CVE-2026-6891

Executive Summary

CVE-2026-6891 is a local privilege escalation vulnerability in Canon’s My Image Garden for macOS (versions 3.6.8 and earlier). The installer improperly handles symbolic links, allowing a local attacker with login privileges to exploit a crafted symlink during installation to modify permissions of files they would not normally have access to. This is a classic symlink race condition (CWE-61) that can lead to unauthorized file permission changes, potentially enabling further system compromise. The CVSS score is 5.0 (Medium), with a low attack complexity but requiring local access. No public exploit code or patch is currently available.

CVSS Breakdown & Threat Level

• CVSS Score: 5.0 (Medium)
• Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
• Attack Vector: Local (AV:L) – requires physical or SSH access to the macOS system.
• Attack Complexity: Low (AC:L) – no special conditions beyond a standard user session.
• Privileges Required: Low (PR:L) – attacker needs a standard user account.
• User Interaction: None (UI:N) – no victim action needed beyond the installer running.
• Scope: Unchanged (S:U) – the vulnerable component and the impacted resource are in the same security authority.
• Confidentiality Impact: None (C:N) – no direct data disclosure.
• Integrity Impact: High (I:H) – attacker can modify permissions of arbitrary files.
• Availability Impact: None (A:N) – no denial of service.

Threat Level: Medium. The vulnerability is local-only and requires an attacker to already have a foothold on the system. However, it can be chained with other exploits to escalate privileges or tamper with system files.

Deep Dive & Mechanics

The vulnerability lies in the installer of My Image Garden for macOS (versions ≤ 3.6.8). During installation, the installer creates or modifies files and directories. If the installer does not securely handle symbolic links (symlinks), a local attacker can pre-create a symlink pointing to a target file (e.g., a system configuration file or a protected resource) in a location where the installer will write. When the installer follows the symlink, it inadvertently changes permissions on the attacker-specified target file, granting the attacker elevated access.

Attack Flow:

1. Attacker gains low-privilege access to a macOS system.
2. Attacker identifies a directory where the My Image Garden installer will write files (e.g., /tmp, /Library/Application Support/Canon/).
3. Attacker creates a symbolic link in that directory pointing to a protected file (e.g., /etc/sudoers or a system binary).
4. The installer runs (either by the attacker or another user) and follows the symlink, modifying permissions on the target file.
5. Attacker now has unauthorized write access to the target file, enabling privilege escalation or system compromise.

Root Cause: The installer uses insecure file operations (e.g., chmod, chown, or file creation) without checking if the path is a symlink or using O_NOFOLLOW flags.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable pattern and the expected fix.

Vulnerable Code (Conceptual):

// Insecure: follows symlinks
chmod(path, 0777);

Patched Code (Expected):

// Secure: uses O_NOFOLLOW to avoid symlinks
int fd = open(path, O_NOFOLLOW | O_RDONLY);
if (fd == -1) {
    // handle error
}
fchmod(fd, 0777);
close(fd);

The patched version would use open() with O_NOFOLLOW to ensure the operation fails if the path is a symlink, or use lchmod() (if available) to change permissions on the symlink itself rather than its target.

Exploitation & Lab Setup

Red Team

Prerequisites:

• macOS system with My Image Garden ≤ 3.6.8 installed.
• Low-privilege user account (e.g., attacker).
• Target file to escalate privileges (e.g., /etc/sudoers).

Exploitation Steps:

1. Identify the installer’s temporary directory (e.g., /tmp/com.canon.MyImageGarden/).
2. Create a symlink:

   ln -s /etc/sudoers /tmp/com.canon.MyImageGarden/somefile
   

3. Trigger the installer (e.g., by running the app or waiting for a scheduled update).
4. After installation, verify permissions on /etc/sudoers:

   ls -la /etc/sudoers
   

5. If successful, the file will have world-writable permissions, allowing the attacker to modify it and grant themselves sudo access.

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

Blue Team

Detection:

• Monitor for symlink creation in directories used by Canon installers (e.g., /tmp/, /Library/Application Support/Canon/).
• Alert on unusual file permission changes on system files (e.g., /etc/sudoers, /etc/passwd).
• Use File Integrity Monitoring (FIM) to detect unauthorized modifications.

Prevention:

• Apply the principle of least privilege: restrict write access to installation directories.
• Use macOS security features like System Integrity Protection (SIP) to protect critical files.
• Deploy endpoint detection and response (EDR) rules to block symlink attacks.

Indicators of Compromise (IOCs)

• File System Artifacts:
  • Unexpected symlinks in /tmp/ or /Library/Application Support/Canon/ pointing to system files.
  • Modified permissions on /etc/sudoers, /etc/passwd, or other protected files.
• Process Artifacts:
  • The My Image Garden installer process (MyImageGardenInstaller) running with unusual file operations.
• Log Artifacts:
  • macOS unified logs showing chmod or chown operations on symlinked paths.
  • Security audit logs (e.g., log show --predicate 'eventMessage contains "symlink"').

Detection Engineering

YARA Rule

rule CVE_2026_6891_Symlink_Exploit {
    meta:
        description = "Detects symlink creation targeting system files for CVE-2026-6891"
        author = "Valters IT"
        date = "2025-04-10"
        hash = "d41d8cd98f00b204e9800998ecf8427e"
    strings:
        $symlink_cmd = "ln -s" ascii nocase
        $target_system = "/etc/sudoers" ascii nocase
        $target_passwd = "/etc/passwd" ascii nocase
        $canon_dir = "/Library/Application Support/Canon" ascii nocase
    condition:
        any of ($symlink_cmd) and any of ($target_system, $target_passwd) and $canon_dir
}

Sigma Rule

title: Canon My Image Garden Symlink Exploit
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects symlink creation targeting system files during Canon installer execution
author: Valters IT
date: 2025-04-10
logsource:
    category: process_creation
    product: macos
detection:
    selection:
        Image|endswith: '/ln'
        CommandLine|contains: '-s'
        CommandLine|contains:
            - '/etc/sudoers'
            - '/etc/passwd'
            - '/etc/ssh/sshd_config'
    condition: selection
falsepositives:
    - Legitimate system administration
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-6891 Canon My Image Garden Symlink Exploit"; flow:to_server,established; content:"ln -s"; nocase; content:"/etc/sudoers"; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable or uninstall My Image Garden version 3.6.8 or earlier until a patch is released.
2. Restrict write access to installation directories using macOS permissions.
3. Enable System Integrity Protection (SIP) to protect critical system files.

Long-term Fix:

• Canon must release a patched version that uses secure file operations (e.g., O_NOFOLLOW).
• Users should apply the patch as soon as it becomes available.

Workarounds:

• Use a non-privileged user account for installation.
• Monitor for suspicious symlink creation using the provided detection rules.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert