CVE-2026-9261

Executive Summary

CVE-2026-9261 is a vulnerability in the Canon EOS Network Setting Tool version 1.5.0 and earlier, involving the use of weak SSH cryptographic algorithms. This flaw allows an unauthenticated, network-adjacent attacker to potentially decrypt or intercept SSH communications, leading to unauthorized access to sensitive configuration data or network credentials. The vulnerability has a CVSS score of 6.8 (Medium), with an EPSS score of 0.0%, indicating low exploitation likelihood at this time. No public proof-of-concept (PoC) or exploit code is available, and no patch has been released by Canon. The weakness stems from the use of deprecated or weak SSH ciphers (e.g., arcfour, CBC mode ciphers, or weak MAC algorithms) that are susceptible to cryptographic attacks such as plaintext recovery or man-in-the-middle (MITM) decryption.

CVSS Breakdown & Threat Level

• CVSS Score: 6.8 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
• Attack Vector: Network (AV:N) – exploitable remotely over the network.
• Attack Complexity: Low (AC:L) – no special conditions required.
• Privileges Required: None (PR:N) – no authentication needed.
• User Interaction: None (UI:N) – no user action required.
• Scope: Unchanged (S:U) – impact confined to the vulnerable component.
• Confidentiality Impact: High (C:H) – potential full disclosure of SSH session data.
• Integrity Impact: None (I:N) – no data modification.
• Availability Impact: None (A:N) – no denial of service.
• Threat Level: Medium – due to low EPSS and no public exploit, but high impact if exploited.

Deep Dive & Mechanics

The Canon EOS Network Setting Tool uses SSH for secure communication between the tool and the camera or network device. In version 1.5.0 and earlier, the SSH implementation is configured to accept weak cryptographic algorithms, including:

• Ciphers: arcfour (RC4), CBC mode ciphers (e.g., aes128-cbc, 3des-cbc)
• MAC algorithms: hmac-md5, hmac-sha1-96
• Key exchange algorithms: diffie-hellman-group1-sha1, diffie-hellman-group-exchange-sha1

These algorithms are considered weak because:

• RC4 (arcfour): Known biases allow plaintext recovery after capturing enough ciphertext.
• CBC mode ciphers: Vulnerable to padding oracle attacks and plaintext recovery if the SSH protocol is not properly implemented.
• Weak MACs: hmac-md5 and truncated MACs (hmac-sha1-96) reduce collision resistance, enabling potential forgery.
• Weak key exchange: diffie-hellman-group1-sha1 uses a 768-bit prime, which is susceptible to discrete logarithm attacks by well-resourced adversaries.

An attacker positioned on the network path (MITM) can force the SSH handshake to downgrade to these weak algorithms, then decrypt the session traffic, revealing credentials, configuration data, or other sensitive information transmitted over the SSH connection.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the SSH configuration in the Canon EOS Network Setting Tool. A patched version would enforce strong algorithms only.

Vulnerable configuration (conceptual):

# Example of weak SSH configuration in the tool
ssh_config = {
    'ciphers': ['arcfour', 'aes128-cbc', '3des-cbc'],
    'macs': ['hmac-md5', 'hmac-sha1-96'],
    'kex': ['diffie-hellman-group1-sha1', 'diffie-hellman-group-exchange-sha1']
}

Patched configuration (conceptual):

# Example of strong SSH configuration
ssh_config = {
    'ciphers': ['chacha20-poly1305@openssh.com', 'aes256-gcm@openssh.com'],
    'macs': ['hmac-sha2-256', 'hmac-sha2-512'],
    'kex': ['curve25519-sha256', 'diffie-hellman-group16-sha512']
}

Exploitation & Lab Setup

Red Team

Lab Setup:

• Target: Canon EOS Network Setting Tool v1.5.0 running on a Windows or macOS system.
• Attacker: Kali Linux with ssh-audit and mitmproxy or bettercap.
• Network: Same subnet or MITM position (e.g., ARP spoofing).

Exploitation Steps:

1. Scan for weak algorithms:

   ssh-audit <target_ip>
   

   Look for weak ciphers like arcfour or aes128-cbc.

