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CVE-2026-20039 is a denial-of-service vulnerability in the VPN web server component of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software. The flaw is caused by ineffective memory management in the VPN web server. A remote, unauthenticated attacker can trigger the issue by sending a large number of crafted HTTP requests to an affected device. Successful exploitation can force the device to reload, interrupting VPN web server availability and associated services.
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
If you can’t patch tonight, do this now.
Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
15 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Unauthenticated remote denial-of-service vulnerability in the VPN web server component of Cisco Secure Firewall ASA and Cisco Secure Firewall Threat Defense (FTD), triggered by high volumes of crafted HTTP requests leading to device reload due to ineffective memory management.
Denial of service vulnerability in the VPN web server component of Cisco ASA and Cisco Secure Firewall Threat Defense (FTD).
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.