CVE-2023-6336

Executive Summary

CVE-2023-6336 is a high-severity local privilege escalation vulnerability affecting HYPR Workforce Access on macOS. The flaw is classified as an Improper Link Resolution Before File Access ('Link Following') vulnerability (CWE-59). An authenticated local attacker can exploit a symbolic link (symlink) to manipulate file access, potentially leading to arbitrary file read, write, or deletion with the privileges of the HYPR process. This could allow an attacker to escalate privileges, exfiltrate sensitive data, or disrupt system operations. The vulnerability is present in versions prior to 8.7. No public proof-of-concept (PoC) or exploit code has been released at this time.

CVSS Breakdown & Threat Level

• CVSS Score: 7.2 (High)
• Attack Vector (AV): Local (L) – The attacker must have local access to the system.
• Attack Complexity (AC): Low (L) – No special conditions are required beyond standard user access.
• Privileges Required (PR): Low (L) – The attacker needs a standard user account.
• User Interaction (UI): None (N) – No user action is required for exploitation.
• Scope (S): Unchanged (U) – The vulnerability does not cross a trust boundary.
• Confidentiality (C): High (H) – Sensitive data could be read.
• Integrity (I): High (H) – Files could be modified or deleted.
• Availability (A): High (H) – System availability could be impacted.

Threat Level: High. While the EPSS score is currently 0.0%, the local attack vector and high impact make this a significant risk for enterprise environments using HYPR Workforce Access.

Deep Dive & Mechanics

The vulnerability resides in how HYPR Workforce Access handles file operations on macOS. The application fails to properly validate symbolic links before performing file access operations. A local attacker can create a malicious symlink pointing to a sensitive file (e.g., /etc/passwd, /private/etc/sudoers, or user data). When the HYPR process (running with elevated privileges) follows this symlink, it performs the file operation on the target file instead of the intended location.

Attack Scenario:

1. An attacker with a standard user account on a macOS system identifies a file operation performed by the HYPR process (e.g., writing a log file, reading a configuration file).
2. The attacker creates a symbolic link from the expected file path to a sensitive target file (e.g., ln -s /etc/sudoers /tmp/hypr_log).
3. When the HYPR process performs the file operation, it follows the symlink and writes to or reads from the target file.
4. This can lead to privilege escalation (e.g., overwriting sudoers), data exfiltration, or denial of service.

Vulnerable vs. Patched Code

Vulnerable Code (Pre-8.7): The application likely uses standard file I/O functions (e.g., fopen, open, write) without checking if the path is a symbolic link. Example (pseudocode):

FILE *fp = fopen("/tmp/hypr_log", "w");
if (fp) {
    fprintf(fp, "log data");
    fclose(fp);
}

Patched Code (8.7+): The patched version uses secure file operations that resolve symlinks before access, or uses O_NOFOLLOW flag to prevent following symlinks. Example (pseudocode):

int fd = open("/tmp/hypr_log", O_WRONLY | O_CREAT | O_NOFOLLOW, 0644);
if (fd != -1) {
    write(fd, "log data", 8);
    close(fd);
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to a macOS system running HYPR Workforce Access < 8.7.
• A standard user account.

Steps:

1. Identify a file path that the HYPR process writes to or reads from (e.g., /tmp/hypr_log).
2. Create a symbolic link from that path to a target file:

   ln -sf /etc/sudoers /tmp/hypr_log
   

3. Trigger the HYPR process to perform the file operation (e.g., by restarting the service or performing a specific action).
4. Verify the impact (e.g., check if sudoers was overwritten).

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

Blue Team (Detection & Prevention)

Detection:

• Monitor for creation of symbolic links in directories used by HYPR (e.g., /tmp, /var/tmp).
• Use file integrity monitoring (FIM) to detect unauthorized changes to sensitive files.
• Enable macOS security features like System Integrity Protection (SIP) and sandboxing.

Prevention:

• Upgrade to HYPR Workforce Access 8.7 or later.
• Restrict write access to directories where HYPR performs file operations.
• Use endpoint detection and response (EDR) tools to monitor for symlink attacks.

Indicators of Compromise (IOCs)

• File Paths:
  • /tmp/hypr_* (or similar temporary files)
  • /var/tmp/hypr_*
• Process Names:
  • HYPR Workforce Access (or related daemon)
• Registry/System Changes:
  • Unexpected symbolic links in /tmp/ or /var/tmp/ pointing to sensitive files.
• Network Connections:
  • No specific network IOCs; this is a local attack.

Detection Engineering

YARA Rule

rule CVE_2023_6336_Symlink_Attack {
    meta:
        description = "Detects symbolic link creation targeting HYPR Workforce Access"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-6336"
    strings:
        $symlink_cmd = "ln -sf" ascii wide nocase
        $hypr_path = "/tmp/hypr" ascii wide nocase
        $sensitive_file = "/etc/sudoers" ascii wide nocase
    condition:
        $symlink_cmd and $hypr_path and $sensitive_file
}

Sigma Rule

title: CVE-2023-6336 - HYPR Symlink Attack
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects creation of symbolic links targeting HYPR Workforce Access
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2023-6336
logsource:
    category: process_creation
    product: macos
detection:
    selection:
        Image|endswith: '/ln'
        CommandLine|contains|all:
            - '-sf'
            - '/tmp/hypr'
            - '/etc/sudoers'
    condition: selection
falsepositives:
    - Legitimate administrative actions
level: high

Suricata Rule

alert ip any any -> any any (msg:"CVE-2023-6336 - HYPR Symlink Attack"; content:"ln -sf"; content:"/tmp/hypr"; content:"/etc/sudoers"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade to HYPR Workforce Access version 8.7 or later.
2. Restrict write access to directories used by HYPR (e.g., /tmp, /var/tmp) for non-privileged users.
3. Enable macOS System Integrity Protection (SIP) to protect system files.

Long-term Measures:

• Implement file integrity monitoring (FIM) for critical system files.
• Use endpoint detection and response (EDR) solutions to detect symlink attacks.
• Conduct regular security audits of third-party applications.

Workarounds (if patching is not immediately possible):

• Remove write permissions for standard users on directories where HYPR writes files.
• Use macOS sandboxing to restrict HYPR's file system access.

Valters IT
Securing Digital Frontiers