CVE-2026-21765: HCL BigFix Insecure Permissions Vulnerability

CVE-2026-21765 Overview

HCL BigFix Platform is affected by insecure permissions on private cryptographic keys. The private cryptographic keys located on a Windows host machine might be subject to overly permissive file system permissions, potentially allowing unauthorized local users to access sensitive cryptographic material.

Critical Impact

Local attackers with low privileges can potentially access private cryptographic keys due to improper file system permissions, enabling credential theft, man-in-the-middle attacks, or impersonation of trusted systems within the BigFix infrastructure.

Affected Products

• HCL BigFix Platform (Windows installations)
• Systems storing BigFix private cryptographic keys
• Windows host machines running BigFix components

Discovery Timeline

• 2026-04-02 - CVE CVE-2026-21765 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-21765

Vulnerability Analysis

This vulnerability stems from CWE-276 (Incorrect Default Permissions), where the HCL BigFix Platform fails to properly restrict file system permissions on private cryptographic key files stored on Windows hosts. When cryptographic keys are deployed with overly permissive access controls, any local user on the system may be able to read these sensitive files.

Private cryptographic keys are foundational to the security model of endpoint management platforms like BigFix. These keys are used for signing actions, authenticating communications between components, and establishing trust within the managed environment. Unauthorized access to these keys could enable an attacker to forge signed commands, decrypt protected communications, or impersonate legitimate BigFix infrastructure components.

The attack requires local access to the affected Windows system but does not require administrative privileges, making it exploitable by any authenticated user on the machine. The scope is changed because compromising these keys could affect other systems within the BigFix deployment that trust the compromised cryptographic material.

Root Cause

The root cause of this vulnerability is the improper assignment of file system permissions during the installation or configuration of HCL BigFix Platform on Windows systems. When private cryptographic key files are created or stored, the platform does not adequately restrict access to these files, leaving them readable by users beyond those who require access for legitimate operational purposes.

This type of configuration flaw typically occurs when:

• Default installation routines do not properly configure Access Control Lists (ACLs) on sensitive directories
• Key files inherit overly permissive parent directory permissions
• Security hardening steps are not enforced during deployment

Attack Vector

The attack vector is local, requiring an attacker to have authenticated access to the Windows host where BigFix is installed. The exploitation path involves:

1. An attacker gains local user access to a Windows machine running HCL BigFix Platform
2. The attacker enumerates file system locations where BigFix stores cryptographic keys (typically in program data or installation directories)
3. Due to misconfigured permissions, the attacker can read the private key files
4. With access to private keys, the attacker can potentially sign malicious actions, decrypt communications, or impersonate trusted BigFix components

The vulnerability mechanism centers on improper file permission configuration. On Windows systems, private cryptographic keys should be protected with restrictive NTFS permissions that limit access to the SYSTEM account and specific service accounts. When these permissions are misconfigured, standard users can traverse to key storage locations and read sensitive cryptographic material. For detailed technical information, refer to the HCL Software Knowledge Base Article.

Detection Methods for CVE-2026-21765

Indicators of Compromise

• Unexpected file access events on BigFix cryptographic key storage directories
• Non-administrative users accessing files in BigFix installation or data directories
• Audit logs showing read operations on .key, .pem, or certificate files by unauthorized accounts
• Signs of key exfiltration such as unusual file copy operations or network transfers from key locations

Detection Strategies

• Enable Windows Security Auditing for object access on directories containing BigFix cryptographic keys
• Deploy file integrity monitoring (FIM) solutions to detect unauthorized access or modifications to key files
• Use PowerShell or security tools to audit current ACLs on BigFix key storage directories and alert on permissive configurations
• Monitor for anomalous authentication events that could indicate use of stolen cryptographic credentials

Monitoring Recommendations

• Configure SIEM rules to alert on file access events involving BigFix key files from non-service accounts
• Regularly audit file permissions on sensitive BigFix directories using automated compliance checks
• Implement endpoint detection to identify processes attempting to read cryptographic key files outside of normal BigFix operations
• Review Windows Event Logs for Security Event ID 4663 (object access attempts) targeting key storage paths

How to Mitigate CVE-2026-21765

Immediate Actions Required

• Audit file system permissions on all directories containing HCL BigFix private cryptographic keys
• Restrict ACLs on key files to allow access only by SYSTEM, local Administrators, and the BigFix service account
• Review recent access logs for any unauthorized access to key files and investigate potential compromise
• If unauthorized access is detected, consider rotating affected cryptographic keys

Patch Information

Refer to the official HCL Software Knowledge Base Article for vendor-provided remediation guidance and any available patches or updated installation packages that address the permission configuration issue.

Workarounds

• Manually configure restrictive NTFS permissions on BigFix key storage directories to remove access for standard users
• Implement the principle of least privilege by ensuring only necessary service accounts have read access to cryptographic materials
• Use Windows Group Policy to enforce secure default permissions on sensitive application directories
• Consider storing cryptographic keys in a Hardware Security Module (HSM) or Windows certificate store with proper access controls

# PowerShell example to audit and fix permissions on BigFix key directory
# Audit current permissions
Get-Acl "C:\Program Files (x86)\BigFix Enterprise\BES Server\KeyStorage" | Format-List

# Remove inherited permissions and restrict to SYSTEM and Administrators only
$path = "C:\Program Files (x86)\BigFix Enterprise\BES Server\KeyStorage"
$acl = Get-Acl $path
$acl.SetAccessRuleProtection($true, $false)
$adminRule = New-Object System.Security.AccessControl.FileSystemAccessRule("BUILTIN\Administrators","FullControl","ContainerInherit,ObjectInherit","None","Allow")
$systemRule = New-Object System.Security.AccessControl.FileSystemAccessRule("NT AUTHORITY\SYSTEM","FullControl","ContainerInherit,ObjectInherit","None","Allow")
$acl.AddAccessRule($adminRule)
$acl.AddAccessRule($systemRule)
Set-Acl $path $acl