CVE-2021-1221 in WebEx Meetings
Summary
by MITRE • 02/05/2021
A vulnerability in the user interface of Cisco Webex Meetings and Cisco Webex Meetings Server Software could allow an authenticated, remote attacker to inject a hyperlink into a meeting invitation email. The vulnerability is due to insufficient input validation. An attacker could exploit this vulnerability by entering a URL into a field in the user interface. A successful exploit could allow the attacker to generate a Webex Meetings invitation email that contains a link to a destination of their choosing. Because this email is sent from a trusted source, the recipient may be more likely to click the link.
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Analysis
by VulDB Data Team • 02/24/2021
This vulnerability resides within the user interface of Cisco Webex Meetings and Cisco Webex Meetings Server Software, representing a critical security flaw that enables authenticated remote attackers to manipulate meeting invitation emails through malicious hyperlink injection. The vulnerability stems from inadequate input validation mechanisms within the software's interface, specifically in fields designed to accept URL inputs for meeting invitations. According to CWE-20, this represents a classic input validation weakness where the system fails to properly sanitize or validate user-supplied data before incorporating it into generated content. The flaw allows attackers with legitimate authentication credentials to craft malicious meeting invitations that contain deceptive hyperlinks pointing to attacker-controlled destinations.
The operational impact of this vulnerability extends beyond simple phishing attempts, as it leverages the trusted sender reputation inherent to the Webex platform to increase social engineering effectiveness. When authenticated users create meeting invitations, the system processes their input without sufficient validation, permitting the injection of malicious URLs that appear to originate from legitimate Webex sources. This creates a sophisticated attack vector where recipients are more likely to trust and interact with the malicious links due to the perceived authenticity of the email source. The vulnerability specifically affects the email generation process within the Webex ecosystem, making it particularly dangerous for organizations that rely heavily on Webex for business communications and collaboration.
Attackers can exploit this weakness by simply entering a crafted URL into the appropriate field within the Webex user interface, bypassing traditional security controls that would normally prevent such malicious input. The system's insufficient validation allows arbitrary URLs to be embedded directly into the generated meeting invitation emails, which are then distributed to meeting participants. This vulnerability aligns with ATT&CK technique T1566, specifically the "Phishing" sub-technique, where attackers leverage trusted email sources to increase the success rate of their social engineering campaigns. The attack chain typically involves authentication, input manipulation, email generation, and delivery to unsuspecting recipients who may inadvertently execute malicious payloads or reveal sensitive information upon clicking the compromised links.
Organizations should implement immediate mitigations including enhanced input validation controls, regular security assessments of the Webex platform, and employee training on recognizing suspicious email content. Cisco has released patches addressing this vulnerability, and administrators should prioritize applying these updates to prevent exploitation. Additional defensive measures include monitoring for unusual email content patterns, implementing email filtering solutions that can detect suspicious URL structures, and establishing clear protocols for verifying meeting invitation authenticity. The vulnerability demonstrates the importance of validating all user inputs and the critical need for security controls that prevent authenticated users from injecting malicious content into trusted communication channels, as outlined in the OWASP Top Ten security principles.