CVE-2023-20116: Cisco Unified Communications Manager DoS

CVE-2023-20116 Overview

A vulnerability exists in the Administrative XML Web Service (AXL) API of Cisco Unified Communications Manager (Unified CM) and Cisco Unified Communications Manager Session Management Edition (Unified CM SME) that could allow an authenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.

This vulnerability is due to insufficient validation of user-supplied input to the web UI of the Self Care Portal. An attacker could exploit this vulnerability by sending crafted HTTP input to an affected device. A successful exploit could allow the attacker to cause a DoS condition on the affected device, potentially disrupting critical enterprise communications infrastructure.

Critical Impact

Authenticated attackers can disrupt Cisco Unified Communications Manager services through crafted HTTP requests, potentially affecting enterprise voice and video communications.

Affected Products

• Cisco Unified Communications Manager 11.5(1.10000.6)
• Cisco Unified Communications Manager 12.0(1.10000.10)
• Cisco Unified Communications Manager 12.5(1.10000.22)
• Cisco Unified Communications Manager 14.0(1.10000.20)
• Cisco Unified Communications Manager Session Management Edition (all above versions)

Discovery Timeline

• 2023-06-28 - CVE-2023-20116 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-20116

Vulnerability Analysis

CVE-2023-20116 is classified under CWE-835 (Loop with Unreachable Exit Condition), commonly known as an infinite loop vulnerability. The flaw resides in how the Administrative XML Web Service (AXL) API processes user-supplied input through the Self Care Portal web interface.

When exploited, the vulnerability causes the affected service to enter a state where it cannot properly process subsequent requests, leading to service unavailability. The attack requires network access to the vulnerable system and valid user credentials, though only requires a low privilege level to execute.

The vulnerability requires user interaction for successful exploitation, which somewhat limits the attack surface. However, given the critical nature of unified communications infrastructure in enterprise environments, any service disruption can have significant business impact.

Root Cause

The root cause of this vulnerability is insufficient validation of user-supplied input to the Self Care Portal web interface. The AXL API fails to properly sanitize or validate HTTP input before processing, allowing an attacker to supply crafted input that triggers an infinite loop condition (CWE-835). This causes the service to become unresponsive, resulting in a denial of service condition.

Attack Vector

The attack vector for CVE-2023-20116 is network-based, requiring the attacker to have authenticated access to the Cisco Unified Communications Manager. The exploitation flow involves:

1. Attacker authenticates to the Self Care Portal with valid credentials
2. Attacker crafts malicious HTTP input designed to trigger the input validation flaw
3. The crafted request is sent to the AXL API endpoint
4. Insufficient validation allows the input to trigger an infinite loop
5. The affected device enters a DoS condition, disrupting communications services

The vulnerability does not impact confidentiality or integrity but has a high impact on availability. User interaction is required for successful exploitation, which may involve social engineering techniques or exploitation during routine administrative tasks.

Detection Methods for CVE-2023-20116

Indicators of Compromise

• Unusual increase in HTTP requests to the Self Care Portal from authenticated sessions
• Service unresponsiveness or degraded performance on Cisco Unified CM systems
• High CPU utilization on affected devices without corresponding legitimate workload
• Repeated authentication events followed by service disruptions

Detection Strategies

• Monitor AXL API access logs for anomalous request patterns or malformed HTTP input
• Implement alerting for service availability metrics on Unified CM systems
• Deploy network-based intrusion detection rules targeting the Self Care Portal endpoints
• Track authenticated session behavior for unusual activity patterns

Monitoring Recommendations

• Enable verbose logging on the Self Care Portal and AXL API components
• Configure SNMP or syslog monitoring for service state changes on Unified CM devices
• Implement SentinelOne Singularity platform for real-time endpoint monitoring and behavioral analysis
• Establish baseline metrics for normal AXL API usage to identify deviations

How to Mitigate CVE-2023-20116

Immediate Actions Required

• Review and apply the latest Cisco security patches for Unified Communications Manager
• Restrict network access to the Self Care Portal to trusted IP ranges
• Audit user accounts with access to the AXL API and enforce principle of least privilege
• Monitor for exploitation attempts using the detection strategies outlined above

Patch Information

Cisco has released security patches addressing this vulnerability. Administrators should consult the Cisco Security Advisory for detailed patch information, affected version matrices, and upgrade guidance specific to their deployment.

Organizations running the following versions should prioritize patching:

• Version 11.5(1.10000.6)
• Version 12.0(1.10000.10)
• Version 12.5(1.10000.22)
• Version 14.0(1.10000.20)

Both standard and Session Management Edition deployments are affected.

Workarounds

• Implement network segmentation to limit access to the Self Care Portal from untrusted networks
• Use access control lists (ACLs) to restrict AXL API access to authorized administrative systems only
• Consider temporarily disabling Self Care Portal functionality if not business-critical until patches can be applied
• Deploy web application firewall (WAF) rules to filter potentially malicious HTTP input patterns

# Example ACL configuration to restrict Self Care Portal access
# Consult Cisco documentation for your specific deployment
# Restrict access to administrative interfaces to trusted management networks only
access-list CUCM-MGMT permit tcp <trusted-admin-network> <wildcard-mask> host <cucm-ip> eq 443
access-list CUCM-MGMT deny tcp any host <cucm-ip> eq 443