CVE-2019-14513
📋 TL;DR
CVE-2019-14513 is a buffer overflow vulnerability in Dnsmasq DNS server software caused by improper bounds checking when processing large DNS packets. Attackers controlling a DNS server can send specially crafted packets to trigger memory corruption, potentially leading to denial of service or remote code execution. This affects all systems running Dnsmasq versions before 2.76.
💻 Affected Systems
- Dnsmasq
📦 What is this software?
Dnsmasq by Thekelleys
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with root privileges, allowing complete system compromise and potential lateral movement within the network.
Likely Case
Denial of service causing DNS service disruption, potentially affecting network connectivity and dependent services.
If Mitigated
Limited impact with proper network segmentation and DNS server isolation, potentially only causing service disruption.
🎯 Exploit Status
Exploitation requires control of a DNS server that the vulnerable Dnsmasq instance queries. Public proof-of-concept demonstrates triggering the overflow.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.76 and later
Vendor Advisory: https://lists.debian.org/debian-lts-announce/2019/09/msg00013.html
Restart Required: Yes
Instructions:
1. Update Dnsmasq to version 2.76 or later using your distribution's package manager. 2. For Debian/Ubuntu: sudo apt update && sudo apt install dnsmasq. 3. For Red Hat/CentOS: sudo yum update dnsmasq. 4. Restart Dnsmasq service: sudo systemctl restart dnsmasq.
🔧 Temporary Workarounds
Limit DNS packet size
linuxConfigure Dnsmasq to reject DNS packets larger than typical size to prevent triggering the overflow
Add 'edns-packet-max=512' to /etc/dnsmasq.conf
Restart dnsmasq: sudo systemctl restart dnsmasq
Disable DNS forwarding
linuxConfigure Dnsmasq to only serve local DNS and not forward queries to upstream servers
Set 'no-resolv' and 'no-forward' in /etc/dnsmasq.conf
Restart dnsmasq: sudo systemctl restart dnsmasq
🧯 If You Can't Patch
- Implement network segmentation to isolate Dnsmasq servers from untrusted networks
- Use firewall rules to restrict which DNS servers Dnsmasq can communicate with
🔍 How to Verify
Check if Vulnerable:
Check Dnsmasq version: dnsmasq --version | head -1. If version is below 2.76, system is vulnerable.Check Version:
dnsmasq --version | head -1Verify Fix Applied:
After update, verify version is 2.76 or higher: dnsmasq --version | head -1📡 Detection & Monitoring
Log Indicators:
- DNS query failures
- Dnsmasq crash logs
- Memory corruption errors in system logs
Network Indicators:
- Unusually large DNS packets (over 512 bytes)
- DNS traffic from unexpected sources
SIEM Query:
source="dnsmasq" AND ("segmentation fault" OR "buffer overflow" OR "crash")