CVE-2025-20235 Overview
CVE-2025-20235 is a reflected cross-site scripting (XSS) vulnerability in the web-based management interface of Cisco Secure Firewall Management Center (FMC) Software. The flaw stems from insufficient validation of user-supplied input in various data fields exposed by the interface. An unauthenticated, remote attacker can craft malicious input that, when rendered by a targeted administrator's browser, executes arbitrary script in the context of the FMC interface. Successful exploitation can lead to browser-based information disclosure or unauthorized actions performed in the victim's session. The weakness is classified as [CWE-79] Improper Neutralization of Input During Web Page Generation.
Critical Impact
An unauthenticated remote attacker can execute arbitrary script in an administrator's browser session on the Cisco FMC web interface, exposing sensitive session data and enabling actions on behalf of the victim.
Affected Products
- Cisco Secure Firewall Management Center Software 6.2.3 through 6.2.3.18
- Cisco Secure Firewall Management Center Software 6.4.0 through 7.4.2.2
- Cisco Secure Firewall Management Center Software 7.6.0
Discovery Timeline
- 2025-08-14 - CVE-2025-20235 published to the National Vulnerability Database
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-20235
Vulnerability Analysis
The vulnerability resides in the web-based management interface used by administrators to configure Cisco Secure Firewall deployments. Input fields accepting user-supplied data are not adequately sanitized or encoded before being reflected back into rendered HTML responses. When an authenticated user visits a crafted URL or interacts with attacker-influenced data, injected JavaScript executes within the trusted origin of the FMC interface.
Because the interface manages firewall policy, script execution in an administrator context can be leveraged to read session tokens, exfiltrate policy data visible in the DOM, or issue configuration requests through the victim's authenticated session. User interaction is required, so exploitation typically involves phishing or social engineering to lure an authenticated administrator into triggering the payload.
Root Cause
The root cause is missing output encoding and insufficient input validation on multiple data fields processed by the FMC web interface. User-controlled input flows into HTML response contexts without contextual escaping, allowing HTML and script tokens to be interpreted by the browser rather than displayed as literal text.
Attack Vector
The attack is delivered over the network. An unauthenticated attacker crafts a URL or payload containing malicious script and delivers it to a valid FMC user, typically through phishing. When the user clicks the link or loads the crafted content while authenticated to the FMC interface, the browser executes the attacker's script in the interface's origin, exposing session information and interface functionality to the attacker.
No verified exploit code has been published for CVE-2025-20235. Refer to the Cisco Security Advisory for authoritative technical details.
Detection Methods for CVE-2025-20235
Indicators of Compromise
- Unexpected HTTP GET or POST requests to FMC web interface endpoints containing HTML tags, <script>, javascript:, or URL-encoded script fragments in query parameters or form fields.
- Referer headers pointing to external, unfamiliar domains preceding administrator sessions on the FMC.
- Browser console errors or unusual outbound requests originating from an administrator workstation while an FMC session is active.
Detection Strategies
- Inspect FMC web server logs for requests containing suspicious payloads such as %3Cscript%3E, onerror=, onload=, or other event-handler patterns in parameter values.
- Deploy web application firewall (WAF) rules in front of the FMC management interface to flag reflected XSS signatures in requests and responses.
- Correlate administrator browser sessions with anomalous configuration change events on the FMC to identify session abuse following a suspected XSS payload.
Monitoring Recommendations
- Restrict access to the FMC management interface to a dedicated management network and monitor all inbound connections to that segment.
- Log and review administrator activity in the FMC audit trail, focusing on configuration changes that occur shortly after external link clicks.
- Monitor email and messaging gateways for links referencing internal FMC hostnames or IPs that could be used to deliver crafted XSS payloads.
How to Mitigate CVE-2025-20235
Immediate Actions Required
- Apply the fixed software releases identified in the Cisco Security Advisory cisco-sa-fmc-xss-JtNmcusP.
- Limit access to the FMC web-based management interface to trusted management networks and named administrator workstations.
- Instruct administrators to avoid clicking untrusted links while authenticated to the FMC and to use a dedicated browser profile for firewall management.
Patch Information
Cisco has released free software updates that address CVE-2025-20235 for supported FMC releases. Refer to the Cisco Security Advisory for the specific fixed release matching your currently deployed FMC version, and follow standard Cisco upgrade procedures to install the patched release.
Workarounds
- No workarounds are listed by Cisco for this vulnerability; upgrading to a fixed release is required.
- As a compensating control, isolate the FMC management interface behind a jump host or VPN and enforce short session timeouts for administrators.
- Enforce browser-based protections such as strict content security policies at the network egress layer and disallow administrative browsing to external sites from FMC management workstations.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
