CVE-2020-7461
📋 TL;DR
A heap overflow vulnerability in FreeBSD's dhclient allows remote attackers to potentially execute arbitrary code by sending malformed DHCP option 119 packets. This affects FreeBSD systems running vulnerable versions of dhclient, which typically runs with reduced privileges in a sandbox, limiting the impact. Systems using DHCP for network configuration are at risk.
💻 Affected Systems
- FreeBSD dhclient
📦 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
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Freebsd by Freebsd
Freebsd by Freebsd
Freebsd by Freebsd
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to privilege escalation, network compromise, or persistence on affected systems, though sandboxing reduces impact.
Likely Case
Denial of service (dhclient crash) causing network connectivity loss until dhclient restarts or system reboots.
If Mitigated
Limited impact due to Capsicum sandbox and reduced privileges, potentially only denial of service.
🎯 Exploit Status
Exploitation requires sending malformed DHCP packets to the vulnerable dhclient. The Capsicum sandbox makes reliable exploitation more difficult.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FreeBSD 12.1-STABLE r365010+, 11.4-STABLE r365011+, 12.1-RELEASE p9+, 11.4-RELEASE p3+, 11.3-RELEASE p13+
Vendor Advisory: https://security.FreeBSD.org/advisories/FreeBSD-SA-20:26.dhclient.asc
Restart Required: Yes
Instructions:
1. Update FreeBSD system using 'freebsd-update fetch' and 'freebsd-update install'. 2. Rebuild dhclient from ports if using custom build. 3. Restart network services or reboot system.
🔧 Temporary Workarounds
Disable DHCP client
freebsdConfigure system with static IP addresses instead of using DHCP
Edit /etc/rc.conf to set ifconfig_<interface>="inet <static_ip> netmask <netmask>"
Restart networking: /etc/rc.d/netif restart
Use alternative DHCP client
freebsdReplace vulnerable dhclient with alternative DHCP client implementation
Install dhcpcd or other DHCP client from ports/pkg
Configure to use alternative client in /etc/rc.conf
🧯 If You Can't Patch
- Isolate affected systems on separate VLANs with strict network segmentation
- Implement DHCP snooping on network switches to filter malicious DHCP packets
🔍 How to Verify
Check if Vulnerable:
Check FreeBSD version with 'uname -a' and compare against affected versions. Check if dhclient is running with 'ps aux | grep dhclient'.Check Version:
uname -aVerify Fix Applied:
Verify FreeBSD version is patched with 'uname -a'. Check dhclient binary version if custom built.📡 Detection & Monitoring
Log Indicators:
- dhclient crashes or abnormal termination in system logs
- Network connectivity loss events coinciding with DHCP traffic
Network Indicators:
- Malformed DHCP packets with option 119 in network traffic
- Unusual DHCP traffic patterns from untrusted sources
SIEM Query:
source="system_logs" dhclient AND (crash OR error OR terminated)