CVE-2023-20066: Cisco IOS XE Path Traversal Vulnerability

CVE-2023-20066 Overview

A directory traversal vulnerability exists in the web UI of Cisco IOS XE Software that could allow an authenticated, remote attacker to access files outside the intended filesystem mountpoint. This vulnerability stems from insufficient security configuration in the web UI component, enabling attackers to send crafted HTTP requests that bypass directory restrictions and gain read access to sensitive files on a restricted filesystem maintained for the web UI.

Critical Impact

Authenticated attackers can exploit this vulnerability to read sensitive configuration files and system data outside the web UI's designated filesystem boundary, potentially exposing credentials, network configurations, and other confidential information.

Affected Products

• Cisco IOS XE Software (versions 16.12.3, 17.3.2, 17.6.2 and others)
• Cisco Integrated Services Routers (1000, 1100, 4000 series)
• Cisco ASR 900, 1000, and 9000 Series Aggregation Services Routers
• Cisco Catalyst 3850, 8000, 9000 Series Switches
• Cisco Catalyst 9800 Series Wireless Controllers

Discovery Timeline

• March 23, 2023 - CVE-2023-20066 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-20066

Vulnerability Analysis

This directory traversal vulnerability (CWE-22/CWE-23) affects the web UI component of Cisco IOS XE Software. The web UI fails to properly validate user-supplied input in HTTP requests, allowing authenticated attackers to include path traversal sequences that navigate outside the web UI's designated filesystem mountpoint. While the attacker must possess valid credentials to exploit this vulnerability, the ability to read files outside the intended directory could expose sensitive system information.

The vulnerability is network-accessible, meaning attackers can exploit it remotely if they have authenticated access to the web UI. The attack requires low complexity to execute once authentication is achieved, and no user interaction is necessary beyond the attacker's own actions. The confidentiality impact is high as sensitive files can be read, though there is no ability to write files or impact system availability.

Root Cause

The root cause of this vulnerability is insufficient security configuration in the Cisco IOS XE web UI's file access controls. The web server component fails to properly sanitize path components in HTTP requests, allowing directory traversal sequences (such as ../) to escape the web UI's filesystem mountpoint. This represents a relative path traversal weakness (CWE-23) where user-controllable input is used to construct file paths without adequate validation.

Attack Vector

An authenticated attacker can exploit this vulnerability by crafting HTTP requests containing directory traversal sequences targeting the Cisco IOS XE web UI. The attack flow involves:

1. The attacker authenticates to the Cisco IOS XE web UI using valid credentials
2. The attacker crafts an HTTP request containing path traversal sequences designed to navigate outside the web UI filesystem mountpoint
3. The vulnerable web server processes the request without properly sanitizing the path components
4. The server returns the contents of files outside the intended directory structure
5. The attacker gains read access to sensitive files on the restricted filesystem

The attack is limited to read-only access on a restricted filesystem maintained for the web UI, meaning attackers cannot write files or directly execute code through this vulnerability alone.

Detection Methods for CVE-2023-20066

Indicators of Compromise

• HTTP requests to the IOS XE web UI containing unusual path traversal sequences such as ../ or URL-encoded variants like %2e%2e%2f
• Unexpected file access patterns in web server logs showing requests for paths outside normal web UI directories
• Authentication events followed by suspicious file retrieval requests targeting system configuration files
• Increased HTTP traffic from authenticated sessions accessing non-standard URL paths

Detection Strategies

• Monitor HTTP request logs for path traversal patterns including ../, ..%2f, %2e%2e/, and similar encoded sequences
• Implement web application firewall (WAF) rules to detect and block directory traversal attempts targeting IOS XE management interfaces
• Configure SIEM correlation rules to alert on authenticated users accessing unusual file paths through the web UI
• Enable detailed HTTP request logging on Cisco IOS XE devices to capture full URL paths for forensic analysis

Monitoring Recommendations

• Review web UI access logs regularly for anomalous path patterns and file access attempts
• Monitor for authentication events from unexpected source IP addresses followed by suspicious activity
• Establish baseline normal behavior for web UI usage and alert on deviations
• Implement network segmentation monitoring to detect unauthorized access to management interfaces

How to Mitigate CVE-2023-20066

Immediate Actions Required

• Apply Cisco security patches as specified in the Cisco Security Advisory
• Restrict access to the IOS XE web UI to trusted networks and administrators only
• Review web UI user accounts and remove or disable unnecessary access
• Enable detailed logging for the web UI to detect exploitation attempts

Patch Information

Cisco has released software updates that address this vulnerability. Organizations should consult the Cisco Security Advisory cisco-sa-webui-pthtrv-es7GSb9V for the specific fixed software versions for their deployed hardware and software combinations. The advisory provides detailed information on affected and fixed releases for all impacted product lines.

Workarounds

• Disable the HTTP/HTTPS web UI if not required for device management using the no ip http server and no ip http secure-server commands
• Implement access control lists (ACLs) to restrict web UI access to trusted management networks only
• Use out-of-band management networks isolated from production traffic for device administration
• Consider using alternative management methods such as SSH/CLI instead of the web UI where possible

# Example configuration to restrict web UI access
ip http access-class 10
ip http secure-server
access-list 10 permit 192.168.1.0 0.0.0.255
access-list 10 deny any log