CVE-2019-13273
📋 TL;DR
CVE-2019-13273 is a critical buffer overflow vulnerability in Xymon's csvinfo CGI script that allows remote code execution. Attackers can exploit it by sending a specially crafted GET request with a malicious srcdb parameter. All Xymon installations through version 4.3.28 are affected.
💻 Affected Systems
- Xymon
📦 What is this software?
Xymon by Xymon
⚠️ Risk & Real-World Impact
Worst Case
Remote attacker gains full control of the Xymon server, potentially leading to complete system compromise, data theft, and lateral movement within the network.
Likely Case
Remote code execution with the privileges of the Xymon web server process, allowing installation of backdoors, data exfiltration, or use as a pivot point.
If Mitigated
If proper network segmentation and least privilege are implemented, impact may be limited to the Xymon server itself.
🎯 Exploit Status
Exploitation requires sending a crafted HTTP GET request to the csvinfo script. No authentication is required.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.3.29 and later
Vendor Advisory: https://lists.debian.org/debian-lts-announce/2019/08/msg00032.html
Restart Required: Yes
Instructions:
1. Upgrade Xymon to version 4.3.29 or later. 2. Restart the Xymon service. 3. Verify the csvinfo script has been updated.
🔧 Temporary Workarounds
Disable csvinfo CGI script
linuxRemove or disable access to the vulnerable csvinfo CGI script
mv /usr/lib/xymon/cgi-bin/csvinfo /usr/lib/xymon/cgi-bin/csvinfo.disabled
chmod 000 /usr/lib/xymon/cgi-bin/csvinfo.disabled
Network access control
linuxRestrict network access to Xymon web interface using firewall rules
iptables -A INPUT -p tcp --dport 80 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Xymon servers from critical systems
- Deploy web application firewall (WAF) rules to block requests with suspicious srcdb parameters
🔍 How to Verify
Check if Vulnerable:
Check Xymon version: xymon --version. If version is 4.3.28 or earlier, system is vulnerable.Check Version:
xymon --versionVerify Fix Applied:
Verify Xymon version is 4.3.29 or later and check that csvinfo script has been updated with proper bounds checking.📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP GET requests to /xymon/cgi-bin/csvinfo with long srcdb parameters
- Failed buffer overflow attempts in web server logs
Network Indicators:
- HTTP requests to csvinfo endpoint with unusually long query strings
- Traffic patterns suggesting exploitation attempts
SIEM Query:
source="web_server_logs" AND uri="/xymon/cgi-bin/csvinfo" AND query_string="*srcdb=*" AND length(query_string)>100