A new elevation of privilege vulnerability has been discovered in the Cisco WebEx Meetings desktop app for Windows® by security researcher Marcos Accossatto from SecureAuth Exploits’ Writers Team.
This vulnerability, tracked as CVE-2019-1674, is an OS Command Injection that can be used to bypass new controls that Cisco put in place after patching a previously disclosed DLL hijacking issue in 2018. This vulnerability could allow a local attacker to elevate their privileges by invoking the update service command. An attacker could exploit this flaw by swapping out the Cisco WebEx Meetings update binary with “a previous vulnerable version through a fake update… that will load a malicious DLL.” The researchers also noted that while this vulnerability can only be exploited locally, it could be exploited remotely in an Active Directory setup through operating system remote management tools.
The update service for Cisco WebEx Meetings uses XML to check against new files when installing an update. However, this vulnerability would fail to validate version numbers of new files. This is how attackers could potentially insert different files into the update service and trick the update service into “updating” the program to an older, insecure version of Cisco WebEx Meetings. According to SecureAuth, “The vulnerability can be exploited by copying to a local attacker controller folder, the ptUpdate.exe binary. Also, a malicious dll must be placed in the same folder, named wbxtrace.dll. To gain privileges, the attacker must start the service with the command line: sc start webexservice install software-update 1 ‘attacker-controlled-path’ (if the parameter 1 doesn't work, then 2 should be used).” The research team also released a two-step Proof of Concept showing how this vulnerability can be exploited.
The timeline for this vulnerability is about 2 months long and is as follows: on Dec. 4, 2018, SecureAuth sent the initial notification to Cisco PSIRT. On Dec. 5, 2018, Cisco confirmed they received the advisory and opened a case for it, and on Dec. 7, 2018, Cisco confirmed that they were able to reproduce the vulnerability and began working on a plan to fix it. On Dec. 10, 2018, Cisco told SecureAuth that the fix for the vulnerability would be generally available by the end of February. After a couple of attempts by SecureAuth to get updates on the status of the patch for the vulnerability, Cisco, on Jan. 22, 2019, said they were still aiming for an end of February release. Finally, on Feb. 11, 2019, Cisco confirmed that Feb. 27, 2019 would be the official disclosure date, and have now disclosed a patch for this security vulnerability.
If your company uses Cisco WebEx Meetings desktop app on Windows, be sure to update it immediately to avoid any potential attacks due to this vulnerability.