CVE-2026-102489: Zammad Session Fixation Leading to RCE

Overview

CVE-2026-102489 describes a session fixation vulnerability affecting Zammad, an open-source help desk system. Successful exploitation allows an attacker to hijack a user’s session, which can then be escalated to remote code execution (RCE) with the privileges of the zammad user. This vulnerability is critical due to the potential for full system compromise and data exfiltration.

Technical Analysis

This vulnerability is a session fixation flaw, meaning an attacker can force a user’s session ID to a known value. Once the legitimate user authenticates with this fixed session ID, the attacker can then use the same ID to impersonate the user and gain access to their session. The NVD record specifies that this session hijack can lead to remote code execution as the zammad user.

• Affected Versions: Zammad versions 6.3.0 to 6.5.4 are vulnerable and exploitable. Versions 7.0.0 to 7.1.3 contain the vulnerability but are not exploitable due to specific environmental conditions.
• Vulnerability Type: Session Fixation (CWE-384) leading to Remote Code Execution.
• Attack Vector: Requires an attacker to fix a session ID and then trick a legitimate user into authenticating with that ID. The RCE component would likely involve further interaction with the application’s functionality after session hijacking.
• Chaining: The vulnerability can be chained with CVE-2026-102490, suggesting a multi-step attack path for full compromise.

Detection

Detection efforts should focus on identifying unusual session activity and, more critically, post-exploitation behaviors indicative of remote code execution from the Zammad application process.

• Web Server Logs: Monitor web server access logs (e.g., Apache, Nginx) for unusual session ID patterns, repeated use of the same session ID from different source IPs, or suspicious requests immediately following a user’s login.
• Application Logs: Zammad’s internal logs may show anomalies related to session management or unexpected actions performed by a user account.
• Process Monitoring: Look for the zammad application process or its child processes (e.g., Ruby on Rails application server) spawning unexpected child processes, particularly shell interpreters (sh, bash, cmd.exe, powershell.exe) or other command-line utilities.
• File System Monitoring: Monitor for suspicious file writes or modifications in the Zammad application directory or web root, which could indicate webshell deployment or other persistence mechanisms.

Sigma Detection Rules

Zammad Application Spawning Shell Process (Linux)

title: Zammad Application Spawning Shell Process (Linux)
id: 52f1e6b3-c1d0-48e0-a7d0-a0a1b2c3d4e5
status: experimental
description: Detects suspicious shell process execution originating from the Zammad application process, indicative of remote code execution (RCE).
logsource:
  product: linux
  service: auditd
detection:
  selection:
    type: 'EXECVE'
    pcomm|contains: # Adjust based on actual Zammad parent process name (e.g., 'zammad', 'puma', 'rails')
      - 'zammad'
      - 'puma'
      - 'rails'
    comm|endswith:
      - 'sh'
      - 'bash'
      - 'dash'
      - 'zsh'
      - 'python'
      - 'perl'
      - 'php'
      - 'ruby'
  condition: selection
level: high

Zammad Application Spawning Command Interpreter (Windows)

title: Zammad Application Spawning Command Interpreter (Windows)
id: 6a7b8c9d-e0f1-4234-5678-90a1b2c3d4e6
status: experimental
description: Detects suspicious command interpreter execution originating from the Zammad application process, indicative of remote code execution (RCE) on Windows environments.
logsource:
  product: windows
  service: sysmon
detection:
  selection:
    EventID: 1
    ParentImage|contains: # Adjust based on actual Zammad parent process name (e.g., 'zammad.exe', 'ruby.exe')
      - 'zammad.exe'
      - 'ruby.exe'
    Image|endswith:
      - '\cmd.exe'
      - '\powershell.exe'
      - '\pwsh.exe'
  condition: selection
level: high

Mitigations

Prioritize patching and implement robust security practices to defend against this vulnerability.

1. Patch Zammad: Upgrade Zammad to a patched version immediately. While specific patch versions are not detailed in the provided source, monitor Zammad’s official channels for security releases addressing CVE-2026-102489.
2. Implement Session Management Best Practices: Ensure Zammad’s session management is configured to generate new session IDs upon successful authentication and invalidate old ones. If Zammad’s configuration allows, enforce secure session cookie attributes (e.g., HttpOnly, Secure, SameSite).
3. Network Segmentation: Isolate the Zammad application server on a dedicated network segment with strict ingress/egress filtering to limit potential lateral movement post-exploitation.
4. Least Privilege: Ensure the zammad user and associated processes run with the absolute minimum necessary privileges to perform their functions.
5. Web Application Firewall (WAF): Deploy a WAF in front of Zammad to help detect and block known attack patterns, although it may not prevent sophisticated session fixation or RCE attempts without specific rules.

References

• https://nvd.nist.gov/vuln/detail/CVE-2026-102489
• https://csirt.divd.nl/CVE-2026-102489
• https://csirt.divd.nl/DIVD-2026-00015

Indicators of Compromise

No public IOCs available at time of writing.

MITRE ATT&CK

• T1190 — Exploit Public-Facing Application
• T1059 — Command and Scripting Interpreter