Turms AI-Serving module v0.10.0-SNAPSHOT and earlier contains an improper file type validation vulnerability in the OCR image upload functionality. The OcrController in turms-ai-serving/src/main/java/im/turms/ai/domain/ocr/controller/OcrController.java uses the @FormData(contentType = MediaTypeConst.IMAGE) annotation to restrict uploads to image files, but this constraint is not properly enforced. The system relies solely on client-provided Content-Type headers and file extensions without validating actual file content using magic bytes (file signatures). An attacker can upload arbitrary file types including executables, scripts, HTML, or web shells by setting the Content-Type header to image/* or using an image file extension. This bypass enables potential server-side code execution, stored XSS, or information disclosure depending on how uploaded files are processed and served.
Weakness
The product allows the upload or transfer of dangerous file types that are automatically processed within its environment.
Potential Mitigations
- Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
- When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
- Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- For example, limiting filenames to alphanumeric characters can help to restrict the introduction of unintended file extensions.
- Run the code in a “jail” or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.
- OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.
- This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.
- Be careful to avoid CWE-243 and other weaknesses related to jails.
References