CVE-2025-27505: GeoServer REST API Auth Bypass Vulnerability

CVE-2025-27505 Overview

CVE-2025-27505 is an authorization bypass vulnerability in GeoServer, an open source server that allows users to share and edit geospatial data. The vulnerability allows attackers to bypass the default REST API security configuration and access the REST API index page without proper authentication. This occurs because the REST API security filter handles the /rest path and its subpaths but fails to properly secure requests to /rest with an extension (e.g., rest.html).

Critical Impact

Unauthorized access to the REST API index can disclose sensitive information about installed extensions, potentially enabling further reconnaissance and targeted attacks against GeoServer deployments.

Affected Products

• OSGeo GeoServer versions prior to 2.26.3
• OSGeo GeoServer versions prior to 2.25.6
• Any GeoServer deployment using default REST API security configuration

Discovery Timeline

• 2025-06-10 - CVE-2025-27505 published to NVD
• 2025-08-26 - Last updated in NVD database

Technical Details for CVE-2025-27505

Vulnerability Analysis

This vulnerability stems from an incomplete URL pattern matching implementation in GeoServer's REST API security configuration. The REST API security filter is configured to protect the /rest endpoint and its subpaths (e.g., /rest/**), but the pattern matching logic does not account for requests that append a file extension directly to the /rest path itself.

When an attacker requests a URL such as /rest.html or /rest.json, the security filter fails to recognize this as a protected resource because it only matches paths that begin with /rest/. This gap in the security filter allows unauthenticated users to access the REST API index page, which can reveal information about installed GeoServer extensions and potentially expose additional attack surface.

The information disclosure aspect of this vulnerability is significant for reconnaissance purposes, as attackers can determine which extensions are installed on a GeoServer instance without authentication. This knowledge can be leveraged to identify potential secondary vulnerabilities in specific extensions.

Root Cause

The root cause is CWE-862 (Missing Authorization). The REST API security filter uses path patterns that do not adequately cover all valid URL formats that can access the REST API index. Specifically, the default configuration protects /rest and /rest/** but fails to account for path variations like /rest.html, /rest.xml, or other extension-appended variants that the application server may resolve to the same endpoint.

Attack Vector

The attack is executed over the network and requires no authentication or user interaction. An attacker can exploit this vulnerability by simply crafting HTTP requests to the vulnerable endpoint with a file extension appended:

The vulnerability can be exploited by sending a simple HTTP GET request to the GeoServer instance using a URL pattern like /geoserver/rest.html instead of /geoserver/rest. This bypasses the path-based security filter while still reaching the REST API index handler. The response reveals information about installed extensions and available REST endpoints, which would normally require authentication to access. For detailed technical information, refer to the GitHub Security Advisory.

Detection Methods for CVE-2025-27505

Indicators of Compromise

• Unusual HTTP requests to /rest.html, /rest.xml, /rest.json, or similar URL patterns in web server access logs
• Repeated unauthenticated access attempts to REST API endpoints with various file extensions
• Access log entries showing successful (HTTP 200) responses to /rest.* patterns from unknown or suspicious IP addresses
• Increased reconnaissance activity targeting GeoServer instances

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block requests matching /rest\.[a-z]+ patterns without proper authentication headers
• Configure IDS/IPS signatures to alert on access attempts to GeoServer REST API endpoints with file extensions
• Monitor HTTP access logs for requests containing /rest.html, /rest.xml, or similar patterns from unauthenticated sessions
• Deploy network traffic analysis to identify scanning activity targeting GeoServer installations

Monitoring Recommendations

• Enable detailed access logging on GeoServer and web server components to capture full request URIs
• Set up automated alerting for anomalous access patterns to REST API endpoints
• Regularly audit authentication logs for failed and unexpected successful access attempts
• Implement centralized log collection for GeoServer instances to enable correlation analysis

How to Mitigate CVE-2025-27505

Immediate Actions Required

• Upgrade GeoServer to version 2.26.3 or 2.25.6 immediately to apply the security fix
• If immediate patching is not possible, apply the configuration workaround described below
• Audit access logs for signs of exploitation before patching
• Review and restrict network access to GeoServer REST API endpoints using firewall rules

Patch Information

The vulnerability is fixed in GeoServer versions 2.26.3 and 2.25.6. Organizations should upgrade to these versions or later to fully remediate the vulnerability. The fix addresses the path pattern matching in the security configuration to properly protect all REST API access patterns. For additional details, see the GitHub Pull Request and the OSGeo Issue GEOS-11664.

Workarounds

• Modify the REST API security filter configuration to use expanded path patterns that cover extension-based access attempts
• Implement network-level access controls to restrict REST API access to trusted IP addresses only
• Deploy a reverse proxy or WAF to filter requests with suspicious URL patterns before they reach GeoServer
• Disable REST API access entirely if not required for operations

# Configuration workaround in ${GEOSERVER_DATA_DIR}/security/config.xml
# Change the paths for the rest filter to:
# /rest.*,/rest/**
# Change the paths for the gwc filter to:
# /gwc/rest.*,/gwc/rest/**
# Then restart GeoServer to apply the changes