CVE-2026-4988 Overview
A denial of service vulnerability has been discovered in Open5GS 2.7.6, an open-source implementation of 5G Core and EPC (Evolved Packet Core). This security flaw affects the CCA (Credit-Control-Answer) Message Handler component, specifically the smf_gx_cca_cb, smf_gy_cca_cb, and smf_s6b functions within the SMF (Session Management Function). Successful exploitation through manipulation of these handlers can result in service disruption, potentially impacting 5G network operations.
Critical Impact
Remote attackers can cause denial of service conditions in Open5GS 5G Core infrastructure by targeting the CCA Message Handler, potentially disrupting mobile network services for connected devices.
Affected Products
- Open5GS version 2.7.6
- SMF (Session Management Function) component
- CCA Message Handler (Gx, Gy, and S6b interfaces)
Discovery Timeline
- 2026-03-27 - CVE-2026-4988 published to NVD
- 2026-03-30 - Last updated in NVD database
Technical Details for CVE-2026-4988
Vulnerability Analysis
This vulnerability is classified under CWE-404 (Improper Resource Shutdown or Release), indicating that the affected functions fail to properly manage resources during CCA message processing. The flaw exists within the SMF component of Open5GS, which handles session management for 5G networks.
The vulnerable functions (smf_gx_cca_cb, smf_gy_cca_cb, and smf_s6b) are callback handlers for Diameter protocol messages used in policy and charging control. The Gx interface handles policy control between the SMF and PCF (Policy Control Function), while the Gy interface manages online charging, and S6b handles authentication for trusted non-3GPP access.
When specially crafted CCA messages are processed by these handlers, improper resource management can lead to service degradation or complete denial of service. The attack requires network access but involves high complexity, making successful exploitation difficult to achieve consistently.
Root Cause
The root cause stems from improper resource shutdown or release (CWE-404) within the CCA message callback functions. When processing malformed or malicious CCA responses, the SMF component fails to properly release allocated resources or handle error conditions, leading to resource exhaustion or service crashes.
The callback functions for Gx, Gy, and S6b interfaces do not implement adequate validation and cleanup mechanisms when encountering unexpected message formats or state conditions during Diameter protocol exchanges.
Attack Vector
The attack can be launched remotely over the network by sending manipulated CCA messages to the Open5GS SMF component. An attacker with network access to the Diameter interfaces can craft malicious Credit-Control-Answer messages targeting the vulnerable callback handlers.
Due to the high attack complexity noted in the CVSS 4.0 assessment, successful exploitation requires specific conditions to be met:
- Network access to the SMF's Diameter interfaces (Gx, Gy, or S6b)
- Knowledge of the target's Diameter endpoint configuration
- Ability to craft valid Diameter protocol messages with malicious payloads
The exploit has been publicly disclosed through GitHub Issue #4342, providing details about the vulnerability and its exploitation. Additional technical information is available through the VulDB entry.
Detection Methods for CVE-2026-4988
Indicators of Compromise
- Unexpected SMF process crashes or restarts in Open5GS deployments
- Elevated error rates in Diameter protocol exchanges on Gx, Gy, or S6b interfaces
- Abnormal memory consumption patterns in the SMF component
- Unusual CCA message patterns or malformed Diameter AVPs in network traffic
Detection Strategies
- Monitor Open5GS SMF logs for repeated callback failures or resource allocation errors in smf_gx_cca_cb, smf_gy_cca_cb, or smf_s6b functions
- Implement Diameter protocol inspection to detect malformed or suspicious CCA messages
- Deploy network-based anomaly detection for traffic patterns targeting the SMF Diameter interfaces
- Configure process monitoring to alert on SMF service interruptions or abnormal resource usage
Monitoring Recommendations
- Enable detailed logging for the SMF component's Diameter message handlers
- Set up automated alerting for SMF process failures or service unavailability
- Monitor system resource utilization (memory, CPU) on hosts running Open5GS SMF
- Track Diameter transaction success/failure ratios for early detection of exploitation attempts
How to Mitigate CVE-2026-4988
Immediate Actions Required
- Review the GitHub Issue #4342 for the latest remediation guidance from Open5GS maintainers
- Restrict network access to SMF Diameter interfaces using firewall rules to limit exposure to trusted peers only
- Implement rate limiting on Diameter protocol connections to mitigate potential DoS impact
- Monitor Open5GS releases for patches addressing CVE-2026-4988
Patch Information
As of the last NVD update on 2026-03-30, users should monitor the Open5GS GitHub repository for official patches addressing this vulnerability. Check the project's release notes and security advisories for updates to version 2.7.6 or newer releases containing the fix.
Workarounds
- Implement network segmentation to isolate Diameter interfaces from untrusted networks
- Deploy a Diameter Edge Agent (DEA) or Diameter Routing Agent (DRA) with message filtering capabilities to inspect and validate CCA messages before they reach the SMF
- Configure connection limits and timeouts on Diameter peer connections to reduce impact of potential attacks
- Consider deploying redundant SMF instances to maintain service availability during potential exploitation attempts
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
