CVE-2025-20148: Cisco Secure Firewall Center XSS Flaw

CVE-2025-20148 Overview

Cisco disclosed CVE-2025-20148, an HTML injection vulnerability in the web-based management interface of Cisco Secure Firewall Management Center (FMC) Software. An authenticated, remote attacker can inject arbitrary HTML content into a device-generated document. Exploitation requires valid credentials for a user account with at least the Security Analyst (Read Only) role.

The flaw stems from improper validation of user-supplied data [CWE-20]. A successful exploit allows attackers to alter document layouts, read arbitrary files from the underlying operating system, and conduct server-side request forgery (SSRF) attacks against internal resources.

Critical Impact
Authenticated attackers with low-privilege accounts can read arbitrary files from the FMC operating system and pivot to internal services via SSRF, exposing sensitive configuration data and management infrastructure.

Affected Products

Cisco Secure Firewall Management Center 7.0.6 through 7.0.6.3
Cisco Secure Firewall Management Center 7.2.4 through 7.2.9
Cisco Secure Firewall Management Center 7.4.0 through 7.4.2.1

Discovery Timeline

2025-08-14 - CVE-2025-20148 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-20148

Vulnerability Analysis

The vulnerability resides in the document-generation feature of the FMC web-based management interface. Cisco FMC allows administrators and analysts to generate reports and exports describing device configuration, policy state, and operational data. The reporting subsystem accepts user-supplied input but fails to sanitize HTML markup before embedding it into rendered documents.

An attacker submits crafted HTML or markup containing references to local files or external URLs. When the FMC renders the document, the server processes those references in its own context. This converts what should be a benign reporting feature into a primitive for reading files on the underlying operating system and issuing outbound HTTP requests from the FMC host.

The attacker only needs the Security Analyst (Read Only) role, which is commonly granted to monitoring staff and downstream operations teams. This lowers the practical bar for exploitation in environments with broad analyst access.

Root Cause

The root cause is improper input validation [CWE-20] in the document-rendering path. User-controlled fields are passed to the rendering engine without HTML escaping or allowlist filtering. The engine then interprets injected markup, including markup that triggers file inclusion or outbound requests.

Attack Vector

The attack vector is network-based through the FMC web management interface. The attacker authenticates with valid credentials, submits malicious content to a field consumed by the reporting subsystem, and triggers document generation. The rendered document contains the attacker's injected payload along with any file contents or SSRF response data fetched by the server during rendering.

No verified public proof-of-concept code is available. Refer to the Cisco Security Advisory cisco-sa-fmc-html-inj-MqjrZrny for vendor technical details.

Detection Methods for CVE-2025-20148

Indicators of Compromise

Unexpected document or report generation requests from Security Analyst (Read Only) accounts in FMC audit logs.
Outbound HTTP/HTTPS connections originating from the FMC management host to internal or external addresses outside its normal update and licensing endpoints.
Generated reports containing unexpected HTML tags, file:// references, or external URL fetches.
Anomalous file access patterns on the FMC operating system targeting /etc/, configuration directories, or credential stores.

Detection Strategies

Audit FMC audit.log for report and document generation actions correlated with low-privilege accounts.
Inspect generated documents for embedded HTML markup, external resource references, or content that does not match expected report templates.
Monitor egress from FMC management interfaces for connections to non-standard destinations or internal network ranges not previously contacted.

Monitoring Recommendations

Forward FMC audit logs and syslog data to a centralized SIEM and alert on report generation by accounts that historically do not produce reports.
Baseline normal outbound traffic from FMC appliances and alert on deviations, particularly RFC1918 destinations and metadata service endpoints.
Review user role assignments and flag any account with Security Analyst (Read Only) access that begins generating documents at unusual frequency.

How to Mitigate CVE-2025-20148

Immediate Actions Required

Upgrade Cisco Secure Firewall Management Center to a fixed release as identified in the Cisco Security Advisory.
Restrict FMC web management interface access to trusted management networks using network ACLs or jump hosts.
Audit and reduce the number of accounts holding Security Analyst (Read Only) or higher privileges to the minimum required.
Rotate credentials for any FMC account suspected of misuse or shared across multiple users.

Patch Information

Cisco has released fixed software addressing CVE-2025-20148. Administrators should consult the Cisco Security Advisory cisco-sa-fmc-html-inj-MqjrZrny for the specific fixed releases corresponding to the 7.0, 7.2, and 7.4 trains and apply the upgrade through standard Cisco upgrade procedures.

Workarounds

No vendor-provided workarounds are listed in the Cisco advisory; upgrading to a fixed release is the supported remediation.
As a compensating control, limit access to the FMC web management interface to a small set of administrative source IPs.
Enforce strict role-based access control and remove unnecessary Security Analyst accounts until patching is complete.
Monitor FMC audit logs closely for report generation activity until upgrades are deployed.

bash

# Example: restrict FMC management access via upstream firewall ACL
# Replace <FMC_MGMT_IP> and <ADMIN_SUBNET> with environment values
access-list FMC_MGMT permit tcp <ADMIN_SUBNET> host <FMC_MGMT_IP> eq 443
access-list FMC_MGMT deny   tcp any host <FMC_MGMT_IP> eq 443
access-list FMC_MGMT permit ip any any