CVE-2025-20246: Cisco Webex Meetings XSS Vulnerability

CVE-2025-20246 Overview

Cisco disclosed CVE-2025-20246, a reflected cross-site scripting (XSS) vulnerability affecting Cisco Webex Meetings. The flaw stems from improper filtering of user-supplied input in the web interface. An unauthenticated, remote attacker can exploit the issue by persuading a user to follow a crafted link. Successful exploitation executes arbitrary script code in the context of the targeted user's browser session, potentially exposing session data or enabling further client-side attacks. The vulnerability is classified under [CWE-79] (Improper Neutralization of Input During Web Page Generation). Cisco has published advisory cisco-sa-webex-xss-7teQtFn8 addressing the issue.

Critical Impact
Attackers can execute arbitrary script in a victim's browser session against Cisco Webex Meetings, enabling session data theft, credential harvesting, and content spoofing through a single malicious link click.

Affected Products

Cisco Webex Meetings
Cisco Webex Meetings web interface (all versions prior to the fixed release referenced in Cisco advisory cisco-sa-webex-xss-7teQtFn8)
Deployments exposing the affected Webex Meetings endpoints to untrusted users

Discovery Timeline

2025-05-21 - CVE-2025-20246 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-20246

Vulnerability Analysis

CVE-2025-20246 is a reflected cross-site scripting (XSS) flaw in Cisco Webex Meetings. The application accepts user-controlled input through a request parameter and reflects it back into the rendered HTML response without sufficient output encoding or input sanitization. When a victim loads a crafted URL, the injected payload executes within the origin of the Webex Meetings site.

Because the attack requires only that a user click a malicious link, adversaries typically deliver these URLs through phishing, chat platforms, or embedded links in meeting invitations. The scope is marked as changed, meaning the injected script can affect resources beyond the initially vulnerable component, such as parent frames or federated authentication flows.

The attacker does not need credentials or existing access to the Webex tenant. However, the payload executes with the privileges of whichever user follows the link, which may include authenticated meeting hosts, administrators, or attendees.

Root Cause

The root cause is improper neutralization of user-supplied input before it is placed in HTML output. The Webex Meetings component fails to apply context-appropriate encoding (HTML entity, attribute, or JavaScript escaping) to parameter values reflected in server responses. This aligns with the [CWE-79] classification recorded in the NVD entry.

Attack Vector

Exploitation proceeds through the following sequence:

The attacker crafts a URL to a vulnerable Cisco Webex Meetings endpoint containing a JavaScript payload in a reflected parameter.
The attacker delivers the URL via phishing email, instant message, or malicious meeting invitation.
The victim clicks the link while authenticated to Webex or on the Webex origin.
The server returns a response embedding the unsanitized payload, and the victim's browser executes it in the Webex origin context.
The payload can read session tokens, forge requests to Webex APIs, capture keystrokes, or redirect the user to attacker-controlled resources.

No verified public proof-of-concept has been published. Refer to the Cisco Security Advisory for vendor-supplied technical details.

Detection Methods for CVE-2025-20246

Indicators of Compromise

Inbound URLs to Webex Meetings endpoints containing script tags, javascript: schemes, event handlers such as onerror= or onload=, or URL-encoded equivalents in query parameters.
Web proxy or email gateway logs showing users clicking Webex links originating from external senders with unusually long or obfuscated query strings.
Browser telemetry showing unexpected script execution or DOM modifications on Webex Meetings origins.

Detection Strategies

Inspect HTTP request logs from web proxies and CASB solutions for Webex Meetings URLs containing XSS payload signatures such as <script, %3Cscript, onerror=, or document.cookie.
Correlate email gateway URL rewriting telemetry with click-through events to identify users who followed suspicious Webex links.
Apply signature-based Web Application Firewall (WAF) rules on reverse-proxied Webex traffic to flag reflected payloads in request parameters.

Monitoring Recommendations

Enable Content Security Policy (CSP) violation reporting for Webex domains to surface unexpected inline script execution.
Monitor endpoint browser processes for anomalous child processes or credential-access behavior following visits to Webex URLs.
Track authentication anomalies against Webex accounts, including new session tokens issued shortly after users click external links.

How to Mitigate CVE-2025-20246

Immediate Actions Required

Apply the fixed Cisco Webex Meetings release referenced in advisory cisco-sa-webex-xss-7teQtFn8 as soon as it is available in your tenant.
Notify Webex users to avoid clicking Webex Meetings links received from untrusted or unsolicited sources until patching is confirmed.
Enable URL rewriting and safe-link inspection in email security gateways to detonate suspicious Webex links before delivery.

Patch Information

Cisco has published security advisory cisco-sa-webex-xss-7teQtFn8 with remediation guidance. Refer to the Cisco Security Advisory for fixed version details and cloud-side remediation status. Cisco Webex Meetings is a hosted service, and cloud-tenant fixes are typically applied by Cisco without customer action; verify tenant version through the Webex Control Hub.

Workarounds

Restrict access to Webex Meetings web endpoints from unmanaged networks where feasible using conditional access or SSO policies.
Configure browser-side protections such as strict Content Security Policy enforcement and same-site cookie attributes for Webex sessions.
Deliver targeted user awareness training focused on identifying spoofed Webex meeting invitations and shortened URLs.

bash

# Example: WAF rule snippet to block reflected XSS payloads on Webex URLs
SecRule REQUEST_URI "@rx (?i)webex" \
  "chain,phase:2,deny,status:403,id:1002025,msg:'Potential XSS targeting Cisco Webex (CVE-2025-20246)'"
  SecRule ARGS "@rx (?i)(<script|javascript:|onerror=|onload=|%3Cscript)" \
    "t:none,t:urlDecodeUni"