CVE-2026-1973 Overview
A null pointer dereference vulnerability has been identified in Free5GC, an open-source 5G core network implementation. The vulnerability affects the establishPfcpSession function within the Session Management Function (SMF) component. When exploited, an attacker can cause a denial of service condition by triggering a null pointer dereference, potentially disrupting 5G network operations. The exploit has been publicly disclosed and may be utilized by threat actors targeting 5G infrastructure.
Critical Impact
This vulnerability allows remote attackers to cause denial of service conditions in 5G core network deployments using Free5GC, potentially disrupting mobile network services and session management capabilities.
Affected Products
- Free5GC versions up to and including 4.1.0
- Free5GC SMF (Session Management Function) component
Discovery Timeline
- 2026-02-06 - CVE CVE-2026-1973 published to NVD
- 2026-02-09 - Last updated in NVD database
Technical Details for CVE-2026-1973
Vulnerability Analysis
This vulnerability is classified as a Null Pointer Dereference (CWE-476) with an associated Improper Resource Shutdown or Release weakness (CWE-404). The flaw exists within the establishPfcpSession function of the SMF component, which is responsible for managing Packet Forwarding Control Protocol (PFCP) sessions in the 5G core network.
The SMF component handles session establishment between the 5G core and User Plane Function (UPF), making it a critical element in the network architecture. When processing certain malformed or unexpected input during PFCP session establishment, the function fails to properly validate pointer references before dereferencing them, leading to a null pointer dereference condition.
The vulnerability can be exploited remotely over the network without requiring authentication or user interaction. While the impact is limited to availability (denial of service), the attack can disrupt critical 5G network functions.
Root Cause
The root cause of this vulnerability is improper input validation and missing null pointer checks in the establishPfcpSession function. The code fails to verify that pointers are valid before attempting to access the referenced memory locations. This type of defensive programming oversight is particularly dangerous in network-facing components that process untrusted external input.
Attack Vector
The attack can be launched remotely over the network by sending specially crafted PFCP session establishment requests to the SMF component. The attacker does not require any privileges or authentication to trigger the vulnerability. Upon receiving the malicious request, the SMF component attempts to process it, encounters a null pointer, and crashes or becomes unresponsive.
The vulnerability affects the availability of the service without impacting confidentiality or integrity. For technical details regarding the specific exploitation method, refer to the GitHub Free5GC Issue #815 where the vulnerability was publicly disclosed.
Detection Methods for CVE-2026-1973
Indicators of Compromise
- Unexpected crashes or restarts of the Free5GC SMF service
- PFCP session establishment failures logged in SMF component logs
- Unusual network traffic patterns targeting PFCP endpoints (typically UDP port 8805)
- Core dumps or segmentation fault errors in SMF process logs
Detection Strategies
- Monitor Free5GC SMF service availability and implement automated restart detection
- Configure network intrusion detection systems to identify malformed PFCP packets
- Enable detailed logging for the SMF component to capture session establishment anomalies
- Deploy application performance monitoring to detect sudden service degradation
Monitoring Recommendations
- Implement health checks for the SMF component with alerting on service unavailability
- Monitor system logs for segmentation fault or null pointer dereference errors
- Track PFCP session establishment success/failure ratios for anomaly detection
- Set up network flow analysis to identify potential DoS attack patterns against the SMF
How to Mitigate CVE-2026-1973
Immediate Actions Required
- Upgrade Free5GC to a patched version when available
- Review and apply the fix from GitHub SMF Pull Request #189
- Implement network segmentation to restrict access to the SMF component
- Configure rate limiting on PFCP endpoints to mitigate potential DoS attacks
Patch Information
A patch addressing this vulnerability has been submitted via GitHub SMF Pull Request #189. Organizations running affected versions of Free5GC should review the pull request and apply the fix to their deployments. It is recommended to thoroughly test the patch in a non-production environment before deploying to production 5G core networks.
For additional technical details, refer to the GitHub Free5GC Issue #815 and the VulDB entry for this vulnerability.
Workarounds
- Deploy a Web Application Firewall or network firewall to filter malicious PFCP traffic
- Implement service redundancy with automatic failover for the SMF component
- Restrict network access to the SMF component to only trusted UPF and control plane nodes
- Enable process monitoring with automatic restart capabilities to minimize service disruption
# Example: Restrict PFCP access using iptables
# Only allow PFCP traffic from trusted UPF addresses
iptables -A INPUT -p udp --dport 8805 -s <trusted_upf_ip> -j ACCEPT
iptables -A INPUT -p udp --dport 8805 -j DROP
# Enable automatic service restart with systemd
systemctl enable free5gc-smf
systemctl edit free5gc-smf --force
# Add restart configuration:
# [Service]
# Restart=always
# RestartSec=5
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
