CVE-2025-22227: Reactor Netty Credential Leak Vulnerability

CVE-2025-22227 Overview

CVE-2025-22227 is an Information Leakage vulnerability affecting the Reactor Netty HTTP client. In specific scenarios involving chained redirects, the HTTP client may inadvertently leak credentials to unintended destinations. This vulnerability requires that the HTTP client has been explicitly configured to follow redirects, making it a configuration-dependent security issue.

Critical Impact

Applications using Reactor Netty HTTP client with redirect following enabled may unintentionally expose authentication credentials to third-party servers through chained redirect sequences, potentially compromising sensitive access tokens and user credentials.

Affected Products

• Reactor Netty HTTP client (specific vulnerable versions not disclosed)
• Spring-based applications utilizing Reactor Netty for HTTP requests
• Applications with explicit redirect-following configuration enabled

Discovery Timeline

• 2025-07-16 - CVE CVE-2025-22227 published to NVD
• 2025-07-16 - Last updated in NVD database

Technical Details for CVE-2025-22227

Vulnerability Analysis

This vulnerability is classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The issue manifests when an application using Reactor Netty HTTP client follows a chain of HTTP redirects. During this redirect chain processing, authentication credentials that were intended for the original destination may be forwarded to subsequent redirect targets, potentially including untrusted third-party servers.

The attack requires user interaction, as the victim must initiate an HTTP request that triggers the vulnerable redirect-following behavior. This is a network-accessible vulnerability that can be exploited without requiring authentication, though the impact is limited to confidentiality and integrity concerns without direct availability impact.

Root Cause

The root cause stems from improper credential handling in the Reactor Netty HTTP client's redirect-following logic. When the client is configured to automatically follow HTTP redirects, it fails to properly scope or clear authentication headers when redirecting across different origins in a chain. This results in credentials being preserved and transmitted to hosts that were not the original intended recipients.

Attack Vector

An attacker can exploit this vulnerability by setting up a malicious redirect chain. The attack flow typically involves:

1. The attacker controls or compromises an initial target server or crafts a malicious link
2. When a victim application makes an authenticated request to this server with redirect-following enabled
3. The server responds with a redirect to another server (potentially attacker-controlled)
4. The Reactor Netty client follows the redirect while preserving authentication credentials
5. The attacker's final destination server receives the leaked credentials

This attack is particularly dangerous in scenarios where applications interact with user-provided URLs or when legitimate services are compromised to inject malicious redirects.

Detection Methods for CVE-2025-22227

Indicators of Compromise

• Unexpected authentication headers appearing in outbound HTTP requests to untrusted domains
• Log entries showing credential-bearing requests following redirect chains to external origins
• Authentication tokens or credentials appearing in third-party server access logs
• Anomalous cross-origin redirect patterns in application HTTP traffic

Detection Strategies

• Monitor HTTP client traffic for authentication headers being sent to unexpected destinations
• Implement network-level inspection for credential leakage across redirect boundaries
• Review application logs for redirect chains that cross security boundaries
• Analyze Reactor Netty client configurations to identify redirect-following settings

Monitoring Recommendations

• Enable detailed HTTP request logging to track redirect chains and header propagation
• Deploy network monitoring to detect credentials being sent to non-allowlisted domains
• Set up alerts for applications making authenticated requests that follow multiple redirects
• Implement application performance monitoring to identify unusual redirect patterns

How to Mitigate CVE-2025-22227

Immediate Actions Required

• Review all Reactor Netty HTTP client configurations for redirect-following settings
• Disable automatic redirect following where not explicitly required by business logic
• Implement allowlisting for redirect destinations if redirect following is necessary
• Audit applications for exposure to user-controlled URLs in HTTP client requests

Patch Information

VMware/Spring has released a security advisory for this vulnerability. Administrators should consult the Spring Security Advisory for CVE-2025-22227 for specific patching instructions and updated library versions. Apply the vendor-provided patches to Reactor Netty as soon as they become available in your dependency management system.

Workarounds

• Disable automatic redirect following in Reactor Netty HTTP client configuration
• Implement manual redirect handling with credential stripping for cross-origin redirects
• Validate redirect targets against an allowlist before following redirects
• Remove or scope authentication headers when redirect destinations change origins

If redirect following must remain enabled, consider implementing custom redirect handling that explicitly clears sensitive headers when the redirect target crosses origin boundaries. Review the Spring security advisory for additional configuration guidance specific to your deployment scenario.