CVE-2017-3807 Cisco CVE debrief

Who should care

Cisco ASA administrators and security teams operating ASA 9.0-9.6 deployments with Clientless SSL VPN enabled, especially systems in routed firewall mode and single- or multiple-context mode. Organizations that allow portal logins over TCP from untrusted networks should treat this as priority exposure.

Technical summary

The vulnerability is categorized as CWE-119 and carries CVSS 3.0 8.8/High (AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H). According to the supplied corpus, the issue exists in Common Internet Filesystem (CIFS) handling within Clientless SSL VPN on Cisco ASA Software major releases 9.0-9.6. Exploitation requires valid portal credentials and a valid TCP connection, and Cisco notes that only traffic directed to the affected system can be used. The flaw can be triggered by IPv4 or IPv6 traffic and affects routed firewall mode deployments only.

Defensive priority

High — prioritize patching or mitigating any ASA instance that exposes Clientless SSL VPN in the affected mode, because the flaw is remotely reachable by authenticated users and can affect availability and possibly confidentiality/integrity.

Recommended defensive actions

• Review Cisco’s vendor advisory referenced in NVD for fixed releases and apply the recommended software update path as soon as possible.
• Identify ASA devices running Clientless SSL VPN in routed firewall mode and confirm whether they fall within the affected Cisco ASA release families listed in the NVD record.
• Restrict portal access to only necessary users and trusted source networks, and remove or disable Clientless SSL VPN where it is not required.
• Monitor ASA authentication and VPN-portal activity for unusual logins, crafted request patterns, or unexpected reloads.
• Keep network and host defenses tuned to detect and alert on directed traffic to the portal, including both IPv4 and IPv6 paths.
• If immediate patching is not possible, use compensating controls to reduce exposure and document the remaining risk until remediation is complete.

Evidence notes

This debrief is based on the supplied NVD CVE record for CVE-2017-3807 and the Cisco advisory reference cited by NVD. The corpus describes a heap overflow in CIFS code within Clientless SSL VPN, caused by insufficient input validation, exploitable by an authenticated remote attacker using a crafted URL. The record also states the attack requires valid credentials, a valid TCP connection, directed traffic to the affected system, and that impacted deployments are routed firewall mode only. NVD assigns CWE-119 and CVSS:3.0/8.8.

Official resources