CVE-2023-27900
📋 TL;DR
This vulnerability in Jenkins allows attackers to cause denial of service by exploiting improper request handling in the Apache Commons FileUpload library. Attackers can send specially crafted multipart requests to exhaust server resources. All Jenkins instances running affected versions are vulnerable.
💻 Affected Systems
- Jenkins
📦 What is this software?
Jenkins by Jenkins
Jenkins by Jenkins
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability due to resource exhaustion, potentially requiring server restart and causing extended downtime.
Likely Case
Temporary service degradation or unavailability until malicious requests stop or server is restarted.
If Mitigated
Minimal impact with proper request filtering and resource monitoring in place.
🎯 Exploit Status
Exploitation requires sending specially crafted HTTP requests but does not require authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Jenkins 2.394, LTS 2.375.4
Vendor Advisory: https://www.jenkins.io/security/advisory/2023-03-08/#SECURITY-3030
Restart Required: Yes
Instructions:
1. Backup Jenkins configuration and data. 2. Upgrade to Jenkins 2.394 or LTS 2.375.4. 3. Restart Jenkins service. 4. Verify upgrade completed successfully.
🔧 Temporary Workarounds
Request Filtering
allImplement web application firewall or reverse proxy rules to limit multipart request size and part count.
Resource Limits
allConfigure system resource limits and monitoring to detect and mitigate resource exhaustion attacks.
🧯 If You Can't Patch
- Implement strict network segmentation to limit access to Jenkins instances
- Deploy web application firewall with request size and rate limiting rules
🔍 How to Verify
Check if Vulnerable:
Check Jenkins version via Manage Jenkins > About Jenkins or via CLI with 'java -jar jenkins.war --version'Check Version:
java -jar jenkins.war --versionVerify Fix Applied:
Verify version is 2.394 or higher (or LTS 2.375.4 or higher) and test multipart upload functionality.📡 Detection & Monitoring
Log Indicators:
- Unusually large number of multipart requests
- OutOfMemory errors in Jenkins logs
- High CPU/memory usage spikes
Network Indicators:
- Large volume of POST requests to Jenkins endpoints
- Abnormal request patterns with many multipart parts
SIEM Query:
source="jenkins.log" AND ("OutOfMemory" OR "java.lang.OutOfMemoryError")