CVE-2025-47917: Use-After-Free Vulnerability in Mbed TLS Potentially Leading to System Compromise

Overview

In this post, we delve into the details of a critical vulnerability dubbed CVE-2025-47917, which poses a significant risk to applications developed in accordance with the Mbed TLS documentation before version 3.6.4. This vulnerability possesses the capability to compromise systems and leak confidential data, making it a matter of grave concern for developers, administrators, and organizations alike.
The vulnerability is of particular concern due to its severity and the widespread usage of Mbed TLS in various applications. As businesses increasingly adopt digital solutions and cloud-based services, ensuring the security of such applications becomes paramount to prevent potential attacks and data breaches.

Vulnerability Summary

CVE ID: CVE-2025-47917
Severity: High (8.9 CVSS score)
Attack Vector: Local
Privileges Required: None
User Interaction: Required
Impact: Potential system compromise or data leakage

Affected Products

Product | Affected Versions

Mbed TLS | Before 3.6.4

How the Exploit Works

The CVE-2025-47917 vulnerability stems from a use-after-free situation in certain Mbed TLS applications developed in accordance with the documentation. The function mbedtls_x509_string_to_names() takes an argument documented as an output argument. The function, however, calls mbedtls_asn1_free_named_data_list() on that argument, which performs a deep free() operation.
This sequence of events leads to a situation where the application code, which uses this function relying on documented behavior, still holds pointers to the memory blocks that were freed. This can lead to a high risk of use-after-free or double-free situations, particularly in the two sample programs x509/cert_write and x509/cert_req. If the san string contains more than one DN, a use-after-free situation occurs.

Conceptual Example Code

Here is a conceptual example that illustrates how the vulnerability might be exploited. This is a simplified version and actual exploitation could be more complex:

#include "mbedtls/x509.h"
int main() {
mbedtls_x509_name *name;
char *san = "CN=example.com, CN=malicious.com";
// This call frees the memory pointed by 'name'
mbedtls_x509_string_to_names(&name, san);
// 'name' is now a dangling pointer
// Any access or modification to 'name' here may result in undefined behavior
// Exploits can manipulate this to take advantage or corrupt the system
return 0;
}

This code shows that the vulnerability lies in the fact that the function mbedtls_x509_string_to_names() frees the memory pointed to by ‘name’, leaving it as a dangling pointer. Any subsequent access to ‘name’ could lead to undefined behavior, which could be exploited by malicious actors.