A significant security flaw has been identified in HashiCorp Vault, a widely utilized tool for secrets management. This vulnerability, cataloged as CVE-2025-6203, poses a risk of denial-of-service (DoS) attacks, potentially rendering Vault servers unresponsive. The issue affects both the Community and Enterprise editions of Vault, specifically versions from 1.15.0 up to certain patched releases. Administrators are strongly advised to upgrade to the latest versions—1.20.3 (Community and Enterprise), 1.19.9, 1.18.14, or 1.16.25—to mitigate this risk.
Understanding the Vulnerability
Vault’s audit devices are integral to its operation, logging every request interaction before processing. The identified vulnerability allows an attacker to submit a JSON payload that, while adhering to the default maximum request size of 32 MiB, is intricately structured with deeply nested elements or an excessive number of entries. This complexity forces the JSON parser into extensive recursion, leading to excessive CPU and memory consumption. Consequently, the system may experience timeouts, causing the Vault server to become unresponsive.
Technical Details
The vulnerability exploits the way Vault handles JSON parsing within its audit logging mechanism. By crafting a JSON payload that is within the size limits but contains deeply nested structures or a high number of entries, an attacker can induce significant resource consumption. This excessive use of CPU and memory resources can lead to timeouts and ultimately cause the Vault server to crash.
Mitigation Strategies
To address this vulnerability, HashiCorp has introduced new configuration options for the TCP listener, allowing administrators to set limits on JSON payload complexity. These options include:
– `max_json_depth`: Defines the maximum nesting depth for JSON objects.
– `max_json_string_value_length`: Sets the maximum length for string values.
– `max_json_object_entry_count`: Specifies the maximum number of key/value pairs in a JSON object.
– `max_json_array_element_count`: Determines the maximum number of elements in a JSON array.
By configuring these parameters, administrators can prevent the excessive recursion that leads to the DoS condition. Detailed guidance on implementing these configurations is available in HashiCorp’s API documentation and the Vault upgrade guide.
Acknowledgment and Reporting
The vulnerability was responsibly reported by Darrell Bethea, Ph.D., of Indeed. HashiCorp has acknowledged this contribution and has worked diligently to address the issue.
Risk Assessment
The vulnerability has been assigned a CVSS 3.1 score of 7.5, categorizing it as high severity. The risk factors include:
– Affected Products: Vault Community and Vault Enterprise versions 1.15.0 through 1.20.2, 1.19.8, 1.18.13, and 1.16.24.
– Impact: Denial of Service.
– Exploit Prerequisites: Network access to the Vault listener and the ability to submit HTTP API requests with crafted JSON payloads.
Recommended Actions
Administrators are urged to upgrade to the patched versions of Vault to mitigate this vulnerability. The recommended versions are:
– Vault Community Edition: 1.20.3
– Vault Enterprise Edition: 1.20.3, 1.19.9, 1.18.14, or 1.16.25
Upgrading to these versions will enable built-in limits on JSON payload complexity, preventing the excessive recursion that triggers the DoS condition. Additionally, administrators should review their `max_request_size` settings and apply listener-level constraints to JSON parsing as part of a comprehensive defense strategy.
Conclusion
The discovery of CVE-2025-6203 highlights the importance of continuous monitoring and updating of security systems. By promptly upgrading to the recommended versions and configuring the new listener options, organizations can safeguard their Vault instances against potential DoS attacks. Staying vigilant and proactive in applying security patches is crucial in maintaining the integrity and availability of critical infrastructure components.
