CVE-2023-26513
📋 TL;DR
CVE-2023-26513 is an excessive iteration vulnerability in Apache Sling Resource Merger that allows attackers to cause denial of service through resource exhaustion. This affects Apache Sling deployments using Resource Merger from version 1.2.0 up to (but not including) 1.4.2. The vulnerability can be triggered by sending specially crafted requests to vulnerable endpoints.
💻 Affected Systems
- Apache Sling Resource Merger
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability due to resource exhaustion (CPU/memory consumption), potentially affecting all users of the application.
Likely Case
Degraded performance or temporary service disruption for affected endpoints, requiring restart of the Sling instance.
If Mitigated
Minimal impact with proper rate limiting, resource quotas, and network segmentation in place.
🎯 Exploit Status
Exploitation requires sending crafted HTTP requests to vulnerable endpoints. No authentication is required, making exploitation straightforward.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.4.2
Vendor Advisory: https://lists.apache.org/thread/xpcpo1y88ldss5hgmvogsf6h3735l5zb
Restart Required: Yes
Instructions:
1. Download Apache Sling Resource Merger version 1.4.2 or later. 2. Replace the existing resource-merger bundle in your Sling instance. 3. Restart the Apache Sling instance to apply the update.
🔧 Temporary Workarounds
Rate Limiting
allImplement request rate limiting on Apache Sling endpoints to prevent excessive iteration attacks
# Configure via Apache HTTPD mod_evasive or similar
# Example: mod_evasive configuration in httpd.conf
Network Access Control
linuxRestrict access to Apache Sling endpoints to trusted networks only
# Use firewall rules to limit access
iptables -A INPUT -p tcp --dport 8080 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP
🧯 If You Can't Patch
- Implement strict rate limiting and request validation on all Apache Sling endpoints
- Deploy web application firewall (WAF) rules to detect and block excessive iteration patterns
🔍 How to Verify
Check if Vulnerable:
Check the version of the Apache Sling Resource Merger bundle in your Sling instance. If version is >=1.2.0 and <1.4.2, you are vulnerable.Check Version:
Check Sling web console at /system/console/bundles or use: curl -u admin:admin http://localhost:8080/system/console/bundles | grep 'Apache Sling Resource Merger'Verify Fix Applied:
Verify that Apache Sling Resource Merger bundle version is 1.4.2 or higher after patching.📡 Detection & Monitoring
Log Indicators:
- Unusually high number of requests to resource merger endpoints
- Increased CPU/memory usage patterns
- Request timeouts or 503 errors
Network Indicators:
- High volume of HTTP requests to /apps/, /libs/, or other resource paths
- Requests with deep path traversal patterns
SIEM Query:
source="apache-sling" AND (uri_path="/apps/*" OR uri_path="/libs/*") AND request_count > 1000 per minute