CVE-2023-20259 Overview
A vulnerability in an API endpoint of multiple Cisco Unified Communications Products could allow an unauthenticated, remote attacker to cause high CPU utilization, which could impact access to the web-based management interface and cause delays with call processing. This API is not used for device management and is unlikely to be used in normal operations of the device.
This vulnerability is due to improper API authentication and incomplete validation of the API request. An attacker could exploit this vulnerability by sending a crafted HTTP request to a specific API on the device. A successful exploit could allow the attacker to cause a denial of service (DoS) condition due to high CPU utilization, which could negatively impact user traffic and management access. When the attack stops, the device will recover without manual intervention.
Critical Impact
Unauthenticated remote attackers can cause denial of service conditions affecting call processing and management access across critical enterprise communications infrastructure.
Affected Products
- Cisco Emergency Responder 14su3
- Cisco Prime Collaboration Deployment 14su3
- Cisco Unified Communications Manager 12.5(1)su7 and 14su3
- Cisco Unified Communications Manager IM & Presence Service 12.5(1)su7 and 14su3
- Cisco Unity Connection 14su3
Discovery Timeline
- October 4, 2023 - CVE-2023-20259 published to NVD
- November 21, 2024 - Last updated in NVD database
Technical Details for CVE-2023-20259
Vulnerability Analysis
CVE-2023-20259 is classified as a Resource Exhaustion vulnerability (CWE-400) affecting the API endpoint of multiple Cisco Unified Communications products. The vulnerability allows unauthenticated remote attackers to trigger high CPU utilization by sending specially crafted HTTP requests to a vulnerable API endpoint.
The attack is network-based and requires no privileges or user interaction, making it particularly dangerous in enterprise environments where Cisco Unified Communications products are often internet-facing or accessible from broad network segments. While the vulnerability does not compromise confidentiality or integrity, the availability impact is significant—affecting both user traffic (call processing) and administrative access to the web-based management interface.
Notably, the affected API is not used for device management and is unlikely to be utilized during normal device operations, which may reduce the likelihood of detection through routine monitoring. The device will recover automatically once the attack ceases, indicating that the DoS condition is transient and does not cause permanent damage to the system.
Root Cause
The root cause of this vulnerability stems from two related issues: improper API authentication and incomplete validation of API requests. The affected API endpoint fails to properly authenticate incoming requests, allowing unauthenticated users to interact with the API. Additionally, the API does not adequately validate request parameters, enabling malformed or specially crafted requests to consume excessive CPU resources.
This combination of authentication bypass and input validation flaws creates conditions where an attacker can repeatedly submit resource-intensive requests without authorization, leading to CPU exhaustion and subsequent denial of service.
Attack Vector
The attack vector for CVE-2023-20259 is network-based, requiring the attacker to have network access to the vulnerable Cisco Unified Communications product. The exploitation process involves:
Reconnaissance: The attacker identifies a target running a vulnerable version of Cisco Unified Communications Manager, Emergency Responder, Prime Collaboration Deployment, IM & Presence Service, or Unity Connection.
Crafted Request Submission: The attacker sends specially crafted HTTP requests to the specific vulnerable API endpoint. These requests are designed to trigger intensive processing operations on the server.
Resource Exhaustion: The device processes these malformed requests, consuming excessive CPU resources. As CPU utilization increases, legitimate users experience degraded service quality.
Service Impact: The denial of service manifests as delays in call processing and reduced accessibility to the web-based management interface, impacting both end-users and administrators.
The attack does not require authentication, making it accessible to any attacker with network connectivity to the target system. For detailed technical information about the specific API endpoint and request format, refer to the Cisco Security Advisory.
Detection Methods for CVE-2023-20259
Indicators of Compromise
- Unusual spikes in CPU utilization on Cisco Unified Communications products without corresponding legitimate traffic increases
- Multiple HTTP requests to uncommonly used API endpoints from single or distributed source IP addresses
- User reports of call processing delays or dropped connections
- Administrators experiencing slow or unresponsive web-based management interfaces
- Abnormal HTTP request patterns in access logs targeting specific API endpoints
Detection Strategies
- Implement network-based intrusion detection rules to identify high-volume HTTP requests targeting Cisco UC API endpoints
- Configure CPU utilization thresholds with alerting on Cisco Unified Communications appliances to detect resource exhaustion attacks
- Monitor web server access logs for anomalous request patterns, particularly to non-standard or administrative API endpoints
- Deploy behavioral analysis tools to baseline normal API usage and alert on deviations
Monitoring Recommendations
- Enable SNMP monitoring for CPU and memory utilization metrics on all affected Cisco UC products
- Implement centralized logging with real-time correlation to identify attack patterns across multiple systems
- Configure alerting for web-based management interface availability degradation
- Review access logs periodically for unauthorized API access attempts from unexpected source addresses
How to Mitigate CVE-2023-20259
Immediate Actions Required
- Review the Cisco Security Advisory for specific fixed software versions and upgrade guidance
- Identify all instances of affected Cisco Unified Communications products in your environment and determine their current software versions
- Prioritize patching for internet-facing or externally accessible Cisco UC deployments
- Implement network access controls to restrict API endpoint access to authorized management networks only
Patch Information
Cisco has released software updates that address this vulnerability. Organizations should consult the Cisco Security Advisory (cisco-sa-cucm-apidos-PGsDcdNF) for detailed information on fixed software releases for each affected product. The advisory provides specific version information for:
- Cisco Emergency Responder
- Cisco Prime Collaboration Deployment
- Cisco Unified Communications Manager
- Cisco Unified Communications Manager IM & Presence Service
- Cisco Unity Connection
Workarounds
- Implement firewall rules or access control lists to restrict access to the vulnerable API endpoint from untrusted networks
- Deploy a web application firewall (WAF) or reverse proxy to filter and rate-limit requests to Cisco UC API endpoints
- Segment Cisco Unified Communications infrastructure on isolated network segments with strict ingress/egress controls
- Monitor and implement IP-based blocking for source addresses exhibiting attack patterns
# Example ACL configuration to restrict API access (adapt to your environment)
# Restrict HTTP/HTTPS access to management interfaces from trusted networks only
access-list CUCM_MGMT_ACL permit tcp 10.0.0.0 0.255.255.255 host 192.168.1.100 eq 443
access-list CUCM_MGMT_ACL deny tcp any host 192.168.1.100 eq 443
access-list CUCM_MGMT_ACL deny tcp any host 192.168.1.100 eq 80
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
