A new vulnerability has been identified and is abbreviated, CVE-2021-46312, which involves an issue discovered in DjvuLibre version 3.5.28. DjvuLibre is an open-source software suite that deals primarily with the DjVu image file format. This format offers several advantages, like allowing for high-quality images at smaller file sizes and enabling the storage of multiple images in a single file. Unfortunately, the vulnerability allows attackers to cause a denial of service (DoS) through a divide-by-zero situation in the IW44EncodeCodec.cpp file.

In this detailed post, we will take a closer look at how CVE-2021-46312 vulnerability can be exploited, providing code snippets, links to original references, and detailed information about the exploit.

Exploit Details

The divide-by-zero vulnerability in the IW44EncodeCodec.cpp file can be triggered if an attacker crafts a malicious DjVu file, specifically constructed to exploit the issue. When the victim opens this crafted file using DjvuLibre, the application crashes due to the divide-by-zero error.

The vulnerability can be found in the following code snippet

int IW44EncodeCodec::Impl::encode_chunk(int w, int h, int ref)
   int band = log2((w + 7) / 8);

The issue lies in the calculation of the "band" variable. If the user supplies a value of 1 for the "w" parameter, then the expression computes as:

band = log2((1 + 7) / 8);

Which simplifies to

band = log2(1);

And finally results in the following

band = ;

This zero value for "band" propagates through the rest of the function and eventually causes a divide-by-zero error.

Here are the original references that discuss the CVE-2021-46312 vulnerability

1. NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2021-46312
2. CVE Details: https://www.cvedetails.com/cve/CVE-2021-46312/
3. Mitre CVE entry: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-46312

Mitigation Techniques

The best solution for the CVE-2021-46312 vulnerability is to update DjvuLibre to the latest version available or apply a patch provided by the software maintainers. The software developers are already aware of the issue and are actively working towards resolving it in future DjvuLibre releases.

For now, users can follow these procedural steps to minimize the risk

1. Do not open DjVu files from untrusted sources to reduce the likelihood of encountering a malicious file.


The CVE-2021-46312 vulnerability demonstrates the importance of continuous software scrutiny and the need for developers and users alike to stay informed about potential security issues. By understanding how this vulnerability can be exploited, we can better protect ourselves and the systems we rely on. Keeping your software up to date and being cautious about the files you open can go a long way in securing your digital environment.


Published on: 08/22/2023 19:16:00 UTC
Last modified on: 08/28/2023 17:40:00 UTC