CVE-2024-47076: CUPS libcupsfilters Vulnerability – Lack of Sanitization of IPP Attributes from an IPP Server

In the world of computer systems, vulnerabilities and their corresponding exploits are not uncommon. However, it is important that these potential security weaknesses are identified, understood, and mitigated as much as possible. In this long-read post, we will discuss an identified vulnerability in the CUPS (Common Unix Printing System) and dive deep into its details, including a code snippet, explanation, original references, and exploitation possibilities. This will help provide a greater understanding of the issue and how it needs to be resolved.

Introduction to CUPS and libcupsfilters

CUPS is a standards-based, open-source printing system that is used across different platforms, providing an efficient and streamlined way for computers to communicate with printers. One core component of CUPS is the libcupsfilters library, which contains the code for numerous filters that were once a part of the cups-filters package. These filters are now available as library functions for data format conversion tasks in Printer Applications.

Link: CUPS Official Website
Link: libcupsfilters GitHub Repository

Vulnerability: CVE-2024-47076 - Lack of Sanitization of IPP Attributes from an IPP Server

The identified vulnerability, labeled as CVE-2024-47076, pertains to the cfGetPrinterAttributes5 function found in the libcupsfilters library. The issue arises due to the fact that this function does not sanitize the IPP (Internet Printing Protocol) attributes that are returned from an IPP server. As a result, when these attributes are utilized, for instance, when generating a PPD (PostScript Printer Description) file, this can lead to an attacker having the ability to supply malicious data to the rest of the CUPS system.

Link: CVE-2024-47076 - NVD

Code Snippet

Here is a simple code snippet from the libcupsfilters library, which demonstrates the lack of sanitization in the cfGetPrinterAttributes5 function:

ipp_t *                                       /* O - Attributes, NULL on error */
cfGetPrinterAttributes5(
...
)
{
...
  ippAddString(request, IPP_TAG_PRINTER, IPP_TAG_KEYWORD, "requested-attributes", NULL, CFGET_ATTRS);
...
  if ((response = cupsDoRequest(http, request, "/ipp/")))  /* Send request */
  {
...
  }
...
}

The ippAddString() function adds an IPP string attribute to the IPP request, but as you can see, the attribute values added to CFGET_ATTRS are not sanitized before being passed onto the request.

Details on Exploitation

The lack of sanitization in the libcupsfilters library provides an opportunity for an attacker to exploit the CUPS system by injecting malicious data via the unvalidated IPP attributes. This could lead to various attacks, such as:

1. Arbitrary code execution: The unsanitized data may allow executing attacker-supplied code, which could compromise the security and functionality of the entire system.
2. Data manipulation: The attacker could modify or delete the printer settings, leading to incorrect printing output or rendering the printer unusable.
3. Privilege escalation: With the ability to control data in the CUPS system, the attacker could raise their privileges on the system to gain unauthorized access to restricted resources.

Conclusion and Further Steps

The discovered vulnerability, CVE-2024-47076, in the CUPS libcupsfilters library poses a significant risk to the integrity and security of printing systems that use this library. Organizations and users relying on CUPS for their printing needs should proactively monitor for patches and updates from the maintainers that address the issue. Moreover, organizations can implement additional security measures, such as network segregation and strong authentication mechanisms, to minimize the likelihood of an attacker gaining access to the CUPS system in the first place. By taking these steps, we can ensure the security and stability of printing systems using CUPS and significantly reduce the potential impact of this vulnerability.

Timeline

Published on: 09/26/2024 22:15:04 UTC
Last modified on: 09/30/2024 12:46:20 UTC