CVE-2026-20123: Cisco EPNM XSS Vulnerability Explained

CVE-2026-20123 Overview

A vulnerability in the web-based management interface of Cisco Evolved Programmable Network Manager (EPNM) and Cisco Prime Infrastructure could allow an unauthenticated, remote attacker to redirect a user to a malicious web page. This vulnerability is classified as an Open Redirect (CWE-601) and stems from improper input validation of parameters in HTTP requests.

An attacker could exploit this vulnerability by intercepting and modifying an HTTP request from a user. A successful exploit could allow the attacker to redirect the user to a malicious web page, potentially facilitating phishing attacks, credential theft, or malware delivery.

Critical Impact

Unauthenticated attackers can redirect authenticated users to malicious websites by manipulating HTTP request parameters, enabling phishing and credential harvesting attacks against network administrators.

Affected Products

• Cisco Evolved Programmable Network Manager (EPNM)
• Cisco Prime Infrastructure
• Web-based management interface components

Discovery Timeline

• February 4, 2026 - CVE-2026-20123 published to NVD
• February 5, 2026 - Last updated in NVD database

Technical Details for CVE-2026-20123

Vulnerability Analysis

This Open Redirect vulnerability (CWE-601) affects the web-based management interface of Cisco Evolved Programmable Network Manager (EPNM) and Cisco Prime Infrastructure. The vulnerability allows unauthenticated remote attackers to redirect users to arbitrary external URLs by manipulating HTTP request parameters.

Open redirect vulnerabilities occur when an application accepts user-controlled input that specifies a URL for redirection without proper validation. In this case, the web management interface fails to adequately sanitize URL parameters before performing redirects, allowing attackers to craft malicious links that appear to originate from a trusted Cisco management domain.

The attack requires user interaction—specifically, a victim must click on a crafted link or have their HTTP request intercepted and modified. While this limits automated exploitation, the trust users place in their network management infrastructure makes this an effective vector for targeted phishing campaigns against network administrators.

Root Cause

The root cause of this vulnerability is improper input validation of the parameters in HTTP requests processed by the web-based management interface. The application fails to verify that redirect URLs point to legitimate, trusted destinations before performing the redirection, allowing arbitrary external URLs to be specified by attackers.

Attack Vector

The attack vector is network-based and does not require authentication. An attacker could exploit this vulnerability through several methods:

1. Crafted Malicious Links: Creating URLs that point to the legitimate Cisco management interface but contain parameters redirecting users to attacker-controlled sites
2. Man-in-the-Middle Interception: Intercepting and modifying legitimate HTTP requests to inject malicious redirect parameters
3. Phishing Campaigns: Distributing crafted links via email or other channels that leverage the trusted Cisco domain to redirect victims to credential harvesting pages

The attack mechanism involves manipulating URL parameters to specify an attacker-controlled destination. When users click these links expecting to access their network management interface, they are instead redirected to a malicious site that may impersonate the login page or deliver malware.

Detection Methods for CVE-2026-20123

Indicators of Compromise

• HTTP requests to EPNM or Prime Infrastructure containing unexpected URL parameters with external domain references
• User complaints of being redirected to unfamiliar websites when accessing management interfaces
• Authentication failures following legitimate-looking login attempts that were actually directed to phishing sites
• Anomalous outbound connections from systems that recently accessed the management interface

Detection Strategies

• Monitor HTTP request logs for the web management interface, focusing on requests containing redirect parameters pointing to external domains
• Implement URL parameter analysis to detect requests with suspicious external URL values
• Deploy network security monitoring to identify unusual redirect patterns or connections to known malicious domains
• Review web server access logs for patterns indicating crafted URL exploitation attempts

Monitoring Recommendations

• Enable detailed logging on Cisco EPNM and Prime Infrastructure web interfaces
• Configure SIEM rules to alert on HTTP requests containing external URLs in redirect parameters
• Monitor for phishing indicators targeting network administrator credentials
• Track user-agent and referrer headers for anomalous patterns indicating link manipulation

How to Mitigate CVE-2026-20123

Immediate Actions Required

• Review the Cisco Security Advisory for official guidance and patch availability
• Educate network administrators about the risks of clicking links to management interfaces from untrusted sources
• Implement network segmentation to limit access to management interfaces to trusted networks only
• Consider deploying a web application firewall (WAF) to filter requests with suspicious redirect parameters

Patch Information

Cisco has released a security advisory addressing this vulnerability. Organizations should consult the Cisco Security Advisory cisco-sa-epnm-pi-redirect-6sX82dN for specific patch versions and upgrade instructions for both Cisco Evolved Programmable Network Manager and Cisco Prime Infrastructure.

Workarounds

• Restrict access to the web-based management interface to trusted IP addresses and networks using ACLs or firewall rules
• Require VPN connectivity before accessing management interfaces to reduce exposure
• Implement browser security policies that warn users when navigating away from trusted domains
• Train users to verify URLs manually before entering credentials, especially when redirected from management interface links

# Example ACL configuration to restrict management interface access
# Apply to the interface serving EPNM/Prime Infrastructure
access-list 100 permit tcp 10.0.0.0 0.255.255.255 host 192.168.1.100 eq 443
access-list 100 deny tcp any host 192.168.1.100 eq 443
access-list 100 permit ip any any