CVE-2025-12543
📋 TL;DR
CVE-2025-12543 is a critical vulnerability in Undertow HTTP server core where improper Host header validation allows attackers to poison caches, perform internal network scans, or hijack user sessions. This affects Java applications using Undertow, including WildFly and JBoss EAP deployments.
💻 Affected Systems
- Undertow HTTP server
- WildFly
- JBoss EAP
- Other Java applications using Undertow
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Attackers could hijack user sessions, poison web caches to serve malicious content, and perform internal network reconnaissance leading to full system compromise.
Likely Case
Cache poisoning attacks leading to credential theft or malware distribution, and internal network scanning to identify additional targets.
If Mitigated
Limited impact with proper network segmentation, WAF filtering, and monitoring in place.
🎯 Exploit Status
Exploitation requires sending HTTP requests with malicious Host headers, which is trivial for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Undertow 2.3.40.Final or later
Vendor Advisory: https://access.redhat.com/security/cve/CVE-2025-12543
Restart Required: Yes
Instructions:
1. Update Undertow to version 2.3.40.Final or later. 2. Update WildFly or JBoss EAP to versions containing the patched Undertow. 3. Restart affected Java applications.
🔧 Temporary Workarounds
WAF Host Header Validation
allConfigure web application firewall to reject HTTP requests with malformed or suspicious Host headers.
Reverse Proxy Filtering
allDeploy reverse proxy (nginx, Apache) to validate and sanitize Host headers before reaching Undertow.
🧯 If You Can't Patch
- Implement strict network segmentation to limit access to vulnerable systems
- Deploy intrusion detection systems to monitor for suspicious Host header patterns
🔍 How to Verify
Check if Vulnerable:
Check Undertow version in application dependencies or server configuration files. Versions below 2.3.40.Final are vulnerable.Check Version:
Check application's pom.xml, build.gradle, or server logs for Undertow version information.Verify Fix Applied:
Verify Undertow version is 2.3.40.Final or later after patching and restart.📡 Detection & Monitoring
Log Indicators:
- HTTP requests with unusual Host headers
- Multiple requests with varying Host headers from single source
Network Indicators:
- HTTP traffic with malformed Host headers
- Unusual cache-related requests
SIEM Query:
source.ip="*" AND http.host CONTAINS "malicious_pattern" OR http.host LENGTH > 100🔗 References
- https://access.redhat.com/errata/RHSA-2026:0383
- https://access.redhat.com/errata/RHSA-2026:0384
- https://access.redhat.com/errata/RHSA-2026:0386
- https://access.redhat.com/errata/RHSA-2026:3889
- https://access.redhat.com/errata/RHSA-2026:3890
- https://access.redhat.com/errata/RHSA-2026:3891
- https://access.redhat.com/errata/RHSA-2026:3892
- https://access.redhat.com/security/cve/CVE-2025-12543
- https://bugzilla.redhat.com/show_bug.cgi?id=2408784
