CVE-2026-48131: VPN Service IKE DoS Vulnerability

CVE-2026-48131 Overview

CVE-2026-48131 affects the Check Point VPN service handling of Internet Key Exchange (IKE) fragments on UDP port 500. The service mishandles unexpected IKE fragment values received during the early stage of a connection attempt. This processing flaw causes the VPN service to terminate unexpectedly, resulting in denial of service and temporary disruption of VPN-related functionality. The issue is classified as a heap-based buffer overflow [CWE-122] and is reachable remotely without authentication.

Critical Impact
Remote unauthenticated attackers can trigger VPN service termination by sending malformed IKE fragments to UDP port 500, disrupting site-to-site and remote access VPN connectivity.

Affected Products

Check Point VPN service (refer to vendor advisory sk184981 for affected versions)
Gateways exposing IKE on UDP port 500
Remote Access and Site-to-Site VPN deployments

Discovery Timeline

2026-05-26 - CVE-2026-48131 published to NVD
2026-05-26 - Last updated in NVD database

Technical Details for CVE-2026-48131

Vulnerability Analysis

The vulnerability resides in the IKE fragment parsing logic of the Check Point VPN service. IKE fragmentation, defined in RFC 7383, splits large IKE messages into smaller UDP datagrams to traverse networks with constrained MTU. The service processes fragment metadata before the IKE security association is established, exposing the parser to unauthenticated input. An unexpected fragment value triggers a heap-based memory corruption condition [CWE-122] that crashes the service. The flaw manifests during the early connection stage, before peer authentication, making it reachable from any network endpoint that can deliver UDP traffic to port 500. According to the Exploit Prediction Scoring System, the EPSS data places this issue at the low end of the percentile distribution, but exposure of VPN concentrators to the internet keeps practical risk elevated.

Root Cause

The root cause is improper validation of fragment values within incoming IKE packets. The parser assumes well-formed fragment structures and dereferences or copies data based on attacker-controlled fields. When an unexpected value bypasses internal bounds checks, the resulting heap operation corrupts memory and forces the process to terminate.

Attack Vector

An attacker sends a crafted IKE packet containing an unexpected fragment value to UDP port 500 on a vulnerable gateway. No credentials, prior session, or user interaction are required. Successful exploitation halts the VPN service, breaking active tunnels and preventing new connections until the service restarts. Refer to the Check Point Security Advisory sk184981 for vendor technical details.

Detection Methods for CVE-2026-48131

Indicators of Compromise

Unexpected termination or restart of the Check Point VPN daemon shortly after inbound UDP traffic on port 500
Spikes in malformed IKE fragments from a single source or distributed sources
Loss of VPN tunnel availability without corresponding administrative action
Crash logs or core dumps referencing the IKE parsing routines

Detection Strategies

Inspect IKE traffic on UDP port 500 for fragments with anomalous offsets, lengths, or fragment identifiers
Correlate gateway process crash events with inbound IKE packet captures
Alert on repeated VPN service restarts across short time windows

Monitoring Recommendations

Centralize gateway syslog and crash telemetry for real-time analysis
Monitor VPN availability metrics and trigger alerts when tunnel counts drop unexpectedly
Capture full packet traces on UDP port 500 during suspected disruption events for forensic review

How to Mitigate CVE-2026-48131

Immediate Actions Required

Apply the fix described in Check Point Security Advisory sk184981 to all affected gateways
Restrict UDP port 500 exposure to known VPN peers using upstream ACLs where feasible
Enable automatic service watchdog or high-availability failover to reduce downtime from crashes

Patch Information

Check Point has published remediation guidance in advisory sk184981. Administrators should consult the advisory for the specific hotfix or version that resolves the IKE fragment handling defect and apply it according to vendor-supplied upgrade procedures.

Workarounds

Limit inbound IKE traffic to the IP ranges of authorized VPN peers through perimeter firewall rules
Deploy redundant VPN gateways behind a load balancer to maintain availability during a crash
Where remote access is not required from the public internet, restrict UDP port 500 to trusted network segments

bash

# Example perimeter ACL restricting IKE to authorized peers (illustrative)
# Replace <peer_ip> entries with the actual VPN peer addresses
iptables -A INPUT -p udp --dport 500 -s <peer_ip_1> -j ACCEPT
iptables -A INPUT -p udp --dport 500 -s <peer_ip_2> -j ACCEPT
iptables -A INPUT -p udp --dport 500 -j DROP