CVE-2026-1682 Overview
A null pointer dereference vulnerability has been identified in Free5GC SMF (Session Management Function) up to version 4.1.0. The vulnerability exists in the HandlePfcpAssociationReleaseRequest function within the file internal/pfcp/handler/handler.go of the PFCP UDP Endpoint component. An attacker can remotely trigger this vulnerability through manipulation of PFCP (Packet Forwarding Control Protocol) messages, potentially causing a denial of service condition in 5G core network infrastructure.
Critical Impact
Remote attackers can cause denial of service by triggering a null pointer dereference in the SMF component, potentially disrupting 5G network session management operations.
Affected Products
- Free5GC SMF versions up to 4.1.0
- Free5GC deployments utilizing the PFCP UDP Endpoint component
- 5G core network implementations based on affected Free5GC versions
Discovery Timeline
- 2026-01-30 - CVE-2026-1682 published to NVD
- 2026-02-04 - Last updated in NVD database
Technical Details for CVE-2026-1682
Vulnerability Analysis
This vulnerability is a null pointer dereference issue (CWE-404: Improper Resource Shutdown or Release) in the Free5GC Session Management Function. The flaw resides in the PFCP message handling logic, specifically within the HandlePfcpAssociationReleaseRequest function. When processing maliciously crafted PFCP Association Release Request messages, the handler fails to properly validate pointer references before dereferencing them, leading to a crash condition.
The vulnerability is accessible over the network through the PFCP UDP endpoint, which is a critical component in 5G infrastructure responsible for managing packet forwarding rules between the SMF and User Plane Function (UPF). Successful exploitation requires no authentication or user interaction, making it particularly concerning for exposed 5G core network deployments.
Root Cause
The root cause stems from improper resource handling in the PFCP message processing logic. The HandlePfcpAssociationReleaseRequest function does not adequately check for null pointers before attempting to access object properties or methods. This can occur when the function receives a PFCP Association Release Request for a session or association that has already been released or was never properly initialized.
The vulnerability manifests when processing PFCP messages through the UDP endpoint at internal/pfcp/handler/handler.go. When certain edge cases or race conditions occur, the handler attempts to dereference a pointer that has not been properly validated, resulting in a null pointer dereference and subsequent crash.
Attack Vector
The attack can be launched remotely over the network targeting the PFCP UDP endpoint. An attacker would craft a malicious PFCP Association Release Request message designed to trigger the null pointer condition. The attack does not require authentication, privileged access, or user interaction.
The exploitation scenario involves:
- Identifying a Free5GC SMF instance with an exposed PFCP UDP endpoint
- Crafting a PFCP Association Release Request message that references a non-existent or improperly initialized association
- Sending the malformed message to the target endpoint
- Triggering the null pointer dereference, causing the SMF service to crash
For technical details on the vulnerability mechanism and available patches, see the GitHub Issue Discussion and the associated pull request.
Detection Methods for CVE-2026-1682
Indicators of Compromise
- Unexpected SMF service crashes or restarts in Free5GC deployments
- Anomalous PFCP Association Release Request messages in network traffic logs
- Crash dumps indicating null pointer dereference in handler.go
- Increased error rates or service unavailability in 5G session management
Detection Strategies
- Monitor PFCP UDP endpoint traffic for malformed or suspicious Association Release Request messages
- Implement application-level logging to capture PFCP message processing errors
- Deploy network intrusion detection rules targeting anomalous PFCP traffic patterns
- Set up service health monitoring for SMF components with automatic alerting on crashes
Monitoring Recommendations
- Enable verbose logging for the PFCP handler component to capture message processing details
- Configure crash dump collection and analysis for the SMF service
- Monitor system logs for segmentation faults or null pointer exceptions originating from handler.go
- Track SMF service uptime metrics and correlate with incoming PFCP traffic patterns
How to Mitigate CVE-2026-1682
Immediate Actions Required
- Review and apply the patch from the GitHub Pull Request #188
- Restrict network access to PFCP UDP endpoints using firewall rules
- Implement rate limiting on PFCP message processing to reduce attack surface
- Consider deploying the SMF behind a network security appliance for additional protection
Patch Information
A patch has been developed to address this vulnerability. The fix adds proper null pointer validation in the HandlePfcpAssociationReleaseRequest function before dereferencing pointers. Organizations should apply the patch available in the SMF Pull Request #188.
For additional context and discussion about the vulnerability and its remediation, refer to the GitHub Issue #794 and the VulDB entry.
Workarounds
- Implement network segmentation to isolate PFCP endpoints from untrusted networks
- Deploy a reverse proxy or security gateway in front of the SMF PFCP endpoint
- Enable additional input validation at the network perimeter for PFCP traffic
- Monitor and restart the SMF service automatically upon crash detection as a temporary measure
# Configuration example - Restrict PFCP UDP access via iptables
# Allow PFCP traffic only 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
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
