CVE-2026-6892

Executive Summary

CVE-2026-6892 is a local privilege escalation vulnerability in the Canon CUPS Printer Driver installer for macOS. The installer improperly handles symbolic links during the installation process, allowing a local attacker with login privileges to create a specially crafted symbolic link. When the installer runs, it follows the symlink and modifies directory permissions, granting the attacker write access to directories they would not normally control. This can lead to further system compromise, such as planting malicious executables or modifying system files. The vulnerability affects specific Canon printer driver versions for the PIXUS iX6800 Series (Japan) and PIXMA MG2500/iX6800 Series (US and Europe). No public exploit code or patch is currently available.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Local (L) – The attacker must have local access to the macOS system.
• Attack Complexity (AC): Low (L) – No special conditions are required beyond standard user privileges.
• Privileges Required (PR): Low (L) – The attacker needs only login-level privileges.
• User Interaction (UI): None (N) – The exploit does not require any action from another user.
• Scope (S): Unchanged (U) – The vulnerability does not cross trust boundaries.
• Confidentiality (C): None (N) – No direct data exposure.
• Integrity (I): High (H) – The attacker can modify directory permissions, potentially leading to file replacement or system tampering.
• Availability (A): None (N) – No direct denial of service.

CVSS Score: 5.0 (Medium) – The local attack vector and low privileges required make this a realistic threat for multi-user macOS environments or shared workstations.

Deep Dive & Mechanics

The vulnerability resides in the installer script of the Canon CUPS Printer Driver for macOS. During installation, the installer performs file operations (e.g., creating directories, copying files) without properly validating symbolic links. A local attacker can pre-create a symbolic link in a location that the installer will access (e.g., /tmp, /Library/Printers, or a user-writable staging directory). When the installer follows the symlink, it applies permission changes to the target directory instead of the intended location.

For example, if the installer intends to set permissions on /Library/Printers/Canon but the attacker has placed a symlink at that path pointing to /etc, the installer will modify permissions on /etc, granting the attacker write access to system configuration files. This can be leveraged to install a persistent backdoor, modify launch daemons, or escalate privileges to root.

The vulnerability is specific to the installer binary or script, not the printer driver itself. The affected versions are:

• Japan: Canon PIXUS iX6800 Series CUPS Printer Driver for macOS Version 16.91.0.0 or earlier
• US/Europe: Canon PIXMA MG2500 Series and iX6800 Series CUPS Printer Driver for macOS Version 16.91.0.0 or earlier

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code is likely in a shell script or a compiled binary that performs file operations without using secure file operations (e.g., O_NOFOLLOW or lstat checks). A hypothetical patch would involve:

• Using lstat() instead of stat() to detect symbolic links before performing permission changes.
• Using open() with O_NOFOLLOW flag to prevent following symlinks.
• Validating that the target path is within expected directories (e.g., /Library/Printers).

Vulnerable pseudo-code:

# Vulnerable installer script
chmod 755 /Library/Printers/Canon
chown root:admin /Library/Printers/Canon

Patched pseudo-code:

# Patched installer script
if [ -L "/Library/Printers/Canon" ]; then
    echo "Error: Symlink detected, aborting."
    exit 1
fi
chmod 755 /Library/Printers/Canon
chown root:admin /Library/Printers/Canon

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• Local user account on macOS (e.g., testuser)
• Canon CUPS Printer Driver installer (vulnerable version)
• Ability to write to a directory that the installer accesses (e.g., /tmp or /Library/Printers)

Steps:

1. Identify the target directory the installer will modify (e.g., /Library/Printers/Canon).
2. Create a symbolic link from that path to a sensitive directory (e.g., /etc):

   ln -s /etc /Library/Printers/Canon
   

3. Run the Canon printer driver installer as the local user (or via sudo if required).
4. After installation, verify that /etc permissions have been changed (e.g., world-writable):

   ls -ld /etc
   

5. Exploit the modified permissions to write a malicious file (e.g., a cron job or launch daemon):

   echo "0 * * * * root /tmp/backdoor.sh" > /etc/crontab
   

Expected Outcome: The attacker gains write access to /etc, allowing privilege escalation or persistence.

Blue Team (Detection & Defense)

Detection:

• Monitor for creation of symbolic links in printer-related directories (/Library/Printers, /tmp).
• Alert on permission changes to sensitive system directories (/etc, /usr, /bin).
• Use file integrity monitoring (FIM) to detect unauthorized modifications to /etc or /Library/Printers.

Defense:

• Restrict write access to /Library/Printers to only the _lp user or root.
• Use macOS security tools like sandbox-exec to sandbox the installer.
• Apply the principle of least privilege: do not run installers as root unless necessary.
• Monitor for unusual symlink creation using auditd or fs_usage.

Indicators of Compromise (IOCs)

• File System:

  • Unexpected symbolic links in /Library/Printers/ or /tmp/ pointing to system directories.
  • Modified permissions on /etc, /usr, or /bin (e.g., world-writable).
  • New files in /etc/crontab, /Library/LaunchDaemons/, or /Library/StartupItems/.

• Process:

  • Execution of the Canon installer binary (Canon CUPS Printer Driver Installer.app) by a non-admin user.
  • Unusual chmod or chown operations on system directories.

• Network:

  • No network indicators expected (local vulnerability).

Detection Engineering

YARA Rule

rule CVE_2026_6892_Canon_Printer_Symlink {
    meta:
        description = "Detects Canon printer installer files vulnerable to symlink attack"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2026-6892"
    strings:
        $installer_name = "Canon CUPS Printer Driver Installer"
        $vuln_version = "16.91.0.0"
        $symlink_path = "/Library/Printers/Canon"
    condition:
        $installer_name and $vuln_version and $symlink_path
}

Sigma Rule

title: Canon Printer Driver Symlink Privilege Escalation
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects creation of symbolic links in printer directories followed by permission changes to system directories
author: Valters IT
date: 2025-04-10
logsource:
    category: file_event
    product: macos
detection:
    selection:
        EventID: 2  # File creation
        TargetFilename|contains: '/Library/Printers/'
        TargetFilename|endswith: '.symlink' or '->'
    condition: selection
falsepositives:
    - Legitimate printer driver installation
level: high

Suricata Rule

alert file any any -> any any (msg:"CVE-2026-6892 Canon Printer Symlink Attack"; file.name:"/Library/Printers/Canon"; file.magic:"symbolic link"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Do not install the affected Canon printer driver versions (16.91.0.0 or earlier) on shared or multi-user macOS systems.
2. Remove the vulnerable driver if already installed:

   sudo lpadmin -x "Canon_PIXUS_iX6800_Series"
   sudo rm -rf /Library/Printers/Canon
   

3. Monitor for unauthorized symlink creation in /Library/Printers/ and /tmp/.

Long-term Fix:

• Canon must release a patched installer that validates symlinks using lstat() and O_NOFOLLOW.
• Until a patch is available, use alternative printer drivers or restrict installer execution to admin users only.

Workaround:

• Run the installer in a sandboxed environment (e.g., using sandbox-exec with a restrictive profile).
• Manually verify that no symlinks exist in the target directories before installation:

  find /Library/Printers -type l -exec rm {} \;
  

Valters IT