CVE-2026-1738 Overview
A vulnerability has been identified in Open5GS up to version 2.7.6 affecting the SGWC (Serving Gateway Control Plane) component. The flaw exists in the sgwc_tunnel_add function located in /src/sgwc/context.c, where manipulation of the pdr (Packet Detection Rule) argument can trigger a reachable assertion. This vulnerability can be exploited remotely over the network to cause a denial of service condition in 5G core network infrastructure.
Critical Impact
Remote attackers can crash the SGWC component of Open5GS deployments by triggering an assertion failure, potentially disrupting 5G network services and affecting mobile network availability.
Affected Products
- Open5GS versions up to 2.7.6
- SGWC (Serving Gateway Control Plane) component
- Deployments using /src/sgwc/context.c module
Discovery Timeline
- 2026-02-02 - CVE CVE-2026-1738 published to NVD
- 2026-02-03 - Last updated in NVD database
Technical Details for CVE-2026-1738
Vulnerability Analysis
This vulnerability is classified as CWE-617 (Reachable Assertion), a condition where an assertion check can be triggered by external input, causing the application to terminate abnormally. In the context of Open5GS, the sgwc_tunnel_add function in the SGWC component fails to properly validate the pdr argument before an assertion check. When a specially crafted input is provided, the assertion condition fails, causing the SGWC process to crash.
Open5GS is an open-source implementation of 5G Core and EPC (Evolved Packet Core), widely used in telecommunications research, testing environments, and some production deployments. The SGWC component handles the control plane functions for the Serving Gateway, making it a critical element in user equipment connectivity and data session management.
The vulnerability can be exploited remotely without authentication, as the attack vector is network-based. The issue report indicates that a patch has already been developed to address this vulnerability.
Root Cause
The root cause is improper input validation in the sgwc_tunnel_add function before assertion checks are performed. The function contains an assertion statement that validates the state of the pdr argument, but external inputs can reach this assertion with unexpected values. When assertions are enabled in production builds and the validation fails, the program terminates immediately rather than handling the error gracefully.
Attack Vector
The attack can be executed remotely over the network by sending malformed data that reaches the sgwc_tunnel_add function with a manipulated pdr argument. An attacker targeting Open5GS infrastructure could craft network packets that trigger the vulnerable code path, causing the assertion to fail and the SGWC service to crash. This results in a denial of service condition affecting the 5G core network's ability to handle gateway control plane operations.
The vulnerability mechanism involves the following flow: malformed input is received by the SGWC component, the input is processed and passed to sgwc_tunnel_add, the pdr argument contains unexpected values, and the assertion check fails, causing an immediate process termination. For detailed technical information about the vulnerability, refer to GitHub Issue #4261.
Detection Methods for CVE-2026-1738
Indicators of Compromise
- Unexpected crashes or restarts of the SGWC service in Open5GS deployments
- Core dump files generated by assertion failures in the sgwc_tunnel_add function
- Log entries indicating assertion failures in /src/sgwc/context.c
- Repeated service interruptions affecting 5G gateway control plane operations
Detection Strategies
- Monitor Open5GS SGWC process stability and implement alerting for unexpected terminations
- Configure crash dump collection to capture assertion failure details for forensic analysis
- Deploy network intrusion detection rules to identify malformed GTP-C or PFCP protocol messages
- Implement service health checks that detect SGWC unavailability within seconds
Monitoring Recommendations
- Enable verbose logging for the SGWC component to capture detailed error information
- Set up automated alerts for assertion failure patterns in system logs
- Monitor network traffic to the SGWC interfaces for anomalous patterns
- Implement process supervision to automatically restart crashed services while alerting administrators
How to Mitigate CVE-2026-1738
Immediate Actions Required
- Upgrade Open5GS to the latest patched version beyond 2.7.6 as indicated by the already-fixed status
- Review and apply the security patch referenced in GitHub Issue #4261
- Implement network segmentation to limit access to SGWC interfaces from untrusted networks
- Configure process supervisors to automatically restart the SGWC service if it crashes
Patch Information
The issue report is flagged as already-fixed, indicating that a patch has been developed and merged into the Open5GS repository. Organizations should update to the latest release or apply the fix from the Open5GS GitHub repository. Additional details about the fix can be found in the related GitHub issue events.
Workarounds
- Implement network access controls to restrict which systems can communicate with the SGWC component
- Deploy a Web Application Firewall or network filter to inspect and sanitize incoming traffic
- Consider disabling assertions in production builds if the vendor provides guidance (note: this may mask other issues)
- Use containerization with automatic restart policies to minimize service downtime from crashes
# Example: Configure systemd service restart policy for Open5GS SGWC
# /etc/systemd/system/open5gs-sgwcd.service.d/restart.conf
[Service]
Restart=always
RestartSec=5
StartLimitIntervalSec=60
StartLimitBurst=5
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
