cbcvebase.
CVE-2025-20333
published 2025-09-25

CVE-2025-20333: A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD)…

PriorityP197critical9.9CVSS 3.1
AVNACLPRLUINSCCHIHAH
KEVITW
CISA Known Exploited Vulnerabilitydue 2025-09-26
Exploited in the wild
EPSS
40.39%
98.5th percentile
A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to execute arbitrary code on an affected device. This vulnerability is due to improper validation of user-supplied input in HTTP(S) requests. An attacker with valid VPN user credentials could exploit this vulnerability by sending crafted HTTP requests to an affected device. A successful exploit could allow the attacker to execute arbitrary code as root, possibly resulting in the complete compromise of the affected device.

Affected

355 ranges· showing 25
VendorProductVersion rangeFixed in
ciscoadaptive_security_appliance_software>= 9.12 < 9.12.4.729.12.4.72
ciscoadaptive_security_appliance_software>= 9.14 < 9.14.4.289.14.4.28
ciscoadaptive_security_appliance_software>= 9.16 < 9.16.4.859.16.4.85
ciscoadaptive_security_appliance_software>= 9.17.0 < 9.18.4.679.18.4.67
ciscoadaptive_security_appliance_software>= 9.17.0 < 9.17.1.459.17.1.45
ciscoadaptive_security_appliance_software>= 9.18 < 9.18.4.479.18.4.47
ciscoadaptive_security_appliance_software>= 9.19 < 9.20.4.109.20.4.10
ciscoadaptive_security_appliance_software>= 9.19 < 9.19.1.379.19.1.37
ciscoadaptive_security_appliance_software>= 9.20 < 9.20.3.79.20.3.7
ciscoadaptive_security_appliance_software>= 9.22 < 9.22.2.149.22.2.14
ciscoadaptive_security_appliance_software>= 9.22 < 9.22.1.39.22.1.3
ciscoadaptive_security_appliance_software>= 9.23 < 9.23.1.199.23.1.19
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software
ciscocisco_secure_firewall_adaptive_security_appliance_software

Detection & IOCsextracted from sources · hover to see the quote

otherLINE VIPER
otherRayInitiator
sigma
dataset = cisco_asa_raw | alter alert_level = arrayindex(regextract(_raw_log, "\s%.*?(ASA\-[\d])\-[\d]{1,}\:"), 0)
  • Hunt for evidence of ROMMON modification on Cisco ASA devices, which indicates threat actor persistence across reboots and software upgrades.
  • Focus detection on Cisco ASA 5500-X series devices without secure boot enabled, as these are the primary targets for LINE VIPER and RayInitiator deployment.
  • Monitor WebVPN client authentication sessions over HTTPS and anomalous ICMP traffic with raw TCP responses from ASA devices, as LINE VIPER uses these channels for C2.
  • Use the Cortex XDR/XSIAM hunting query graphing all log types from Cisco ASA devices to identify gaps or sudden drops in log volume that may indicate logging was disabled by the threat actor.
  • Exploitation targets VPN web services on ASA/FTD; monitor for crafted HTTP(S) requests to restricted VPN URL endpoints that arrive without authentication.
  • A new attack variant (disclosed November 5, 2025) causes unexpected device reloads leading to DoS — monitor for abnormal ASA/FTD reload events on unpatched devices.
  • ·CVE-2025-20333 requires the VPN web server to be enabled on the targeted ASA/FTD device; attacks specifically targeted 5500-X Series devices with VPN web services enabled.
  • ·RayInitiator and LINE VIPER are only deployed to Cisco ASA 5500-X series devices that do not have secure boot enabled; devices with secure boot are not susceptible to this persistence mechanism.
  • ·Temporary mitigations (e.g., disabling SSL/TLS-based VPN web services) carry their own operational risks and are not a substitute for patching.
  • ·End-of-support ASA devices cannot be patched and must be permanently disconnected; CISA mandated disconnection of end-of-support devices by September 30.

CVSS provenance

nvdv3.19.9CRITICALCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
vulncheck9.9CRITICAL
cisa9.9CRITICAL
vendor_cisco9.9CRITICAL
CVEs like this are exactly what “Exploited This Week” covers.

Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.