CVE-2009-3723
📋 TL;DR
CVE-2009-3723 is an access control vulnerability in Asterisk that allows SIP calls to bypass network restrictions. Attackers can make unauthorized calls through prohibited networks. This affects Asterisk installations with network access controls configured.
💻 Affected Systems
- Asterisk
- Asterisk Business Edition
- AsteriskNOW
- TrixBox
- FreePBX
📦 What is this software?
Asterisk by Sangoma
⚠️ Risk & Real-World Impact
Worst Case
Unauthorized long-distance or premium-rate calls leading to significant financial loss, toll fraud, and potential data exfiltration through call forwarding.
Likely Case
Unauthorized local or domestic calls causing moderate financial impact and potential service disruption.
If Mitigated
Limited impact if proper network segmentation and call cost controls are implemented.
🎯 Exploit Status
Exploitation requires sending specially crafted SIP packets to bypass network restriction checks.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Asterisk 1.4.29, 1.6.0.12, Business Edition C.3.5.2
Vendor Advisory: http://downloads.asterisk.org/pub/security/AST-2009-007.html
Restart Required: Yes
Instructions:
1. Backup configuration files. 2. Upgrade to patched version using package manager or source compilation. 3. Restart Asterisk service. 4. Verify SIP/IAX functionality.
🔧 Temporary Workarounds
Network ACL Enforcement
linuxImplement network-level access controls using firewall rules to restrict SIP/IAX traffic.
iptables -A INPUT -p udp --dport 5060 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p udp --dport 5060 -j DROP
Disable Vulnerable Protocols
linuxTemporarily disable SIP or IAX protocols if not required for operations.
sed -i 's/^\[general\]/[general]\nallowguest=no/' /etc/asterisk/sip.conf
asterisk -rx 'sip reload'
🧯 If You Can't Patch
- Implement strict firewall rules to only allow SIP/IAX traffic from trusted networks
- Enable detailed call logging and monitoring for unauthorized call patterns
🔍 How to Verify
Check if Vulnerable:
Check Asterisk version: asterisk -rx 'core show version' and compare with affected versions.Check Version:
asterisk -rx 'core show version' | grep -o 'Asterisk [0-9.]\+'Verify Fix Applied:
Verify version is 1.4.29+, 1.6.0.12+, or C.3.5.2+. Test SIP calls from prohibited networks should be blocked.📡 Detection & Monitoring
Log Indicators:
- SIP/IAX calls from IP addresses in deny lists
- Unexpected call patterns or destinations
- Failed authentication attempts followed by successful calls
Network Indicators:
- SIP INVITE packets from unauthorized networks
- Unusual call volume or destinations
SIEM Query:
source="asterisk.log" ("from: " NOT (192.168.0.0/16 OR 10.0.0.0/8)) AND "INVITE"🔗 References
- http://downloads.asterisk.org/pub/security/AST-2009-007.html
- https://access.redhat.com/security/cve/cve-2009-3723
- https://security-tracker.debian.org/tracker/CVE-2009-3723
- http://downloads.asterisk.org/pub/security/AST-2009-007.html
- https://access.redhat.com/security/cve/cve-2009-3723
- https://security-tracker.debian.org/tracker/CVE-2009-3723
