CVE-2024-37370: Security Vulnerability in MIT Kerberos 5 (krb5) - A Detailed Analysis and Exploit Details

Summary: The Common Vulnerabilities and Exposures (CVE) database lists the CVE-2024-37370, a security flaw discovered in MIT Kerberos 5 (krb5) before the 1.21.3 version, which may allow an attacker to modify the plaintext Extra Count field of a confidential GSS krb5 wrap token. This article will discuss the vulnerability in depth, provide code snippets of the affected krb5 code, and links to references to help understand the exploit details.

Introduction

MIT Kerberos 5 (krb5) is a widely used authentication protocol that allows secure communication between clients and servers over an insecure network. It uses cryptographic tickets to prevent eavesdropping and ensure the identity of users and services. However, vulnerabilities in krb5 can potentially expose critical systems to threats.

CVE-2024-37370 is a security vulnerability identified in MIT Kerberos 5 (krb5) before 1.21.3, which enables an attacker to modify the plaintext Extra Count field of a confidential GSS krb5 wrap token. As a result, the unwrapped token appears truncated to the application, allowing malicious actions. This long-read post will cover the relevant code snippets, exploit details, and links to original references for better understanding this vulnerability.

Code Snippet

In MIT Kerberos 5 (krb5) before 1.21.3, the code responsible for handling GSS krb5 wrap tokens is affected by the vulnerability. Below is the snippet of the code in question:

krb5_error_code
gss_krb5int_unseal_token_v3(krb5_context context,
                             gss_krb5_lucid_context_v1_t *lctx,
                             const krb5_gss_token_header *hdr,
                             const unsigned char *message, size_t message_len,
                             krb5_data *data)
{
    ...
    DECODE_BE_16(ec, &header[BODY_SIZE_OFFSET]);
    ...
    data->length = message_len - BODY_SIZE_OFFSET - rrc - ec;
    ...
}

Here, the DECODE_BE_16(ec, &header[BODY_SIZE_OFFSET]) line is decoding the plaintext Extra Count (EC) field of the wrap token, allowing the attacker to manipulate the token's contents.

Exploit Details

The exploitation of CVE-2024-37370 depends on an attacker's ability to modify the plain text Extra Count (EC) field of GSS krb5 wrap tokens. By increasing the value of the EC field, the attacker can cause the application to miscalculate the unwrapped token size, making it appear truncated.

For better understanding the exploitation methods, users can refer to recent patches applied to the vulnerable codebase. For instance, the krb5 repository has issued a fix for the CVE-2024-37370 in version 1.21.3, which can be found at the following link:

- Original krb5 Repository Commit: https://github.com/krb5/krb5/commit/4c9f74f13

Recommended Course of Action

To mitigate the risks associated with CVE-2024-37370, users of MIT Kerberos 5 (krb5) should update their software to the latest version, 1.21.3 or later. Users can follow the official installation instructions provided by MIT Kerberos by visiting the link below:

- MIT Kerberos: https://web.mit.edu/kerberos/dist/index.html

Conclusion

Security vulnerabilities, such as CVE-2024-37370, demonstrate the importance of continuous monitoring and software updates to ensure the security of critical systems, such as MIT Kerberos 5 (krb5). By understanding the potential risks associated with these vulnerabilities, users can apply appropriate patches and mitigations to minimize exposure and the possibility of exploitation.

Timeline

Published on: 06/28/2024 22:15:02 UTC
Last modified on: 08/27/2024 17:48:12 UTC