CVE-2026-2376: Mirror-Registry SSRF Vulnerability

CVE-2026-2376 Overview

A Server-Side Request Forgery (SSRF) vulnerability has been identified in mirror-registry that allows authenticated users to manipulate the application into accessing unintended internal or restricted systems. The flaw exists in how the application handles URL processing, specifically when following HTTP redirects without proper validation of the final destination.

When the application processes user-supplied web addresses, it automatically follows redirects without verifying whether the final destination is an authorized endpoint. This behavior enables attackers to route requests through the mirror-registry application to internal systems, cloud metadata services, or other restricted network resources that should not be accessible from external interfaces.

Critical Impact

Authenticated attackers can exploit this SSRF vulnerability to access internal network resources, potentially exposing sensitive configuration data, cloud instance metadata, or other protected services behind the network perimeter.

Affected Products

• mirror-registry (specific versions not disclosed)
• Red Hat Quay (related component)

Discovery Timeline

• 2026-03-12 - CVE-2026-2376 published to NVD
• 2026-03-12 - Last updated in NVD database

Technical Details for CVE-2026-2376

Vulnerability Analysis

This vulnerability is classified as CWE-601 (URL Redirection to Untrusted Site / Open Redirect), though the actual exploitation pattern aligns with SSRF attack methodology. The core issue stems from insufficient validation when the mirror-registry application processes URLs provided by authenticated users.

The application's HTTP client follows redirects automatically without implementing proper safeguards to verify that redirect destinations fall within allowed network boundaries. An attacker can craft a malicious URL that initially points to an external server under their control, which then issues a redirect response pointing to an internal resource such as http://169.254.169.254/latest/meta-data/ (cloud metadata endpoint) or internal service endpoints.

Since the redirect is processed server-side by the mirror-registry application, the final request originates from the server's network context, bypassing firewall rules and network segmentation that would normally prevent external access to these resources.

Root Cause

The root cause is the lack of redirect destination validation in the HTTP client configuration. When processing user-supplied URLs, the application fails to:

1. Validate that redirect destinations match an allowlist of permitted hosts
2. Block redirects to private IP address ranges (RFC 1918 addresses)
3. Prevent redirects to link-local addresses used by cloud metadata services
4. Limit the number of redirects or inspect intermediate destinations

This creates an open conduit for attackers to proxy requests through the application to otherwise inaccessible internal systems.

Attack Vector

The attack requires authentication to the mirror-registry system but does not require elevated privileges. An attacker with valid credentials can submit requests containing malicious URLs that redirect to internal targets.

The vulnerability is accessible over the network, and while the attack has some complexity due to the need to set up a redirect server, the exploitation technique is well-documented and commonly used in SSRF attacks.

A typical attack flow involves the attacker providing a URL like https://attacker.com/redirect which returns an HTTP 302 redirect to http://internal-service.local:8080/api/sensitive-data. The mirror-registry application follows this redirect transparently, fetching internal data and potentially returning it to the attacker.

Detection Methods for CVE-2026-2376

Indicators of Compromise

• Unusual outbound requests from the mirror-registry server to internal IP ranges or localhost addresses
• HTTP requests to cloud metadata service endpoints (e.g., 169.254.169.254, fd00:ec2::254)
• Requests to mirror-registry with URLs pointing to external servers known for redirect-based attacks
• Log entries showing redirects from external hosts to internal network addresses

Detection Strategies

• Monitor mirror-registry logs for requests containing URLs with suspicious redirect chains
• Implement network-level detection for requests from the mirror-registry server to private IP ranges or metadata endpoints
• Deploy application-level logging to capture the full URL resolution path including all redirect hops
• Alert on requests from mirror-registry to services that should not be accessible from the application tier

Monitoring Recommendations

• Enable verbose HTTP client logging to capture redirect behavior and final destination URLs
• Implement egress filtering and log all outbound connections from mirror-registry servers
• Set up alerts for any connections to RFC 1918 private address ranges from the application
• Monitor for unusual patterns in authenticated user requests, particularly those containing external URLs

How to Mitigate CVE-2026-2376

Immediate Actions Required

• Review and restrict outbound network access from mirror-registry servers using firewall rules
• Block access to cloud metadata service IP addresses (169.254.169.254) from application servers
• Implement URL allowlisting for any features that accept user-provided URLs
• Audit logs for any evidence of SSRF exploitation attempts
• Consider implementing a web application firewall (WAF) rule to detect SSRF patterns

Patch Information

Red Hat has acknowledged this vulnerability and a fix is being tracked. Refer to the Red Hat CVE-2026-2376 Advisory for the latest patch availability information. The related fix can be reviewed in GitHub Quay Pull Request #5074.

Additional technical details and patch status updates are available in Red Hat Bug Report #2439117.

Workarounds

• Disable automatic redirect following in the HTTP client configuration if operationally feasible
• Implement a proxy layer that validates all outbound requests from mirror-registry before execution
• Use network segmentation to isolate mirror-registry servers and restrict their access to internal services
• Configure egress firewall rules to block connections from application servers to private IP ranges and cloud metadata endpoints
• Deploy application-layer controls to validate and sanitize all user-provided URLs before processing