CVE-2026-1739 Overview
A null pointer dereference vulnerability has been identified in the Free5GC Policy Control Function (PCF) component, affecting versions up to and including 1.4.1. The vulnerability exists within the HandleCreateSmPolicyRequest function located in internal/sbi/processor/smpolicy.go. An attacker can exploit this flaw remotely to cause a denial of service condition by triggering the null pointer dereference through crafted network requests.
Critical Impact
Remote attackers can cause service disruption in 5G core network infrastructure by crashing the PCF component, potentially affecting mobile network policy management and subscriber services.
Affected Products
- Free5GC PCF version 1.4.1 and earlier
- Free5GC 5G core network deployments utilizing the vulnerable PCF component
- Systems running the affected smpolicy.go request handler
Discovery Timeline
- 2026-02-02 - CVE CVE-2026-1739 published to NVD
- 2026-02-03 - Last updated in NVD database
Technical Details for CVE-2026-1739
Vulnerability Analysis
This vulnerability is classified as a null pointer dereference (CWE-404: Improper Resource Shutdown or Release) affecting the Policy Control Function in Free5GC, an open-source 5G core network implementation. The flaw resides in the session management policy handling code, specifically within the HandleCreateSmPolicyRequest function.
When the PCF receives a malformed or specially crafted SmPolicy creation request, the code fails to properly validate input parameters before dereferencing them. This results in an attempt to access memory through a null pointer, causing the application to crash. Given that the PCF is a critical component responsible for policy decisions in 5G networks, including QoS enforcement and session management, a successful exploit could disrupt mobile network services.
The vulnerability is remotely exploitable over the network without requiring authentication or user interaction. The exploit has been publicly disclosed, increasing the risk of active exploitation in vulnerable deployments.
Root Cause
The root cause of this vulnerability is insufficient input validation in the HandleCreateSmPolicyRequest function within internal/sbi/processor/smpolicy.go. The code does not perform adequate null checks on request parameters before processing, allowing a null pointer to be dereferenced when handling malformed SmPolicy requests. This represents a failure to follow defensive programming practices when handling external input in a network-exposed service.
Attack Vector
The attack can be executed remotely over the network by sending specially crafted HTTP requests to the PCF's Service-Based Interface (SBI). The attack characteristics include:
- Remote Execution: The vulnerability is exploitable from a network-accessible position without requiring local access to the target system
- No Authentication Required: Attackers do not need valid credentials to trigger the vulnerability
- No User Interaction: Exploitation does not require any action from legitimate users
- Denial of Service Impact: Successful exploitation results in service crash, causing availability loss
The vulnerability manifests when the PCF processes SmPolicy creation requests that contain missing or null fields that the handler expects to be populated. When the code attempts to access properties of these null objects, the application crashes. For detailed technical analysis, refer to the GitHub Issue #803 which contains the vulnerability disclosure.
Detection Methods for CVE-2026-1739
Indicators of Compromise
- Unexpected crashes or restarts of the Free5GC PCF service
- Error logs containing null pointer dereference or panic messages in the smpolicy.go handler
- Anomalous HTTP requests to the PCF SBI endpoint targeting SmPolicy creation APIs
- Service availability interruptions affecting policy control functions
Detection Strategies
- Monitor PCF service health and implement alerting for unexpected process terminations or restarts
- Implement application-level logging to capture detailed request information for SmPolicy API endpoints
- Deploy network intrusion detection rules to identify malformed SmPolicy creation requests
- Establish baseline metrics for PCF API request patterns and alert on statistical anomalies
Monitoring Recommendations
- Enable verbose logging for the PCF component to capture request details and error conditions
- Implement service mesh or API gateway monitoring to track request patterns to the PCF SBI
- Configure container orchestration health checks to detect and report PCF crashes promptly
- Review system logs for panic or crash dump entries related to the smpolicy.go module
How to Mitigate CVE-2026-1739
Immediate Actions Required
- Apply the security patch identified by commit df535f5524314620715e842baf9723efbeb481a7 immediately
- Review network segmentation to restrict access to the PCF SBI interface from untrusted networks
- Implement API gateway or web application firewall rules to validate SmPolicy requests before forwarding
- Monitor for signs of exploitation while preparing to deploy the patch
Patch Information
The Free5GC project has released a patch to address this vulnerability. The fix is available in commit df535f5524314620715e842baf9723efbeb481a7 within the PCF repository. Organizations should update to a patched version of the PCF component. The patch can also be reviewed in Pull Request #62 which contains the code changes addressing the null pointer dereference.
Workarounds
- Restrict network access to the PCF SBI interface using firewall rules or network policies to allow only trusted network functions
- Implement an API gateway or reverse proxy with input validation to filter malformed requests before they reach the PCF
- Deploy rate limiting on the PCF endpoints to reduce the impact of potential denial of service attempts
- Consider temporarily taking the PCF offline in non-production environments until the patch can be applied
# Example: Restrict access to PCF SBI interface using iptables
# Replace PCF_IP and PCF_PORT with your deployment values
iptables -A INPUT -p tcp --dport 8000 -s trusted_network_cidr -j ACCEPT
iptables -A INPUT -p tcp --dport 8000 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
