A newly discovered vulnerability, identified as CVE-2024-21502, affects the fastecdsa package, specifically in versions before 2.3.2. This vulnerability creates a potential security risk due to the use of an uninitialized variable on the stack. This blog post elaborates on the context of the issue, provides code examples to demonstrate the problem, and includes links to the original references. We will also discuss potential exploit scenarios, such as heap exploitation, denial of service, and arbitrary free or realloc operations.

Background

Fastecdsa is a popular package for working with Elliptic Curve Cryptography (ECC) in Python applications. Unfortunately, certain versions of the fastecdsa package could be vulnerable to an uninitialized variable's use in the curvemath_mul function.

Curvemath_mul Function Vulnerability

The vulnerability occurs in the curvemath_mul function, located in the src/curveMath.c file. The following code snippet has been simplified to highlight the problem:

int curvemath_mul(int a, int b, int *prod) {
  int result;
  ... // some code that sets the value of result
  *prod = result;
  return ;
}

The curvemath_mul function takes two integers as input and returns a pointer to the product after multiplying them. In this code snippet, the result variable is used without being properly initialized, leading to undefined behavior.

An attacker who has control over the stack can exploit this vulnerability in various ways, such as

1. Arbitrary free(): Depending on the uninitialized variable's actual value, an attacker may affect an arbitrary free() operation on the program's memory.
2. Arbitrary realloc(): Similar to an arbitrary free(), an attacker could potentially realloc() memory with a chosen size and location.
3. Null pointer dereference: If the uninitialized variable's value corresponds to a null pointer, it can be used to crash the program.
4. Heap exploitation: By corrupting allocator structures, the attacker could manipulate the control flow of the program, possibly leading to arbitrary code execution.

Mitigation and Recommendations

The vulnerability has been fixed in fastecdsa version 2.3.2. Users are strongly encouraged to upgrade their fastecdsa package to the latest version. If updating is not possible, consider implementing a workaround to sanitize and validate input to the curvemath_mul function.

Original References

1. Fastecdsa GitHub Repository: https://github.com/AntonKueltz/fastecdsa
2. Fixed Version: https://github.com/AntonKueltz/fastecdsa/releases/tag/2.3.2
3. NVD - National Vulnerability Database: Browsable CVE archive: https://nvd.nist.gov/vuln/detail/CVE-2024-21502

Conclusion

CVE-2024-21502 highlights the importance of proper coding practices and the consequences of using uninitialized variables in applications such as fastecdsa. To minimize the risk of exploitation, update to fastecdsa version 2.3.2 or implement an appropriate workaround. Stay vigilant and periodically check for updates to ensure your systems remain protected against emerging threats.

Timeline

Published on: 02/24/2024 05:15:44 UTC
Last modified on: 02/26/2024 13:42:22 UTC