CVE-2024-3651: Quadratic Complexity Vulnerability in kjd/idna Library idna.encode() Function

A newly discovered vulnerability, dubbed as CVE-2024-3651, has been found within the widely-used kjd/idna library. This package is responsible for encoding and decoding of Internationalized Domain Names (IDN) under the IDNA2008 protocol, which is implemented in various applications.

The vulnerability specifically affects the idna.encode() function handling of specially crafted input strings, leading to a quadratic complexity attack, that can result in a denial of service (DoS) condition, slowing down applications and services, and potentially causing complete unavailability.

In this article, we will explore the details of this vulnerability, analyze the problematic section within the idna.encode() function, and discuss the implications of this vulnerability on affected applications.

Vulnerability Details

Vulnerable Library: kjd/idna
Affected Function: idna.encode()
Affected Version: 3.6
Vulnerability Type: Denial of Service (DoS) due to Quadratic Complexity
CVE ID: CVE-2024-3651

The vulnerability has been found in the popular kjd/idna library that is used for encoding/decoding of Internationalized Domain Names. A crafted input string can cause the idna.encode() function to perform at a significant computational load, increasing the processing time in a quadratic manner relative to the input size, leading to a denial of service condition.

The following code snippet demonstrates the problematic section within the idna.encode() function

def encode(input: str) -> List[Text]:
    labels = _utext(input).split(".")
    result = []
    for label in labels:
        result.append("".join(ustr(lookup(x)) for x in _label_decode(label)))
    return result

More details about the vulnerability can be found in the official advisory, explaining the exploitation scenario and its impact.

Exploitation Details

An attacker can leverage this vulnerability by supplying a specially crafted input string to an application utilizing the idna.encode() function. The crafted input causes the function to process the input with considerable computational load, significantly increasing the processing time in a quadratic manner relative to the input size.

As a result, the affected application will become unresponsive or function extremely slowly, leading to a denial of service for the end-users. The vulnerability can have various impacts depending on the specific usage of the affected library in different applications.

Mitigation and Recommendations

Currently, no official patch has been released to address CVE-2024-3651. However, it is recommended to apply the following mitigation measures until a patch becomes available:

1. Limit the input size passed to the idna.encode() function, ensuring that only reasonably sized inputs are processed.
2. Utilize rate-limiting measures to reduce the attack surface, making it more challenging for attackers to bombard applications with crafted input strings.
3. Monitor and manage application logs to detect and react to any suspicious activity that could be an indication of exploitation of this vulnerability.

In conclusion, CVE-2024-3651 is a significant vulnerability within the kjd/idna library's idna.encode() function, leading to quadratic complexity and denial of service conditions. Applications using this library should apply appropriate mitigation measures and keep an eye out for an official patch to resolve the issue.

Timeline

Published on: 07/07/2024 18:15:09 UTC
Last modified on: 07/11/2024 14:58:01 UTC