CVE-2025-20165: Cisco BroadWorks Network Server DoS Flaw

CVE-2025-20165 Overview

A vulnerability in the SIP processing subsystem of Cisco BroadWorks could allow an unauthenticated, remote attacker to halt the processing of incoming SIP requests, resulting in a denial of service (DoS) condition. This vulnerability is due to improper memory handling for certain SIP requests. An attacker could exploit this vulnerability by sending a high number of SIP requests to an affected system. A successful exploit could allow the attacker to exhaust the memory allocated to the Cisco BroadWorks Network Servers that handle SIP traffic. If no memory is available, the Network Servers can no longer process incoming requests, resulting in a DoS condition that requires manual intervention to recover.

Critical Impact
Remote attackers can cause complete service disruption of SIP communications by exhausting server memory, requiring manual intervention to restore normal operations.

Affected Products

Cisco BroadWorks Network Server (Release Independent)

Discovery Timeline

January 22, 2025 - CVE-2025-20165 published to NVD
August 6, 2025 - Last updated in NVD database

Technical Details for CVE-2025-20165

Vulnerability Analysis

This vulnerability affects the SIP (Session Initiation Protocol) processing subsystem within Cisco BroadWorks Network Servers. The flaw allows unauthenticated attackers to remotely trigger a denial of service condition through improper memory handling. When exploited, the vulnerability causes memory exhaustion on servers responsible for handling SIP traffic, effectively preventing all incoming SIP request processing.

The vulnerability is classified under CWE-789 (Memory Allocation with Excessive Size Value), indicating that the system fails to properly constrain or validate memory allocation requests during SIP processing operations. This weakness allows attackers to force the allocation of excessive memory resources until the server's available memory is depleted.

Root Cause

The root cause lies in improper memory handling within the SIP processing subsystem. Specifically, the Cisco BroadWorks Network Servers do not adequately manage memory allocation when processing certain types of SIP requests. This design flaw allows memory to be consumed without proper bounds checking or resource limits, leading to memory exhaustion under sustained attack conditions.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by sending a high volume of specially crafted SIP requests to an affected Cisco BroadWorks Network Server. The attack characteristics include:

Remote exploitation - The attack can be launched from any network location with connectivity to the target SIP server
No authentication required - Attackers do not need valid credentials to initiate the attack
Traffic flooding approach - The exploit relies on sending numerous SIP requests to gradually exhaust server memory
Persistent impact - Once memory is exhausted, manual intervention is required to restore service

The attack exploits the SIP protocol's inherent design where servers must process incoming requests to determine their validity, allowing malicious requests to consume memory resources before being rejected.

Detection Methods for CVE-2025-20165

Indicators of Compromise

Abnormal increase in SIP traffic volume targeting BroadWorks Network Servers
Memory utilization alerts indicating sustained high memory consumption on SIP-handling servers
SIP service degradation or complete unresponsiveness to legitimate requests
System logs showing memory allocation failures or out-of-memory conditions

Detection Strategies

Implement network traffic monitoring to detect anomalous SIP request patterns and volume spikes
Configure memory utilization thresholds on BroadWorks Network Servers with automated alerting
Deploy SIP-aware intrusion detection systems (IDS) to identify potential DoS attack signatures
Monitor SIP server response times for degradation that may indicate resource exhaustion

Monitoring Recommendations

Establish baseline SIP traffic patterns to enable effective anomaly detection
Configure real-time monitoring of memory usage on all BroadWorks Network Server instances
Implement logging of SIP request sources to identify potential attack origins
Set up automated alerting for memory threshold violations and service availability issues

How to Mitigate CVE-2025-20165

Immediate Actions Required

Review the Cisco Security Advisory for vendor-specific guidance and patch availability
Implement rate limiting on SIP traffic at network perimeter devices
Configure SIP session limits and connection thresholds where possible
Ensure monitoring is in place to detect early signs of exploitation attempts

Patch Information

Cisco has released a security advisory addressing this vulnerability. Organizations running affected versions of Cisco BroadWorks Network Server should consult the Cisco Security Advisory for specific patch information and upgrade guidance. Apply vendor-provided patches as soon as they become available for your deployment.

Workarounds

Implement network-level rate limiting for SIP traffic to reduce the impact of flooding attacks
Configure firewall rules to restrict SIP access to known, trusted IP ranges where operationally feasible
Deploy SIP-aware load balancers to distribute traffic and mitigate concentrated attacks on individual servers
Consider implementing SIP proxy servers with traffic filtering capabilities as an additional defensive layer

bash

# Example rate limiting configuration concept (adapt to your environment)
# Configure SIP traffic rate limits on network devices
# Restrict SIP access to authorized source IP ranges
# Enable connection tracking and session limits for SIP protocol
# Monitor and alert on threshold violations