A critical heap-based buffer overflow vulnerability (CVE-2022-3437) has been discovered in Samba, specifically in the GSSAPI unwrap_des() and unwrap_des3() routines of the Heimdal component. Heimdal is an alternative implementation of the GSSAPI (Generic Security Service API) used in many infrastructure systems and applications, including Samba. The vulnerability allows an attacker to send specially crafted malicious data to the application, possibly leading to a denial of service (DoS) attack.

In this post, we will dive into the details of this vulnerability, the affected code, and the potential impact on affected systems. We will also provide links to the original references and resources for further reading.

Vulnerability Details

The core issue of CVE-2022-3437 arises from the DES (Data Encryption Standard) and Triple-DES (3DES) decryption routines in the Heimdal GSSAPI library. An attacker can exploit this flaw by sending a maliciously small packet, causing a length-limited write buffer overflow on malloc() allocated memory. The primary consequences of this vulnerability are a potential denial of service (DoS) attack and possibly arbitrary code execution.

Affected Code Snippet

The buffer overflow vulnerability is rooted in the GSSAPI unwrap_des() and unwrap_des3() routines of Heimdal, which include the DES and Triple-DES decryption routines. Below is a simplified code snippet highlighting the affected section:

/* Heimdal GSSAPI library */
int
unwrap_des(mechinfo, ctx, in, out)
{
    ...allocate_memory(buffer)...
    ...check_buffer_length(buffer)...
    ...decrypt_packet(buffer, ...)... // <- Vulnerable Call
    ...process_decrypted_data(buffer)...
    free(buffer);
}

int
unwrap_des3(mechinfo, ctx, in, out)
{
    ...allocate_memory(buffer)...
    ...check_buffer_length(buffer)...
    ...decrypt_packet(buffer, ...)... // <- Vulnerable Call
    ...process_decrypted_data(buffer)...
    free(buffer);
}

References and Resources

- The Samba Project has published an advisory for CVE-2022-3437, which can be found here: Samba Security Advisory
- The official CVE database entry for this vulnerability is: CVE-2022-3437
- Heimdal's source code repository is available here: Heimdal GitHub Repository

Exploit Details

To exploit this vulnerability, an attacker must craft a malicious packet with specially designed data and send it to the targeted application, causing a write buffer overflow on malloc() allocated memory. The exploitation process might involve the following steps:

1. Analyze the target application and determine whether it uses the Heimdal GSSAPI library and is vulnerable to CVE-2022-3437 (particularly focusing on the unwrap_des() or unwrap_des3() routines).
2. Craft a malicious packet with data designed to trigger the buffer overflow vulnerability within the target application.
3. Send the malicious packet to the target application, causing a length-limited write buffer overflow on malloc() allocated memory and potentially leading to a denial of service (DoS) attack or arbitrary code execution.

Prevention and Mitigation

The best way to protect against CVE-2022-3437 is to install the latest updates and patches for the affected software. Users of affected systems and applications should download and apply the latest available updates from their respective vendors and maintain an up-to-date environment. Developers should also consider incorporating secure coding practices and implementing proper bounds checking to prevent buffer overflow vulnerabilities in future releases.

Conclusion

The heap-based buffer overflow vulnerability (CVE-2022-3437) in Samba within the GSSAPI unwrap_des() and unwrap_des3() routines of Heimdal poses a significant risk to the integrity and reliability of many systems and applications. Staying informed about the latest security updates and applying the appropriate patches in a timely manner is crucial to safeguarding your systems and applications from potential exploitation of this vulnerability.

Timeline

Published on: 01/12/2023 15:15:00 UTC
Last modified on: 02/16/2023 14:15:00 UTC