CVE-2020-25583
📋 TL;DR
This is a critical buffer overflow vulnerability in FreeBSD's rtsold IPv6 router advertisement daemon. Attackers can exploit it by sending malicious DNSSL options to trigger remote code execution or denial of service. Systems running vulnerable FreeBSD versions with rtsold enabled are affected.
💻 Affected Systems
- FreeBSD
📦 What is this software?
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with root privileges leading to complete system compromise
Likely Case
Denial of service through rtsold crash or potential remote code execution
If Mitigated
Limited impact if rtsold is disabled or network access is restricted
🎯 Exploit Status
Exploitation requires sending specially crafted IPv6 router advertisements with malicious DNSSL options
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FreeBSD 12.2-STABLE r368250+, 11.4-STABLE r368253+, 12.2-RELEASE p1+, 12.1-RELEASE p11+, 11.4-RELEASE p5+
Vendor Advisory: https://security.FreeBSD.org/advisories/FreeBSD-SA-20:32.rtsold.asc
Restart Required: Yes
Instructions:
1. Update FreeBSD using freebsd-update or source update. 2. Apply the relevant patch for your version. 3. Restart the system or rtsold service.
🔧 Temporary Workarounds
Disable rtsold service
allStop and disable the rtsold daemon if IPv6 router advertisement functionality is not required
service rtsold stop
service rtsold disable
Block IPv6 router advertisements
linuxConfigure firewall to block incoming IPv6 router advertisements (ICMPv6 type 134)
ip6tables -A INPUT -p icmpv6 --icmpv6-type 134 -j DROP
🧯 If You Can't Patch
- Disable rtsold service immediately
- Implement network segmentation to restrict access to affected systems
🔍 How to Verify
Check if Vulnerable:
Check FreeBSD version with 'uname -a' and verify if rtsold is running with 'ps aux | grep rtsold'Check Version:
uname -aVerify Fix Applied:
Verify FreeBSD version is patched and rtsold service is either updated or disabled📡 Detection & Monitoring
Log Indicators:
- rtsold crash logs in /var/log/messages
- kernel panic messages related to buffer overflow
Network Indicators:
- Unusual IPv6 router advertisement traffic
- Multiple malformed DNSSL options
SIEM Query:
source="freebsd" AND (process="rtsold" AND (event="crash" OR event="segfault"))