2. Perform MITM attack: Use bettercap to ARP spoof the target and intercept SSH traffic.

   sudo bettercap -eval "set arp.spoof.targets <target_ip>; arp.spoof on; net.sniff on"
   

3. Downgrade SSH connection: Use a custom SSH proxy (e.g., ssh-mitm) to force weak algorithms.

   ssh-mitm --remote-host <target_ip> --remote-port 22 --local-port 2222
   

4. Capture and decrypt traffic: Use Wireshark to capture the SSH session and decrypt using known weak keys (if key exchange is compromised).

Blue Team

Detection:

• Monitor for SSH connections using weak ciphers (e.g., arcfour, aes128-cbc).
• Alert on SSH handshake downgrade attempts.
• Use network intrusion detection systems (NIDS) to flag weak SSH algorithm negotiation.

Hunting:

• Search logs for SSH connections with kex_algorithms containing diffie-hellman-group1-sha1.
• Check for repeated SSH handshake failures that may indicate downgrade attacks.

Mitigation:

• Isolate the Canon EOS Network Setting Tool on a separate VLAN with strict access controls.
• Use a VPN or SSH bastion host that enforces strong algorithms.
• Monitor for unauthorized SSH connections to the tool.

Indicators of Compromise (IOCs)

• Network IOCs:
  • SSH handshake containing arcfour, aes128-cbc, 3des-cbc in cipher list.
  • SSH key exchange using diffie-hellman-group1-sha1 or diffie-hellman-group-exchange-sha1.
  • Unusual SSH traffic from unexpected IPs on port 22.
• Host IOCs:
  • Presence of ssh-audit or ssh-mitm tools on the network.
  • ARP spoofing alerts on the local network.
• File IOCs:
  • Modified SSH configuration files (e.g., ssh_config or sshd_config) enabling weak algorithms.

Detection Engineering

YARA Rule

rule detect_weak_ssh_ciphers_canon_eos {
    meta:
        description = "Detects weak SSH cipher usage in Canon EOS Network Setting Tool traffic"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-9261"
    strings:
        $cipher_arcfour = "arcfour" ascii wide nocase
        $cipher_cbc = "aes128-cbc" ascii wide nocase
        $cipher_3des = "3des-cbc" ascii wide nocase
        $mac_md5 = "hmac-md5" ascii wide nocase
        $kex_weak = "diffie-hellman-group1-sha1" ascii wide nocase
    condition:
        any of ($cipher_*) or any of ($mac_*) or any of ($kex_*)
}

Sigma Rule

title: Weak SSH Cipher Negotiation Detected
id: 8a9b3c2d-1e5f-4a7b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects SSH handshake using weak cryptographic algorithms associated with CVE-2026-9261
author: Valters IT
date: 2025-04-10
logsource:
    category: network_connection
    product: zeek
detection:
    selection:
        service: ssh
        cipher_algorithm|contains:
            - 'arcfour'
            - 'aes128-cbc'
            - '3des-cbc'
        mac_algorithm|contains:
            - 'hmac-md5'
            - 'hmac-sha1-96'
        kex_algorithm|contains:
            - 'diffie-hellman-group1-sha1'
            - 'diffie-hellman-group-exchange-sha1'
    condition: selection
falsepositives:
    - Legitimate use of weak algorithms in isolated environments
level: high
tags:
    - attack.t1190
    - cve.2026.9261

Suricata Rule

alert tcp any any -> any 22 (msg:"CVE-2026-9261 - Weak SSH Cipher Negotiation"; flow:to_server,established; content:"|00 00 00 0c|ssh-rsa"; content:"arcfour"; distance:0; within:100; sid:1000001; rev:1;)

Remediation & Mitigation

• Immediate Actions:
  • Disable the Canon EOS Network Setting Tool if not in use.
  • Restrict network access to the tool using firewall rules (allow only trusted IPs).
  • Use a VPN or SSH bastion host that enforces strong cryptographic algorithms.
• Long-term Fix:
  • Await an official patch from Canon that updates the SSH library to disable weak algorithms.
  • If possible, manually update the SSH configuration file (e.g., ssh_config) to remove weak ciphers, MACs, and key exchange algorithms.
• Workaround:
  • Replace the SSH implementation with a hardened version (e.g., using OpenSSH with strong defaults).
  • Monitor for any SSH connections to the tool and alert on weak algorithm usage.

Valters IT
Securing digital frontiers, one vulnerability at a time.