CVE-2026-15720: Open5GS AMF NAS DoS Vulnerability

CVE-2026-15720 Overview

CVE-2026-15720 is a pre-authentication heap out-of-bounds read vulnerability in Open5GS through version 2.7.7. The flaw resides in the Access and Mobility Management Function (AMF) Non-Access Stratum (NAS) 5GS mobile-identity handler. An unauthenticated remote attacker can send a crafted NAS message to trigger the out-of-bounds read. Successful exploitation results in subscriber-wide denial of service across the affected 5G core network. The vulnerability is tracked under CWE-125: Out-of-bounds Read.

Critical Impact
A single unauthenticated NAS message can crash the AMF and disrupt service for every subscriber attached to the affected 5G core.

Affected Products

Open5GS versions up to and including 2.7.7
Open5GS AMF (Access and Mobility Management Function) component
5G core network deployments using vulnerable Open5GS builds

Discovery Timeline

2026-07-14 - CVE-2026-15720 published to NVD
2026-07-15 - Last updated in NVD database

Technical Details for CVE-2026-15720

Vulnerability Analysis

The vulnerability affects the AMF NAS 5GS mobile-identity handler in Open5GS. The AMF processes NAS signaling messages that carry subscriber identity information such as the Subscription Concealed Identifier (SUCI), 5G Globally Unique Temporary Identifier (5G-GUTI), and Permanent Equipment Identifier (PEI). During parsing of the mobile-identity information element, the handler reads memory beyond the bounds of the allocated heap buffer.

Because NAS mobile-identity messages are processed prior to authentication, an attacker does not need valid subscriber credentials. Any endpoint able to reach the AMF NAS interface can deliver the malformed message. A successful read past the buffer boundary causes the AMF process to crash, terminating signaling for all attached subscribers and preventing new registrations.

Root Cause

The root cause is missing or insufficient length validation of the mobile-identity information element within a NAS 5GS message. The parser trusts an attacker-controlled length or type field and reads adjacent heap memory beyond the allocated buffer. This falls under [CWE-125: Out-of-bounds Read].

Attack Vector

The attack vector is network-based with low complexity and no privileges or user interaction required. An attacker with reachability to the AMF NAS interface, whether through a compromised gNodeB, a rogue base station, or exposed core interfaces, sends a crafted 5GS NAS Registration Request or Identity Response containing a malformed mobile-identity IE. The AMF process crashes, producing a subscriber-wide denial of service.

No verified public proof-of-concept exploit code is available. Refer to the Open5GS GitHub Security Advisory GHSA-f4mx-3x6p-cfwp for authoritative technical details.

Detection Methods for CVE-2026-15720

Indicators of Compromise

Unexpected AMF process crashes or restarts correlated with inbound NAS Registration or Identity Response messages
Malformed 5GS NAS mobile-identity information elements with inconsistent length fields captured on the N1/N2 interface
Bursts of failed subscriber registrations across multiple gNodeBs at the same timestamp

Detection Strategies

Deploy signature-based inspection on N2 traffic to flag NAS messages with mobile-identity IEs whose declared length exceeds the containing message boundary
Monitor AMF service supervisor logs (systemd, container orchestrator) for repeated segmentation faults or abnormal exit codes in open5gs-amfd
Correlate crash events with source gNodeB identifiers to isolate the origin of malicious NAS traffic

Monitoring Recommendations

Enable core-dump collection for open5gs-amfd and forward stack traces to a centralized SIEM for triage
Track AMF availability metrics and alert on sudden drops in registered subscriber count
Capture NAS-layer packet metadata at the N2 reference point for retroactive investigation of suspected exploitation

How to Mitigate CVE-2026-15720

Immediate Actions Required

Upgrade Open5GS to a fixed release published after version 2.7.7 as identified in the vendor advisory
Restrict network reachability to the AMF NAS interface so that only trusted gNodeBs can deliver N2 traffic
Enable automated restart of the AMF process to reduce outage windows while patching is scheduled

Patch Information

Refer to the Open5GS GitHub Security Advisory GHSA-f4mx-3x6p-cfwp for the fixed version and commit references. Rebuild or redeploy affected AMF containers and binaries from the patched source tree.

Workarounds

Place the AMF behind a NAS-aware security gateway that validates mobile-identity IE lengths before forwarding to the core
Terminate N2 SCTP associations from untrusted or unauthenticated gNodeB peers using IPsec and strict peer allow-lists
Deploy multiple AMF instances behind a load balancer so that a single crash does not affect all subscribers

bash

# Configuration example: restrict AMF NGAP listener to trusted gNodeB subnet
# /etc/open5gs/amf.yaml
amf:
  ngap:
    server:
      - address: 10.10.0.5
        port: 38412
  # Enforce IPsec/allow-list at the host firewall
# iptables example limiting N2 SCTP to trusted gNodeB range
iptables -A INPUT -p sctp --dport 38412 -s 10.20.0.0/24 -j ACCEPT
iptables -A INPUT -p sctp --dport 38412 -j DROP