Cisco Jabber Bug Could Let Hackers Target Windows Systems Remotely

Networking equipment maker Cisco has released a new version of its Jabber video conferencing and messaging app for Windows that includes patches for multiple vulnerabilities—which, if exploited, could allow an authenticated, remote attacker to execute arbitrary code.

The flaws, which were uncovered by Norwegian cybersecurity firm Watchcom during a pentest, affect all currently supported versions of the Jabber client (12.1-12.9) and has since been fixed by the company.

Two of the four flaws can be exploited to gain remote code execution (RCE) on target systems by sending specially crafted chat messages in group conversations or specific individuals.

The most severe of the lot is a flaw (CVE-2020-3495, CVSS score 9.9) that's caused by improper validation of message contents, which could be leveraged by an attacker by sending maliciously-crafted Extensible Messaging and Presence Protocol (XMPP) messages to the affected software.

"A successful exploit could allow the attacker to cause the application to execute arbitrary programs on the targeted system with the privileges of the user account that is running the Cisco Jabber client software, possibly resulting in arbitrary code execution," Cisco said in an advisory published yesterday.

The development comes days after Cisco warned of an actively exploited zero-day flaw in its IOS XR router software.

An XSS Flaw to an RCE Flaw

XMPP (originally called Jabber) is an XML-based communications protocol used for facilitating instant messaging between any two or more network entities.

It's also designed to be extensible so as to accommodate additional functionality, one of which is XEP-0071: XHTML-IM — a specification that lays down the rules for exchanging HTML content using the XMPP protocol.

The flaw in Cisco Jabber arises from cross-site scripting (XSS) vulnerability when parsing XHTML-IM messages.

"The application does not properly sanitize incoming HTML messages and instead passes them through a flawed XSS filter," Watchcom researchers explained.

As a consequence, a legitimate XMPP message can be intercepted and modified, thereby causing the application to run an arbitrary executable that already exists within the local file path of the application.

To achieve this, it takes advantage of a separate vulnerable function in Chromium Embedded Framework (CEF) — an open-source framework that's used to embed a Chromium web browser within other apps — that could be abused by a bad actor to execute rogue ".exe" files on the victim's machine.

Attackers, however, are required to have access to their victims' XMPP domains to send the malicious XMPP messages needed to exploit the vulnerability successfully.

Additionally, three other flaws in Jabber (CVE-2020-3430, CVE-2020-3498, CVE-2020-3537) could be exploited to inject malicious commands and cause information disclosure, including the possibility of stealthily collecting users' NTLM password hashes.

With video conferencing applications becoming popular in the wake of the pandemic, it's essential that Jabber users update to the latest version of the software to mitigate the risk.

"Given their newfound prevalence in organizations of all sizes, these applications are becoming an increasingly attractive target for attackers," Watchcom said. "A lot of sensitive information is shared through video calls or instant messages and the applications are used by the majority of employees, including those with privileged access to other IT systems."

"The security of these applications is therefore paramount, and it is important to ensure that both the applications themselves, and the infrastructure they are using, are regularly audited for security gaps."