A critical security flaw has been identified in the Insomnia API Client, a widely-used tool for API testing and development. This vulnerability, designated as CVE-2025-1087 with a CVSS score of 9.3, allows attackers to execute arbitrary code on a user’s system through malicious template injection. Despite multiple patch attempts, the issue persists in version 11.2.0 of the application.
Understanding the Vulnerability
Insomnia utilizes the Nunjucks templating engine to process environment variables and dynamic content within API requests. The vulnerability arises from insufficient input validation when handling template strings, enabling attackers to inject and execute arbitrary JavaScript code within the application’s context. This can lead to unauthorized access to sensitive data, manipulation of application functionality, and potential system compromise.
Attack Vectors
The vulnerability can be exploited through two primary methods:
1. Importing Malicious Collection Files: Attackers can craft and distribute API collection files containing malicious template expressions. When a user imports such a file into Insomnia, the embedded code executes, compromising the system.
2. Malicious HTTP Responses: An attacker-controlled server can respond to Insomnia’s HTTP requests with headers containing crafted cookies. These cookies, embedded with malicious template expressions, are stored in Insomnia’s cookie jar. Upon subsequent requests, the templating engine processes these expressions, leading to code execution.
Exploitation Mechanism
The exploitation process involves the following steps:
1. Crafting the Payload: Attackers create a template expression that, when processed, executes arbitrary JavaScript code. For example:
“`
{{range.constructor(return require(‘child_process’).execSync(‘command’))()}}
“`
This expression leverages JavaScript’s `range.constructor` method to escape the template sandbox and execute system commands.
2. Delivering the Payload: The malicious template can be delivered through:
– Collection Files: Distributing API collection files with embedded malicious templates.
– HTTP Responses: Sending HTTP responses with `Set-Cookie` headers containing the malicious template.
3. Execution: When Insomnia processes the template during subsequent operations, the embedded code executes, granting the attacker control over the system.
Discovery and Reporting
Security researchers Marcio Almeida and Justin Steven from Tantosec identified this vulnerability during routine API penetration testing. They reported that attackers could achieve remote code execution with minimal user interaction, posing significant risks to developers and security professionals who import shared API collections or interact with untrusted endpoints.
Mitigation Efforts and Challenges
Kong’s development team has made several attempts to mitigate this vulnerability:
– Blocking Specific Strings: Initial patches aimed to block the string require to prevent the use of Node.js modules. However, researchers bypassed this by using alternative methods like `joiner.constructor`.
– Web Worker Sandbox: Implementing a web worker sandbox to restrict available modules. Despite this, attackers found ways to escape the sandbox and execute arbitrary code.
These challenges highlight the inherent difficulties in securing client-side templating engines against injection attacks, especially when processing untrusted data.
Recommendations for Users
Given the persistent nature of this vulnerability, users are advised to:
1. Update Insomnia: Regularly check for and apply updates from the official Insomnia repository, as developers continue to work on addressing this issue.
2. Exercise Caution with Imports: Avoid importing API collection files from untrusted sources. Verify the integrity and origin of any files before importing them into Insomnia.
3. Monitor Network Interactions: Be cautious when sending requests to unfamiliar servers, as they may respond with malicious payloads designed to exploit this vulnerability.
4. Implement Input Validation: Where possible, implement strict input validation to prevent the processing of untrusted template expressions.
Conclusion
The discovery of CVE-2025-1087 underscores the critical importance of securing development tools against potential vulnerabilities. As Insomnia is widely used by developers and security professionals, ensuring its security is paramount. Users must remain vigilant, apply updates promptly, and exercise caution when interacting with untrusted data sources to mitigate the risks associated with this vulnerability.
