Cisco Flaw Affects Firewalls

A vulnerability in the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to conduct directory traversal attacks and obtain read and delete access to sensitive files on a targeted system. The vulnerability is due to a lack of proper input validation of the HTTP URL. An attacker could exploit this vulnerability by sending a crafted HTTP request containing directory traversal character sequences. An exploit could allow the attacker to view or delete arbitrary files on the targeted system. When the device is reloaded after exploitation of this vulnerability, any files that were deleted are restored. The attacker can only view and delete files within the web services file system. This file system is enabled when the affected device is configured with either WebVPN or AnyConnect features. This vulnerability can not be used to obtain access to ASA or FTD system files or underlying operating system (OS) files. Reloading the affected device will restore all files within the web services file system.

CVE-2020-3259 is an information-disclosure vulnerability in the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software, caused by a buffer-tracking error when the device parses invalid URLs. An unauthenticated, remote attacker can trigger it by sending a crafted GET request to the web services interface, which allows retrieval of the device's memory contents and disclosure of confidential information. Only devices with specific AnyConnect and WebVPN configurations are affected, but those configurations are common on ASA/FTD firewalls deployed as enterprise edge and remote-access VPN gateways. Exploitation is confirmed in the wild: CISA added the bug to its Known Exploited Vulnerabilities catalog on 2024-02-15 with known ransomware use, and the Akira ransomware group (which the FBI says has extorted $42 million across roughly 250 attacks since March 2023) is actively exploiting it, with LockBit also scanning for vulnerable Cisco ASA devices. EPSS assigns a 71.8% probability of exploitation within 30 days, and no public proof-of-concept code is known.

Do: Upgrade affected ASA and FTD devices to the fixed releases listed in Cisco's security advisory for CVE-2020-3259; if patching is delayed, disable or restrict the web services interface (WebVPN/AnyConnect) to trusted source networks. Per the CISA KEV required action, apply vendor mitigations or discontinue use where mitigations are unavailable. Prioritize internet-facing VPN gateways and hunt for exploitation indicators (anomalous GET requests to the web services interface) given active Akira and LockBit targeting.

Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) contain an improper input validation flaw (CWE-20) in how HTTP requests process URLs. An attacker triggers it by sending a crafted HTTP request containing directory traversal character sequences to the web services interface of an affected device. A successful exploit is read-only: the attacker can view arbitrary files within the web services file system, potentially leaking sensitive device or configuration content, but cannot modify the device or take full control. Any organization running ASA or FTD software with the web services interface reachable — commonly an internet-facing VPN or web portal — is affected. The flaw is listed in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) with a reported ~100% EPSS probability of exploitation, indicating it is being actively exploited in the wild; ransomware use is unknown.

Do: Apply Cisco's fixed software releases for ASA and FTD as directed in the vendor advisory. Until patched, restrict access to the device's web services/WebVPN interface to trusted source addresses or disable web services if not in use. Review device HTTP logs for crafted requests containing directory traversal sequences against the web portal, which would indicate exploitation attempts.

A vulnerability in the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a denial of service (DoS) condition. This vulnerability is due to improper input validation when parsing HTTPS requests. An attacker could exploit this vulnerability by sending a malicious HTTPS request to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.