CVE-2021-1493
📋 TL;DR
This vulnerability allows authenticated remote attackers to trigger a buffer overflow in Cisco ASA and FTD software web services interface by sending malicious HTTP requests. Successful exploitation could lead to data disclosure or denial of service through device reload. Organizations using affected Cisco security appliances with web services enabled are at risk.
💻 Affected Systems
- Cisco Adaptive Security Appliance (ASA) Software
- Cisco Firepower Threat Defense (FTD) Software
📦 What is this software?
Adaptive Security Appliance Software by Cisco
View all CVEs affecting Adaptive Security Appliance Software →
Adaptive Security Appliance Software by Cisco
View all CVEs affecting Adaptive Security Appliance Software →
Adaptive Security Appliance Software by Cisco
View all CVEs affecting Adaptive Security Appliance Software →
Adaptive Security Appliance Software by Cisco
View all CVEs affecting Adaptive Security Appliance Software →
Adaptive Security Appliance Software by Cisco
View all CVEs affecting Adaptive Security Appliance Software →
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing data exfiltration and persistent access, followed by device crash causing extended network downtime.
Likely Case
Device reload causing temporary denial of service (5-10 minutes) and potential disclosure of memory fragments containing sensitive information.
If Mitigated
Minimal impact with proper network segmentation and authentication controls limiting exploit surface.
🎯 Exploit Status
Requires authenticated access to web services interface. Exploitation requires crafting specific HTTP requests to trigger buffer overflow.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in 9.16.2, 9.17.2, 9.18.1 and later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-memc-dos-fncTyYKG
Restart Required: Yes
Instructions:
1. Download appropriate fixed software version from Cisco Software Center. 2. Backup current configuration. 3. Install update following Cisco ASA/FTD upgrade procedures. 4. Reboot device to complete installation.
🔧 Temporary Workarounds
Disable Web Services Interface
allDisable the vulnerable web services interface to prevent exploitation
no webvpn
no http server enable
Restrict Access with ACLs
allLimit access to web services interface to trusted management networks only
access-list WEBVPN_ACL permit ip <trusted_network> any
access-group WEBVPN_ACL in interface <interface_name>
🧯 If You Can't Patch
- Implement strict network segmentation to isolate ASA/FTD management interfaces
- Enforce strong authentication and limit administrative accounts with web services access
🔍 How to Verify
Check if Vulnerable:
Check ASA/FTD version with 'show version' and compare against affected versions. Verify web services are enabled with 'show running-config | include webvpn|http server'.Check Version:
show version | include VersionVerify Fix Applied:
After patching, verify version is 9.16.2+, 9.17.2+, or 9.18.1+ with 'show version'. Confirm patch applied by checking Cisco advisory for specific fixed versions.📡 Detection & Monitoring
Log Indicators:
- Multiple HTTP requests to web services interface from single source
- Device reload events without administrative action
- Memory allocation errors in system logs
Network Indicators:
- Unusual HTTP traffic patterns to ASA/FTD management interfaces
- Large or malformed HTTP requests to web services port
SIEM Query:
source="asa_logs" AND ("webvpn" OR "http server") AND ("buffer overflow" OR "reload" OR "crash")