CVE-2017-3827 Cisco CVE debrief

Who should care

Administrators of Cisco ESA and WSA deployments that use message filters, content filters, attachment scanning, or web-content scanning should pay attention, especially where those controls are relied on to block or route risky content.

Technical summary

The vulnerability is in the Multipurpose Internet Mail Extensions (MIME) scanner used by Cisco AsyncOS. According to the source description, the flaw can allow an unauthenticated remote attacker to bypass configured user filters on the appliance. The affected scope includes Cisco ESA and Cisco WSA appliances, virtual and hardware, when configured to scan incoming email attachments on ESA or scan web access content on WSA. NVD lists the weakness as CWE-20 and the attack vector as network-based, with no privileges or user interaction required and a confidentiality impact of none plus a low integrity impact.

Defensive priority

Medium priority. The issue does not indicate code execution or full device compromise in the supplied corpus, but it can defeat security policy controls that administrators may rely on for filtering malicious or unwanted content.

Recommended defensive actions

• Review whether any Cisco ESA or WSA appliances in your environment are running affected AsyncOS releases listed by Cisco/NVD.
• Upgrade to the first fixed release for your platform as indicated in Cisco's advisory before relying on filtering controls for enforcement.
• Validate message and content filter behavior after patching, especially workflows that scan email attachments or web-access content.
• Treat filter bypass as a policy-enforcement issue and reassess compensating controls such as layered gateway scanning, endpoint detection, and content inspection logging.
• Monitor Cisco advisory and NVD references for any platform-specific remediation guidance or release confirmations.

Evidence notes

Source corpus states that the issue affects Cisco AsyncOS Software for Cisco ESA and WSA and can let an unauthenticated remote attacker bypass configured user filters. NVD metadata classifies the weakness as CWE-20 and provides CVSS 3.0 vector CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N, supporting network-based exploitation with integrity impact. Cisco advisory reference is included in the NVD record.

Official resources