CVE-2021-1223
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to bypass HTTP file policy controls on affected Cisco devices by sending crafted HTTP packets with specific range headers. It affects multiple Cisco products using vulnerable Snort detection engine versions. Successful exploitation could enable delivery of malicious payloads that would normally be blocked.
💻 Affected Systems
- Cisco Firepower Threat Defense
- Cisco Firepower Management Center
- Cisco Adaptive Security Appliance
- Other Cisco products using Snort detection engine
📦 What is this software?
Ios Xe by Cisco
Cisco IOS XE is Cisco's modern network operating system running on enterprise routers, switches, and wireless controllers deployed across corporate networks, data centers, branch offices, and service provider infrastructure worldwide. As the evolution of Cisco IOS, IOS XE provides a Linux-based modu...
Learn more about Ios Xe →Secure Firewall Management Center by Cisco
Secure Firewall Management Center by Cisco
Secure Firewall Management Center by Cisco
Snort by Snort
⚠️ Risk & Real-World Impact
Worst Case
Attackers deliver malware, ransomware, or other malicious files through HTTP traffic that should have been blocked, potentially leading to full system compromise.
Likely Case
Attackers bypass file filtering to deliver malicious scripts or executables, enabling initial foothold for further attacks.
If Mitigated
With proper network segmentation and additional security controls, impact is limited to potential policy bypass without direct system compromise.
🎯 Exploit Status
Exploitation requires sending HTTP traffic through affected devices. No authentication needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Multiple fixed versions depending on product - see Cisco advisory for specific versions
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-snort-filepolbypass-67DEwMe2
Restart Required: Yes
Instructions:
1. Identify affected Cisco devices. 2. Check Cisco advisory for specific fixed versions for your products. 3. Apply appropriate patches/updates. 4. Restart affected services/devices as required.
🔧 Temporary Workarounds
Disable HTTP inspection
allTemporarily disable HTTP inspection/file policy on affected devices to prevent exploitation
Device-specific configuration commands - refer to Cisco documentation
Network segmentation
allIsolate affected devices or restrict HTTP traffic to/from vulnerable systems
🧯 If You Can't Patch
- Implement strict network segmentation to limit exposure of affected devices
- Deploy additional security controls like web application firewalls or proxy servers in front of vulnerable devices
🔍 How to Verify
Check if Vulnerable:
Check device version against Cisco advisory. For Firepower: show version | include VersionCheck Version:
show version (Cisco devices)Verify Fix Applied:
Verify installed version matches or exceeds patched versions listed in Cisco advisory📡 Detection & Monitoring
Log Indicators:
- HTTP requests with unusual range headers
- File policy bypass alerts
- Unexpected file transfers through HTTP
Network Indicators:
- HTTP traffic with crafted range headers bypassing expected filters
- Unusual file types/sizes in HTTP transfers
SIEM Query:
http.request.header:"range" AND (http.request.header:"bytes=0-*" OR unusual_range_patterns)🔗 References
- https://lists.debian.org/debian-lts-announce/2023/02/msg00011.html
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-snort-filepolbypass-67DEwMe2
- https://www.debian.org/security/2023/dsa-5354
- https://lists.debian.org/debian-lts-announce/2023/02/msg00011.html
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-snort-filepolbypass-67DEwMe2
- https://www.debian.org/security/2023/dsa-5354
