CVE-2025-20333 Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense: memory-safety flaw
In plain words: The program mishandles the memory it uses to keep track of data. A specially made input can scramble that memory. Usually lets an attacker crash the program or run their own code with its permissions.
Confirmed exploited by CISA on · US federal patch deadline Sep 26, 2025
What to do
- Install Cisco's security update for Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Patch edge devices first — attackers often start scanning for them within hours of a fix.
- Never expose the device's admin page to the internet.
- After patching a device that was exposed, follow the vendor's compromise checks, end active sessions and change passwords.
Who is affected
Work IT. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.
What's at risk: They face the internet and guard the whole network, so a flaw here can hand attackers a way in — and these devices usually run no antivirus, so break-ins go unnoticed.
The details
- Official name
- Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Vulnerability
- Product
- Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense
- CISA description
- Cisco Secure Firewall Adaptive Security (ASA) Appliance and Secure Firewall Threat Defense (FTD) Software VPN Web Server contain a buffer overflow vulnerability that allows for remote code execution. This vulnerability could be chained with CVE-2025-20362.
- Type of flaw
- Memory-safety flaw (CWE-120)
- Confirmed exploited
- Sep 25, 2025
- US federal patch deadline
- Sep 26, 2025
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Answering about CVE-2025-20333 ·
Questions about CVE-2025-20333
Is CVE-2025-20333 being exploited?
Yes. CISA added CVE-2025-20333 to its Known Exploited Vulnerabilities catalog on Sep 25, 2025, which means there is reliable evidence of real-world attacks.
How do I fix CVE-2025-20333?
Install Cisco's security update for Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense. If no update exists, follow the vendor's workaround or stop using the product until one ships. Patch edge devices first — attackers often start scanning for them within hours of a fix.
Am I affected by CVE-2025-20333?
Only if you use Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.