ofString())
    .thenApply(HttpResponse::body)
    .thenAccept(System.out::println);

Detection Methods for CVE-2025-27820

Indicators of Compromise

• Unexpected access to unverified domains
• Logs showing domain validation errors
• Unauthorized cookie acceptance from untrusted domains

Detection Strategies

Deploy network monitoring tools to identify unauthorized access attempts to unverified domains. Analyze HttpClient logs for validation anomalies and unexpected domain-related errors.

Monitoring Recommendations

Use IDS/IPS systems to alert on unusual domain patterns and implement alerts for suspicious cookie transactions.

How to Mitigate CVE-2025-27820

Immediate Actions Required

• Upgrade to Apache HttpClient version 5.4.3 or later.
• Review domain validation settings in applications using HttpClient.
• Conduct a security audit on existing domain validation logic.

Patch Information

Refer to the Apache HttpClient release notes for patch details and upgrade instructions.

Workarounds

Enforce strict domain validation checks through application-side logic where possible. Disable or heavily scrutinize cookie acceptance logic.

# Configuration example
export APACHE_HTTPCLIENT_VERSION=5.4.3