A critical vulnerability has recently been discovered in the MongoDB C driver library, which could potentially open the door to harmful cyber attacks. The vulnerability, identified as CVE-2025-0755, affects various bson_append functions in the library and could possibly result in a buffer overflow, leading to a segmentation fault and ultimately an application crash.

This vulnerability presents a serious risk to the security and stability of any applications that rely on the affected versions of the MongoDB C driver library. Specifically, this issue impacts libbson versions prior to 1.27.5, MongoDB Server v8. versions prior to 8..1, and MongoDB Server v7. versions prior to 7..16.

In this post, we will provide context about the MongoDB C driver library, explain the technical details of the vulnerability, and offer guidance on how to mitigate it.

Background

MongoDB is a popular NoSQL database management system that is widely used for handling Big Data and high-traffic applications, thanks to its flexible schema design and horizontal scaling capabilities. The MongoDB C driver library is a C library that provides client-side functionality for interacting with MongoDB databases.

The bson_append functions in the library are used for building BSON documents, which is the native format in which MongoDB stores and transfers data. These functions are crucial for constructing queries, inserting and updating documents, and performing other operations involving BSON documents.

Technical Details

The CVE-2025-0755 vulnerability is related to the failure of certain bson_append functions to properly enforce the maximum allowable BSON document size (INT32_MAX) when performing operations that could result in an oversized BSON document. This oversight can trigger a buffer overflow, causing a segmentation fault and possibly crashing the application.

Here's an example of a code snippet showcasing one of the affected functions, bson_append_utf8()

bool bson_append_utf8 (bson_t *bson, const char *key, int32_t key_length, const char *value, int32_t length) {
  bson_iter_t iter;
  bson_validate_flags_t flags = BSON_VALIDATE_UTF8_ALLOW_NULL_BYTES;
  if (!bson_iter_init (&iter, bson) ||
      !bson_iter_append_new_utf8_key (&iter, key, key_length, value, length, flags)) {
    return false;
  }
  return true;
}

When the bson_append_utf8 function is called with a large value that could potentially cause the BSON document to exceed the maximum allowed size, the function does not validate the final size properly. This can result in a buffer overflow and ultimately a segmentation fault or application crash.

Exploit Details

An attacker who has control over the content being appended to a BSON document could exploit this vulnerability by crafting a malicious BSON document that exceeds the maximum allowed size (INT32_MAX). When the vulnerable library attempts to process the malicious document, it would trigger a buffer overflow, leading to a segmentation fault and the subsequent application crash.

This vulnerability poses a risk to applications interacting with user-generated BSON content, as an attacker could potentially use it to cause a denial of service or potentially exploit the buffer overflow for code execution. As such, it is crucial to address this issue as soon as possible.

Mitigation

The vulnerability has been fixed in libbson v1.27.5, MongoDB Server v8..1, and MongoDB Server v7..16. Users of the affected versions should update their MongoDB C driver library immediately to the latest available version. To update, follow the installation instructions provided in the official MongoDB C driver documentation.

In addition to updating the library, developers should exercise caution when handling user-generated content in their applications. Ensure that proper input validation and sanitation measures are in place to handle any potential malicious input.

Conclusion

CVE-2025-0755 represents a serious vulnerability in the MongoDB C driver library that can result in buffer overflows and application crashes. Addressing this vulnerability is vital for maintaining the security and stability of applications utilizing the affected library. By updating to the latest version and implementing robust input validation measures, developers can help protect their applications from potential harm.

Timeline

Published on: 03/18/2025 09:15:11 UTC