Introduction:

A recent vulnerability has been identified in the Raptor RDF Syntax Library with the Common Vulnerabilities and Exposure ID CVE-2024-57823. This vulnerability involves an integer underflow when normalizing a URI with the turtle parser in the raptor_uri_normalize_path() function. The internal details, possible exploit scenarios, and references related to this vulnerability are covered in this long-read post. Patches in the original library source code can mitigate this vulnerability. Users of Raptor RDF Syntax Library 2..16 and earlier should update the library to the latest version and apply the mitigation strategies discussed in this post.

Details of CVE-2024-57823 vulnerability

The Raptor RDF Syntax Library (official website) is a popular open-source C library that provides support for reading and writing various Resource Description Framework (RDF) syntaxes. Developers often use the library in applications that need to process RDF data, such as semantic web applications and data manipulation tools.

The vulnerability (CVE-2024-57823) stems from an integer underflow error while normalizing a URI with the turtle parser in the raptor_uri_normalize_path() function. An attacker can exploit this vulnerability by crafting a malicious URI that, when parsed and normalized by the library, triggers the underflow and causes unexpected behavior in the application. The consequences of exploiting this vulnerability could potentially lead to the crashing of the application, memory corruption or access, and unauthorized access to sensitive information.

Code snippet highlighting the underflow bug in raptor_uri_normalize_path()

Let's take a look at the code snippet (from the original vulnerable version) to understand the problem:

unsigned char *
raptor_uri_normalize_path(const unsigned char *path, size_t *normalized_path_len_p)
{
  ...
  
  length = strlen((const char *) path); /* Length of input path */

  /* Allocate required memory */
  new_path = (unsigned char *) raptor_malloc(sizeof(unsigned char) * (length + 1));

  ...
  
  for (i = ; i < length; ) {
    int n = ...; /* Process current character in path */
    
    if (n < ) {
        /* Key vulnerability: Integer underflow when n is large enough */
        i -= (-n); /* Index decrement that could result in underflow */
    } else {
        i++; /* Increment index */
    }
  }

  ...

  return new_path;
}

In the above code snippet, if the variable 'n' evaluates to a large enough negative value, the resulting decrement (i -= (-n)) could cause an underflow in the 'i' variable. This underflow could subsequently make the loop to run indefinitely, consume excessive memory, or lead to memory corruption.

Exploit details

Exploiting this vulnerability requires crafting a malicious URI in such a way that, when passed to the vulnerable raptor_uri_normalize_path() function, it triggers the integer underflow. A possible exploit scenario is where a malicious actor manages to supply the application with a specially crafted URI, either through user input or other data sources. Once the malformed URI is processed by the vulnerable raptor library, it could cause the application to crash, disclose sensitive information, or exhibit undefined behavior.

Mitigation and patches

The best course of action is to update the Raptor RDF Syntax Library to the latest version, which includes the necessary patches to prevent this vulnerability. Users can download the updated library from the official Raptor RDF Syntax Library downloads page.

Applying the following patch can also mitigate the vulnerability

@@ -1,6 +1,10 @@
 for (i = ; i < length; ) {
    int n = ...; /* Process current character in path */
    
-   if (n < ) {
+   /* Check if decrementing i will cause an underflow before subtracting. */
+   if (n <  && (size_t)-n <= i) {
        i -= (-n); /* Index decrement that could result in underflow */
    } else {
        i++; /* Increment index */
    }
}

This patch adds a simple check to ensure that the decrement operation will not cause an underflow in the 'i' variable, thus eliminating the vulnerability.

- Official Raptor RDF Syntax Library website
- Raptor RDF Syntax Library downloads page
- CVE-2024-57823 details in the National Vulnerability Database

Conclusion

CVE-2024-57823 is a significant vulnerability in the Raptor RDF Syntax Library through version 2..16 that involves an integer underflow during URI normalization with the turtle parser. Users of the library should update to the latest version and apply the necessary patches to prevent potential exploitation and resulting crashes, memory corruption or unauthorized access.

Timeline

Published on: 01/10/2025 13:15:10 UTC
Last modified on: 01/10/2025 14:15:29 UTC