CVE-2026-20757

Executive Summary

CVE-2026-20757 is a low-severity (CVSS 2.5) improper locking vulnerability (CWE-667) affecting Gallagher’s Command Centre Server when integrated with the Gallagher Morpho integration. A privileged operator can exploit this flaw to cause a limited denial-of-service (DoS) condition, impacting system availability. The vulnerability exists in multiple versions of the Command Centre Server, including all versions 9.00 and prior, as well as specific builds of 9.10, 9.20, 9.30, and 9.40. No public proof-of-concept (PoC) or exploit code is available, and the EPSS score is 0.0%, indicating a very low probability of exploitation in the wild. The vendor has released patches for all affected versions.

Supply Chain & Package Security

This vulnerability is not related to an open-source package manager (NPM, PyPI, Go, Ruby). It affects a proprietary physical security and access control system from Gallagher. The supply chain risk is limited to the integrity of the Gallagher software distribution channels.

CVSS Breakdown & Threat Level

• CVSS Score: 2.5 (Low)
• Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L
• Attack Vector (AV): Local (L) – The attacker must have local access to the Command Centre Server.
• Attack Complexity (AC): Low (L) – No special conditions are required to exploit.
• Privileges Required (PR): High (H) – The attacker must be a privileged operator.
• User Interaction (UI): None (N) – No user interaction is required.
• Scope (S): Unchanged (U) – The vulnerability does not affect other components.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): Low (L) – Limited denial-of-service.

Threat Level: Low. The requirement for high privileges and local access significantly reduces the attack surface. The impact is limited to a partial DoS.

Deep Dive & Mechanics

The vulnerability is rooted in an improper locking mechanism (CWE-667) within the Gallagher Morpho integration component of the Command Centre Server. The Morpho integration is used for biometric (fingerprint) authentication. When a privileged operator performs a specific sequence of operations, the locking mechanism fails to properly synchronize access to a shared resource. This can lead to a race condition or deadlock, causing the Command Centre Server to become unresponsive or crash, resulting in a denial-of-service condition.

The flaw is triggered by a privileged operator, meaning an attacker who already has administrative-level access to the system. This could be a malicious insider or an external attacker who has compromised a high-privilege account. The DoS is limited, likely affecting only the Morpho integration functionality or a specific subsystem, rather than the entire server.

Vulnerable vs. Patched Code

No specific code snippets are available for this vulnerability. However, the patch addresses the improper locking by implementing proper mutex or semaphore synchronization in the Morpho integration module. The vulnerable code likely had a missing or incorrect lock acquisition/release pattern, while the patched code ensures atomic operations on shared resources.

Vulnerable (Conceptual):

// Vulnerable: Missing lock before accessing shared resource
void process_morpho_request(request_t *req) {
    // No lock acquired
    shared_resource->data = req->input;
    // Race condition possible
    process_data(shared_resource);
    // No lock released
}

Patched (Conceptual):

// Patched: Proper locking
void process_morpho_request(request_t *req) {
    mutex_lock(&shared_resource_lock);
    shared_resource->data = req->input;
    process_data(shared_resource);
    mutex_unlock(&shared_resource_lock);
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to a Gallagher Command Centre Server with a vulnerable version (e.g., 9.10 prior to vEL9.10.4647).
• A privileged operator account (e.g., administrator or security manager).

Exploitation Steps:

1. Log in to the Command Centre Server with the privileged operator account.
2. Navigate to the Morpho integration settings.
3. Perform a series of rapid, concurrent operations on the biometric enrollment or verification functions. For example, simultaneously trigger multiple enrollment requests or repeatedly toggle the integration service.
4. The improper locking will cause a race condition, leading to a deadlock or crash of the Morpho integration service.
5. Verify the DoS by observing that biometric authentication fails or the Command Centre Server becomes unresponsive for the affected functionality.

Note: No public exploit code is available. This is a conceptual approach.

Blue Team

Detection:

• Monitor for unusual patterns of privileged operator activity, especially rapid or concurrent operations on the Morpho integration.
• Look for error logs indicating deadlocks or timeouts in the Morpho integration module.
• Use the Sigma rule provided in the Detection Engineering section.

Mitigation:

• Apply the vendor patch immediately.
• Restrict privileged operator accounts to only necessary personnel.
• Implement additional logging and alerting for administrative actions.

Indicators of Compromise (IOCs)

• Log Entries: Repeated error messages related to "Morpho integration", "lock timeout", or "deadlock detected" in the Command Centre Server logs.
• System Behavior: Intermittent unavailability of biometric authentication functions.
• Process Anomalies: The Gallagher.CommandCentre.Server.exe process (or equivalent) may show high CPU usage or become unresponsive.

Detection Engineering

YARA Rule

rule CVE_2026_20757_Morpho_Lock {
    meta:
        description = "Detects potential exploitation of CVE-2026-20757 via log patterns"
        author = "Valters IT"
        date = "2025-04-17"
        reference = "CVE-2026-20757"
    strings:
        $log1 = "Morpho integration" nocase
        $log2 = "lock timeout" nocase
        $log3 = "deadlock" nocase
        $log4 = "improper locking" nocase
    condition:
        any of ($log*) and #log1 > 5
}

Sigma Rule

title: CVE-2026-20757 - Gallagher Morpho Integration DoS
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects signs of exploitation of CVE-2026-20757 in Gallagher Command Centre Server logs.
author: Valters IT
date: 2025-04-17
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-20757
logsource:
    product: gallagher
    service: command_centre_server
detection:
    selection:
        EventID: 1000-2000  # Example event IDs for errors
        Message|contains:
            - 'Morpho integration'
            - 'lock timeout'
            - 'deadlock'
            - 'improper locking'
    condition: selection
falsepositives:
    - Legitimate administrative actions during maintenance
level: medium

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-20757 - Gallagher Morpho Integration DoS Attempt"; flow:to_server,established; content:"Morpho integration"; nocase; content:"lock timeout"; nocase; within:100; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade the Command Centre Server to the following patched versions or later:
   • vEL9.40.1976 (MR1)
   • vEL9.30.3382 (MR4)
   • vEL9.20.3783 (MR6)
   • vEL9.10.4647 (MR9)
2. Workaround: If patching is not immediately possible, restrict access to the Morpho integration settings to only essential personnel and monitor for unusual activity.

Long-Term Measures:

• Implement the principle of least privilege for all operator accounts.
• Enable comprehensive logging and auditing of all administrative actions.
• Regularly review and update access control policies.

Valters IT
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