Exploitation of Cisco ASA and FTD Zero-Day Vulnerabilities by Storm-1849
Cisco confirmed that attackers have been actively exploiting two zero-day vulnerabilities, CVE-2025-20333 and CVE-2025-20362, in Cisco Secure Firewall Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) software. These vulnerabilities allow attackers to execute arbitrary code as root and access restricted URLs without authentication, leading to device reloads and denial-of-service (DoS) conditions. The U.K. National Cyber Security Centre (NCSC) and Cisco have linked these exploits to malware campaigns involving RayInitiator and LINE VIPER, and have urged immediate patching. Security advisories highlight that unpatched devices are at risk of persistent compromise, and recommend comprehensive remediation steps including patching, forensic analysis, and resetting credentials.
Threat intelligence reports attribute the exploitation campaign to the China-linked group Storm-1849 (ArcaneDoor), which targeted U.S. financial institutions, defense contractors, and military organizations throughout October. Despite public disclosure and patch directives from CISA, attacks continued, demonstrating the attackers' operational sophistication and persistence. Experts warn that organizations running unpatched ASA devices should assume compromise and prioritize forensic hunting for ROM-level malware, as well as implement robust monitoring and maintenance practices to mitigate ongoing risks.
Timeline
Apr 24, 2026
CISA orders federal malware checks and Firepower inventories
CISA, working with the U.K. NCSC, directed federal agencies to verify malware checks on affected Cisco devices by April 24, 2026 and submit Cisco Firepower device inventories by May 1. The advisory warned that persistence may remain even after patching and told agencies not to disconnect affected devices unless instructed by CISA.
Apr 23, 2026
CISA confirms FIRESTARTER compromise at U.S. FCEB agency
CISA and the U.K. NCSC reported that APT actors used the FIRESTARTER backdoor on publicly exposed Cisco Firepower and Secure Firewall ASA/FTD devices after exploiting CVE-2025-20333 and/or CVE-2025-20362. CISA said it observed a successful implant in the wild on a Cisco Firepower device at a U.S. FCEB agency and warned the malware can survive firmware updates and patching, requiring deeper remediation than patching alone.
Apr 23, 2026
Talos identifies FIRESTARTER backdoor in ArcaneDoor Firepower attacks
Cisco Talos reported that UAT-4356/ArcaneDoor continued targeting Cisco Firepower devices running FXOS using CVE-2025-20333 and CVE-2025-20362, deploying a custom backdoor called FIRESTARTER. Talos said the implant enables remote access and arbitrary code execution in the LINA process, overlaps technically with RayInitiator Stage 3 shellcode, and uses transient persistence removable by hard reboot.
Apr 23, 2026
Cisco warns of evolved persistence mechanism on ASA and FTD devices
Cisco published a new security advisory describing the continued evolution of the persistence mechanism used against Secure Firewall ASA and FTD devices. The advisory indicates the campaign developed beyond previously disclosed ArcaneDoor persistence techniques and represents a new stage in Cisco's public reporting on the threat.
Nov 6, 2025
Cisco releases additional fixes for Unified CCX and ISE flaws
Cisco also patched two critical Unified Contact Center Express vulnerabilities, CVE-2025-20354 and CVE-2025-20358, and a high-severity denial-of-service flaw in Identity Services Engine. The company said it had no evidence these additional vulnerabilities were exploited in the wild and urged customers to update promptly.
Nov 6, 2025
Cisco links new firewall activity to ArcaneDoor with high confidence
Cisco assessed with high confidence that the newly observed ASA/FTD attack activity is related to the ArcaneDoor threat actor, also referenced as UAT4356 or Storm-1849 in reporting. Cisco said it had no evidence that other FTD or hardware platforms had been successfully compromised.
Nov 6, 2025
Cisco discloses new ASA/FTD attack variant causing device reloads
Cisco announced a new attack variant against vulnerable Secure Firewall ASA and FTD devices using CVE-2025-20333 and CVE-2025-20362. The company warned the activity could trigger unexpected reloads and denial-of-service conditions on unpatched systems and urged upgrades to fixed releases.
Oct 1, 2025
Storm-1849 targets Cisco ASA devices throughout October
During October 2025, the China-linked group Storm-1849 targeted vulnerable Cisco ASA firewalls, focusing on U.S. financial institutions, defense contractors, and military organizations. The campaign reportedly paused only during China's Golden Week holiday despite prior patching guidance.
Sep 26, 2025
Bootkit persistence and anti-forensics disclosed in Cisco ASA campaign
Reporting on the Cisco zero-day campaign said the suspected China-linked actor deployed a firmware/ROM bootkit on Cisco ASA and Firepower devices, enabling persistence that could survive reboots and even patching. The malware also reportedly included anti-forensic behavior that rebooted devices when analysts used tab-completion for certain CLI commands, complicating investigation and remediation.
Sep 25, 2025
CISA orders patching of exploited Cisco firewall flaws
In late September 2025, CISA directed organizations to patch CVE-2025-20333 and CVE-2025-20362 after the vulnerabilities were identified as actively exploited. The flaws were also added to the Known Exploited Vulnerabilities catalog.
Sep 1, 2025
U.S. and U.K. agencies link zero-days to RayInitiator and LINE VIPER
Government reporting, including from the U.K. NCSC, said the two Cisco flaws were exploited as zero-days to deploy the RayInitiator and LINE VIPER malware families. The malware enabled persistence, command-and-control, traffic capture, and other post-compromise capabilities on Cisco ASA devices.
May 1, 2025
ArcaneDoor activity against Cisco ASA begins
Cisco firewall attacks tied to the ArcaneDoor campaign were reported as ongoing since May 2025, involving exploitation of CVE-2025-20333 and CVE-2025-20362 as zero-days. The activity included malware deployment and persistent compromise of affected devices.
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