CVE-2026-20155: Cisco EPNM Information Disclosure Flaw

CVE-2026-20155 Overview

A vulnerability in the web-based management interface of Cisco Evolved Programmable Network Manager (EPNM) allows an authenticated, remote attacker with low privileges to access sensitive information that they are not authorized to access. This improper authorization vulnerability (CWE-862) exists due to inadequate authorization checks on a REST API endpoint of an affected device.

An attacker could exploit this vulnerability by querying the affected endpoint. A successful exploit could allow the attacker to view session information of active Cisco EPNM users, including users with administrative privileges, which could result in the affected device being compromised.

Critical Impact

Low-privileged authenticated attackers can access administrative session information via REST API, potentially leading to full system compromise through session hijacking.

Affected Products

• Cisco Evolved Programmable Network Manager (EPNM) - Web-based Management Interface
• Cisco EPNM REST API Endpoints

Discovery Timeline

• April 1, 2026 - CVE-2026-20155 published to NVD
• April 1, 2026 - Last updated in NVD database

Technical Details for CVE-2026-20155

Vulnerability Analysis

This vulnerability falls under the category of Missing Authorization (CWE-862), where the affected REST API endpoint fails to properly verify that the requesting user has adequate privileges to access the requested information. The flaw exists in the web-based management interface of Cisco EPNM, which is used for managing and monitoring network infrastructure.

The vulnerability is particularly concerning because it allows attackers with minimal privileges to escalate their access by harvesting session tokens from higher-privileged users. Once an attacker obtains administrative session information, they could potentially hijack those sessions and gain full control over the network management system.

Root Cause

The root cause of this vulnerability is improper authorization checks on a REST API endpoint within the Cisco EPNM web-based management interface. The application fails to verify that authenticated users requesting session information have the appropriate privilege level to view such sensitive data. This authorization bypass allows any authenticated user, regardless of their assigned role, to query and retrieve session details for all active users including administrators.

Attack Vector

The attack is network-based and requires the attacker to have valid credentials for the Cisco EPNM system, even with low-privilege access. The exploitation flow involves:

1. An attacker authenticates to the Cisco EPNM web interface using low-privilege credentials
2. The attacker identifies and queries the vulnerable REST API endpoint
3. The endpoint returns session information for all active users, including administrative accounts
4. The attacker can use the exposed session tokens to hijack privileged sessions
5. With hijacked administrative sessions, the attacker gains full control of the EPNM system

The vulnerability requires user interaction as indicated by the attack vector characteristics, suggesting that certain conditions or user actions may be necessary for successful exploitation.

Detection Methods for CVE-2026-20155

Indicators of Compromise

• Unusual REST API queries from low-privileged user accounts targeting session-related endpoints
• Multiple session information requests originating from the same low-privileged user
• Administrative session access from unexpected IP addresses or user agents following API queries
• Audit log entries showing low-privileged users accessing privileged session data

Detection Strategies

• Monitor REST API access logs for unusual patterns of session endpoint queries from low-privileged accounts
• Implement anomaly detection for users accessing resources outside their normal permission scope
• Alert on multiple authentication sessions originating from the same credentials with different session tokens
• Review access control logs for any signs of privilege escalation attempts

Monitoring Recommendations

• Enable detailed logging on all REST API endpoints in Cisco EPNM
• Configure SIEM alerts for session enumeration patterns and unauthorized data access attempts
• Implement user behavior analytics to detect abnormal access patterns from low-privileged accounts
• Monitor network traffic for unusual volumes of API requests targeting the management interface

How to Mitigate CVE-2026-20155

Immediate Actions Required

• Review the Cisco Security Advisory for specific patch availability and instructions
• Audit all low-privileged user accounts for unnecessary access and suspicious activity
• Implement network segmentation to restrict access to the EPNM management interface
• Review and terminate any suspicious active sessions in the EPNM system

Patch Information

Cisco has published a security advisory for this vulnerability. Organizations should consult the Cisco Security Advisory cisco-sa-epnm-improp-auth-mUwFWUU3 for detailed patch information, fixed software versions, and upgrade instructions specific to their deployment.

Workarounds

• Restrict network access to the Cisco EPNM management interface to trusted networks and administrators only
• Implement strict IP-based access controls for the web-based management interface
• Configure additional authentication requirements such as multi-factor authentication for accessing the management interface
• Consider disabling or restricting access to the vulnerable REST API endpoint if not required for operations until a patch is applied

# Example: Restrict EPNM management interface access via firewall
# Limit access to trusted administrator networks only
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP