CVE-2022-20697: Cisco IOS Software DoS Vulnerability

CVE-2022-20697 Overview

A vulnerability in the web services interface of Cisco IOS Software and Cisco IOS XE Software could allow an authenticated, remote attacker to cause a denial of service (DoS) condition. This vulnerability is due to improper resource management in the HTTP server code. An attacker could exploit this vulnerability by sending a large number of HTTP requests to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.

Critical Impact

Successful exploitation allows an authenticated remote attacker to force affected Cisco network devices to reload, causing network outages and service disruptions across enterprise infrastructure.

Affected Products

• Cisco IOS Software (multiple versions including 15.1, 15.2, 15.3, and 15.9 releases)
• Cisco IOS XE Software (versions 3.11.3ae, 3.11.3e, 3.11.4e)
• Network devices running vulnerable HTTP server configurations

Discovery Timeline

• April 15, 2022 - CVE-2022-20697 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-20697

Vulnerability Analysis

This vulnerability resides in the HTTP server code of Cisco IOS and IOS XE Software, which provides web-based management interfaces for network device administration. The flaw stems from improper resource management (CWE-772: Missing Release of Resource after Effective Lifetime) combined with insufficient control flow management (CWE-691). When the HTTP server receives and processes requests, it fails to properly manage allocated resources, leading to resource exhaustion under sustained request loads.

The network-accessible nature of this vulnerability means that any authenticated attacker with network access to the device's web services interface can trigger the condition. No user interaction is required beyond the initial authentication, and the impact extends beyond the vulnerable component itself, affecting the entire device's availability.

Root Cause

The root cause is improper resource management within the HTTP server implementation. When processing HTTP requests, the server allocates resources but fails to release them properly after the request lifecycle completes. This resource handling deficiency, classified under CWE-772 (Missing Release of Resource after Effective Lifetime), allows an attacker to systematically consume available resources by sending numerous HTTP requests. The cumulative effect of unreleased resources eventually exhausts the device's capacity, triggering a reload to recover.

Attack Vector

The attack leverages network access to the web services interface of affected Cisco devices. An authenticated attacker initiates the exploit by establishing a session with the HTTP server and then sending a high volume of HTTP requests to the target device. The improper resource management in the server code causes resources to accumulate without being released. As resource exhaustion progresses, the device becomes unstable and ultimately reloads to recover from the depleted state.

The attack does not require elevated privileges beyond standard authentication to the web services interface, and the low complexity of the attack makes it accessible to attackers with basic knowledge of HTTP request generation. The changed scope indicates that the availability impact extends beyond the web services component to affect the entire network device and dependent services.

Detection Methods for CVE-2022-20697

Indicators of Compromise

• Unexpected device reloads or restarts without scheduled maintenance
• High volume of HTTP requests in device logs from single or multiple authenticated sources
• Resource exhaustion warnings or memory-related syslog messages preceding device reloads
• Abnormal patterns in web services access logs showing rapid successive requests

Detection Strategies

• Monitor device syslog messages for unexpected reload events and correlate with HTTP server activity
• Implement network traffic analysis to detect anomalous volumes of HTTP requests directed at device management interfaces
• Configure SNMP traps or monitoring for device uptime changes and reload events
• Review authentication logs for suspicious patterns of authenticated sessions followed by high request rates

Monitoring Recommendations

• Enable detailed logging on Cisco IOS/IOS XE web services interfaces to capture request patterns
• Deploy network monitoring solutions to baseline normal HTTP traffic to management interfaces and alert on deviations
• Configure device health monitoring to track memory and resource utilization trends
• Implement centralized logging to correlate HTTP server events across multiple devices for attack pattern detection

How to Mitigate CVE-2022-20697

Immediate Actions Required

• Apply security patches from Cisco as detailed in the Cisco Security Advisory
• Restrict access to the web services interface using access control lists (ACLs) to limit authenticated users to trusted IP addresses
• Evaluate the necessity of the HTTP server feature and disable it if not required for operations
• Implement rate limiting where supported to reduce the impact of high-volume request attacks

Patch Information

Cisco has released security updates addressing this vulnerability. Affected organizations should consult the Cisco Security Advisory (cisco-sa-http-dos-svOdkdBS) for specific fixed software versions applicable to their deployment. The advisory provides detailed information on identifying vulnerable versions and obtaining appropriate updates for Cisco IOS and IOS XE Software.

Workarounds

• Disable the HTTP server on affected devices if web-based management is not required using the no ip http server and no ip http secure-server commands
• Implement infrastructure ACLs to restrict HTTP/HTTPS access to management interfaces from trusted networks only
• Use alternative management methods such as SSH for device administration where possible
• Segment management interfaces on separate VLANs with strict access controls

# Configuration example - Disable HTTP server if not needed
configure terminal
no ip http server
no ip http secure-server
end
write memory

# Alternative: Restrict HTTP access to trusted management network
configure terminal
ip http access-class 10
access-list 10 permit 192.168.100.0 0.0.0.255
access-list 10 deny any
end
write memory