Comodo Leaves AV Vulnerabilities Unpatched

Multiple zero-day vulnerabilities were found in version 12.0.0.6810 of Comodo Antivirus by security firm Tenable. Even though Comodo was notified by Tenable in April of the problems, no patches have been forthcoming from the antivirus firm.

The most pressing of them is CVE-2019-3969, which allows an attacker with access to the targeted system to escape the Comodo Antivirus sandbox (which Comodo refers to as "containment") and escalate privileges to SYSTEM. It has a CVSS score of 6.8 (classified as "medium" or "low" severity) because the vulnerabilities need access to the target system in order to affect it.

David Wells, the researcher who found the problems, described them in much detail in a blog that he wrote on Medium.

But Tenable summarizes the problem this way: "An attacker can bypass this signing check (done for validity—ed.) however by changing the client's process name within its PEB (Process Environment Block), or process hollowing a Comodo/Microsoft signed processes with malicious code. This is because CmdAgent's signature check uses the filename from EnumProcessModules / GetModuleFilename for the COM Client's PID. Once passing trusted binary check, an attacker can obtain an Instance of IServiceProvider. With IServiceProvider, the attacker can then query for an interface to SvcRegKey and perform registry writes through the Out-Of-Proc COM server as "NT AUTHORTIY\SYSTEM", allowing local privilege escalation."

That explanation is composed of fairly dense verbiage, but the problem involves loopbacks within the program structures at a fairly low level.

It has been reported that Comodo says the privilege escalation vulnerability was partly Microsoft's fault, and they may well be looking at the possibility that a PEB name change can occur as a primary cause.

Other problems that Tenable discovered include CVE-2019-3970, an arbitrary file write issue which may allow an attacker to modify virus definitions within the AV. With it, the attacker can create false positives (arbitrary file quarantine) or even allow some malware to bypass signature-based detection.

Three more vulnerabilities reported by Tenable include CVE-2019-3972 (an out-of-bounds read that involves CmdAgent.exe), CVE-2019-3973 (an out-of-bounds write affecting Cmdguard.sys), and 9-3971 (denial of service involving CmdVirth.exe).

CVE-2019-3973 only affects versions of the Comodo AV up to 11.0.0.6582.

The last three CVEs can cause individual application components as well as the kernel to crash.

Wells has posted a proof-of-concept (PoC) exploit code along with a video that shows the exploit in action.

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.