CVE-2025-27829

Executive Summary

CVE-2025-27829 is a denial-of-service (DoS) vulnerability affecting Stormshield Network Security (SNS) version 4.3.x prior to 4.3.35. The issue arises when multicast streams are enabled on different interfaces, potentially allowing an attacker to interrupt multicast traffic on some interfaces. This can lead to a denial of the multicast routing service on the firewall, impacting network availability. No public proof-of-concept (PoC) or exploit code has been released, and the CVSS score is currently unassigned. The vendor has released a patch in version 4.3.35.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unassigned)
• Attack Vector (AV): Network (likely)
• Attack Complexity (AC): Low (likely)
• Privileges Required (PR): None (likely)
• User Interaction (UI): None (likely)
• Scope (S): Unchanged (likely)
• Confidentiality (C): None
• Integrity (I): None
• Availability (A): High
• Threat Level: Medium (due to potential for service disruption, but no known active exploitation)

Deep Dive & Mechanics

The vulnerability resides in the multicast routing service of Stormshield SNS. When multicast streams are enabled on multiple interfaces, a race condition or resource exhaustion issue can occur. Specifically, the service may mishandle multicast group membership or forwarding state when streams are active on different interfaces. An attacker can exploit this by sending crafted multicast traffic or by manipulating multicast group memberships to cause the service to drop or misroute multicast packets on certain interfaces. This results in a denial of service for multicast traffic, impacting applications relying on multicast (e.g., video streaming, real-time data distribution).

The root cause is likely improper synchronization or resource management in the multicast routing code, leading to a state where the service cannot properly forward multicast packets across all enabled interfaces.

Vulnerable vs. Patched Code

No specific code diff is publicly available. However, the patch in SNS 4.3.35 likely addresses the race condition or resource exhaustion by:

• Improving synchronization when handling multicast group membership changes.
• Adding proper error handling for multicast stream state transitions.
• Limiting resource allocation per interface to prevent exhaustion.

Vulnerable Code (Conceptual):

// Pseudocode for vulnerable multicast handler
void handle_multicast_stream(interface_t *iface, packet_t *pkt) {
    // No locking when updating multicast state across interfaces
    if (multicast_state[iface->id] == ACTIVE) {
        forward_packet(pkt);
    }
    // Race condition: state may change concurrently
}

Patched Code (Conceptual):

// Pseudocode for patched multicast handler
void handle_multicast_stream(interface_t *iface, packet_t *pkt) {
    mutex_lock(&multicast_lock);
    if (multicast_state[iface->id] == ACTIVE) {
        forward_packet(pkt);
    }
    mutex_unlock(&multicast_lock);
}

Exploitation & Lab Setup

Red Team

1. Setup: Deploy Stormshield SNS 4.3.34 in a lab environment with at least two network interfaces (e.g., eth0, eth1). Enable multicast routing on both interfaces.
2. Trigger: Send continuous multicast traffic (e.g., using iperf or mcjoin) to both interfaces simultaneously. Use a script to rapidly join and leave multicast groups on different interfaces.
3. Exploit: The vulnerability may be triggered by sending a high rate of IGMP membership reports or by causing a race condition in the multicast state machine. Example using scapy:

   from scapy.all import *
   import threading
   
   def send_igmp(iface):
       pkt = IP(dst="224.0.0.1")/IGMP(type=0x16, gaddr="239.1.1.1")
       send(pkt, iface=iface, loop=1, inter=0.01)
   
   t1 = threading.Thread(target=send_igmp, args=("eth0",))
   t2 = threading.Thread(target=send_igmp, args=("eth1",))
   t1.start()
   t2.start()
   

4. Impact: Multicast traffic on one or both interfaces will be disrupted, causing denial of service for multicast-dependent applications.

Blue Team

1. Detection: Monitor for unusual IGMP traffic patterns, especially high rates of membership reports or leaves from the same source.
2. Logging: Enable detailed logging on the firewall for multicast events. Look for errors like "multicast routing service failure" or "interface multicast state mismatch".
3. Mitigation: If patching is not immediately possible, consider disabling multicast on non-essential interfaces or implementing rate limiting for IGMP traffic.
4. Forensics: Collect packet captures on affected interfaces to identify the source of multicast disruption. Analyze firewall logs for timestamps of service degradation.

Indicators of Compromise (IOCs)

• Network: Unusual IGMP traffic patterns (high rate of join/leave messages).
• Logs: Firewall logs showing "multicast routing service error" or "interface multicast state inconsistency".
• System: Degraded performance for multicast applications (e.g., video streaming, real-time data).
• File: No specific file-based IOCs.

Detection Engineering

YARA Rule

rule CVE_2025_27829_Multicast_DoS {
    meta:
        description = "Detects potential exploitation of CVE-2025-27829 via IGMP traffic patterns"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-27829"
    strings:
        $igmp_join = { 16 00 00 00 }  // IGMPv2 membership report
        $igmp_leave = { 17 00 00 00 } // IGMPv2 leave group
    condition:
        #igmp_join > 100 or #igmp_leave > 100
}

Sigma Rule

title: CVE-2025-27829 Multicast DoS Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects high rate of IGMP messages indicating potential exploitation
author: Valters IT
logsource:
    category: firewall
    product: stormshield
detection:
    selection:
        event: "multicast routing error"
    condition: selection
falsepositives:
    - Legitimate multicast applications
level: medium

Suricata Rule

alert udp any any -> any any (msg:"CVE-2025-27829 Multicast DoS Attempt"; content:"|16 00 00 00|"; threshold: type both, track by_src, count 100, seconds 1; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Upgrade Stormshield SNS to version 4.3.35 or later.
2. Workaround: If patching is delayed, disable multicast on non-essential interfaces or apply ACLs to limit IGMP traffic.
3. Monitoring: Enable logging for multicast events and monitor for anomalies.
4. Network Segmentation: Isolate multicast traffic to trusted network segments.

Valters IT
Securing Digital Frontiers