CVE-2026-42800: ASR1903 NULL Pointer Dereference Flaw

CVE-2026-42800 Overview

A NULL pointer dereference vulnerability has been identified in ASR1903 within ASR Lapwing_Linux on Linux, specifically affecting the ims_client modules. This vulnerability enables pointer manipulation attacks that could lead to denial of service conditions or potentially other security impacts. The vulnerability is associated with program files located at sip/utils/src/sipuri.c.

Critical Impact
This network-accessible vulnerability allows authenticated attackers to manipulate pointers through the SIP URI handling component, potentially causing system crashes or service disruptions across affected ASR Lapwing_Linux deployments.

Affected Products

ASR Lapwing_Linux (ims_client modules)
ASR1903 platform components
SIP/IMS client implementations utilizing sipuri.c

Discovery Timeline

April 30, 2026 - CVE-2026-42800 published to NVD
April 30, 2026 - Last updated in NVD database

Technical Details for CVE-2026-42800

Vulnerability Analysis

This NULL pointer dereference vulnerability (CWE-476) exists within the SIP URI parsing functionality of the ASR Lapwing_Linux IMS client. The vulnerability is network-accessible and requires low-level privileges to exploit. When triggered, the vulnerability can impact systems beyond the vulnerable component itself, potentially affecting confidentiality, integrity, and availability of the target system.

The vulnerability manifests in the sipuri.c file within the sip/utils/src/ directory, which handles SIP URI processing for the IMS client functionality. Improper validation of pointer references before dereferencing allows attackers to cause the application to access memory at address zero, leading to a crash or unexpected behavior.

Root Cause

The root cause of CVE-2026-42800 lies in insufficient NULL pointer validation within the SIP URI handling code. The sipuri.c component fails to properly verify that pointer variables contain valid memory addresses before attempting to dereference them. This oversight allows specially crafted SIP messages or URI inputs to trigger conditions where NULL pointers are accessed, causing the application to crash or behave unpredictably.

Attack Vector

The attack is network-based and can be executed remotely by authenticated users with low privileges. An attacker could craft malicious SIP URI data that, when processed by the vulnerable ims_client module, causes the NULL pointer dereference condition. The scope of this vulnerability is changed, meaning the impact extends beyond the vulnerable component to potentially affect other system resources or services.

The vulnerability can be exploited by sending specially crafted SIP protocol messages to the affected IMS client. When the vulnerable code path in sipuri.c processes malformed URI data, it may attempt to dereference a pointer that has not been properly initialized or has been set to NULL, resulting in a crash condition.

Detection Methods for CVE-2026-42800

Indicators of Compromise

Unexpected crashes or segmentation faults in IMS client processes related to SIP URI handling
Core dumps or error logs indicating NULL pointer access in sipuri.c or related SIP modules
Abnormal SIP protocol traffic containing malformed URI patterns targeting ASR1903 systems
Repeated service restarts of ims_client modules without legitimate cause

Detection Strategies

Monitor system logs for segmentation faults or NULL pointer exceptions in IMS client processes
Implement network intrusion detection rules to identify malformed SIP URI patterns
Deploy application-level monitoring for crashes in sip/utils/src/sipuri.c code paths
Enable core dump analysis to detect exploitation attempts targeting pointer manipulation

Monitoring Recommendations

Configure alerting for abnormal termination of IMS client services on ASR Lapwing_Linux systems
Implement SIP protocol inspection at network boundaries to detect potential exploit attempts
Monitor for unusual patterns in SIP URI requests that could indicate probing or exploitation
Enable verbose logging for SIP message processing to capture potential attack indicators

How to Mitigate CVE-2026-42800

Immediate Actions Required

Review the ASR Micro Security Advisory for official patch information and guidance
Restrict network access to affected IMS client services to trusted sources only
Implement network segmentation to limit the exposure of vulnerable ASR1903 systems
Monitor affected systems for signs of exploitation or unusual SIP protocol activity

Patch Information

ASR Micro has published a security advisory addressing this vulnerability. Organizations should consult the ASR Micro Security Advisory for the latest patch information, affected version details, and recommended update procedures. Apply vendor-provided patches as soon as they become available for your specific ASR Lapwing_Linux deployment.

Workarounds

Implement strict input validation at network boundaries for all SIP protocol traffic
Deploy network access controls to limit which systems can communicate with vulnerable IMS client modules
Consider temporarily disabling non-essential IMS client functionality until patches are applied
Use application firewalls or WAF rules to filter potentially malicious SIP URI patterns

bash

# Example: Network access restriction for IMS client services
# Restrict access to SIP services from trusted networks only
iptables -A INPUT -p udp --dport 5060 -s trusted_network/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 5060 -s trusted_network/24 -j ACCEPT
iptables -A INPUT -p udp --dport 5060 -j DROP
iptables -A INPUT -p tcp --dport 5060 -j DROP