CVE-2026-8288 Overview
CVE-2026-8288 is a denial-of-service vulnerability in Open5GS versions up to 2.7.7. The flaw resides in the gsm_handle_pdu_session_modification_qos_flow_descriptions function within src/smf/gsm-handler.c, a component of the Session Management Function (SMF). An authenticated remote attacker can manipulate the n1SmMsg argument to trigger improper resource handling, classified under [CWE-404] (Improper Resource Shutdown or Release). The exploit has been publicly disclosed, though a fix pull request awaits acceptance upstream. Open5GS is an open-source implementation of 5G Core and EPC, widely used in private mobile networks and research environments.
Critical Impact
Remote authenticated attackers can disrupt SMF availability by sending crafted PDU session modification messages, affecting subscriber session management in 5G core deployments.
Affected Products
- Open5GS versions up to and including 2.7.7
- Open5GS SMF component (src/smf/gsm-handler.c)
- 5G Core deployments using vulnerable Open5GS builds
Discovery Timeline
- 2026-05-11 - CVE-2026-8288 published to NVD
- 2026-05-12 - Last updated in NVD database
Technical Details for CVE-2026-8288
Vulnerability Analysis
The vulnerability affects the Open5GS Session Management Function, which handles PDU session establishment and modification in 5G core networks. The function gsm_handle_pdu_session_modification_qos_flow_descriptions processes Quality of Service (QoS) flow descriptions inside PDU session modification messages.
When the function parses the n1SmMsg parameter from an attacker-controlled input, it fails to properly handle or release resources under specific manipulated conditions. This improper resource shutdown ([CWE-404]) results in the SMF process becoming unavailable.
The attack requires network reachability to the SMF and low-level privileges, consistent with an authenticated subscriber or compromised access network component. No user interaction is required, and the exploit has been publicly disclosed.
Root Cause
The root cause is improper resource shutdown or release in the QoS flow description handler. When processing a malformed or manipulated n1SmMsg argument, the function does not gracefully recover or release allocated resources, leading to a denial-of-service condition on the SMF.
Attack Vector
The attack vector is network-based. An attacker with low privileges sends a crafted PDU session modification request containing a manipulated n1SmMsg to the SMF. Because the SMF is a central control-plane function in 5G core architecture, a successful attack disrupts session management for connected subscribers.
Technical details and discussion are available in GitHub Issue #4452 and VulDB #362585.
Detection Methods for CVE-2026-8288
Indicators of Compromise
- SMF process crashes, restarts, or unresponsiveness following PDU session modification requests
- Abnormal volume of PDU session modification messages from a single or small set of subscribers
- Malformed n1SmMsg payloads in SMF logs containing unexpected QoS flow descriptions
- Subscriber-reported session loss correlated with control-plane disruptions
Detection Strategies
- Inspect SMF application logs for parser errors or exceptions within gsm_handle_pdu_session_modification_qos_flow_descriptions
- Monitor SMF process health metrics, including restart counts and memory consumption trends
- Apply deep packet inspection on N1/N11 reference points to flag abnormal PDU session modification structures
Monitoring Recommendations
- Enable verbose logging on the SMF during patch validation to capture crash signatures
- Track per-subscriber rates of PDU session modification requests and alert on anomalies
- Correlate SMF availability metrics with upstream access and mobility function (AMF) events
How to Mitigate CVE-2026-8288
Immediate Actions Required
- Restrict network access to the SMF control-plane interfaces to trusted 5G core elements only
- Apply rate limiting on PDU session modification requests at the AMF or service-based interface
- Monitor the upstream Open5GS Pull Request #4513 and apply the fix once merged
- Maintain SMF process supervision to automatically restart the service if it terminates
Patch Information
As of the last NVD update on 2026-05-12, no official patched release is available. A proposed fix is tracked in Open5GS Pull Request #4513 and awaits acceptance. Operators building Open5GS from source can review the pull request and apply the patch manually after validating it in a non-production environment.
Workarounds
- Deploy the SMF behind a security gateway that validates 5G NAS message structure before forwarding
- Segment the 5G core network to limit which subscribers and network elements can reach the SMF
- Enable automatic process recovery for the SMF to minimize downtime if the service is crashed
- Track availability through external health checks until the upstream patch is integrated
# Example: enable automatic SMF restart via systemd override
sudo systemctl edit open5gs-smfd
# Add the following lines:
# [Service]
# Restart=always
# RestartSec=5
sudo systemctl daemon-reload
sudo systemctl restart open5gs-smfd
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
