A recently discovered security flaw in the popular open-source software library, libcurl, allows an attacker to insert cookies at will into a running program using a specific series of conditions. This vulnerability, known as CVE-2023-38546, could potentially be exploited to spoof authentication, session management, or even bypass various security mechanisms. In this article, we will take a closer look at the details of this flaw, its implications, and how developers can mitigate the risk.

Understanding the Flaw in Libcurl

Libcurl is widely used in many applications to handle network transfers, such as HTTP or FTP connections, among many others. When managing multiple transfers, libcurl provides "easy handles" in its API to work with individual transfers.

A crucial function in libcurl is the curl_easy_duphandle. This function essentially duplicates an easy handle and its settings, making it suitable for reuse. You can find official documentation by following this link.

The vulnerability lies in the way the curl_easy_duphandle function handles cookies. When a handle is duplicated, and the transfer has cookies enabled, the cookie-enable state is cloned, but the actual cookies are not. This results in a situation where cookies are unexpectedly loaded from a file named none, if such a file exists and is readable in the current directory of the application using libcurl.

Exploit Details

In order to exploit this vulnerability, an attacker can create a file named none with the correct cookie file format. If the attacker manages to place this file in the current directory of a vulnerable application using libcurl, they will be able to insert cookies at will.

Here's an example of how this code snippet creates a vulnerability

CURL *orig_handle = curl_easy_init();
curl_easy_setopt(orig_handle, CURLOPT_COOKIEFILE, "");
CURL *cloned_handle = curl_easy_duphandle(orig_handle);

// The cloned_handle will now look for cookies in a file named 'none'

How to Mitigate the Risk

To mitigate the risk of this vulnerability, developers should ensure that they specify the correct source for loading cookies when using the curl_easy_duphandle function. For example, you can set the CURLOPT_COOKIEFILE option to an empty string or a specific file path, which forces libcurl not to use the file named none:

CURL *orig_handle = curl_easy_init();
curl_easy_setopt(orig_handle, CURLOPT_COOKIEFILE, "");
CURL *cloned_handle = curl_easy_duphandle(orig_handle);
curl_easy_setopt(cloned_handle, CURLOPT_COOKIEFILE, ""); // Set the cookie source explicitly

// The cloned_handle will not use the 'none' file for cookies

Developers should also periodically review and update their libcurl dependencies to ensure they are not affected by new CVEs or vulnerabilities.


CVE-2023-38546 is a concerning vulnerability in libcurl that could potentially harm many applications if exploited. Understanding the details of the flaw, how it can be exploited, and how to mitigate the risk is essential to keeping your applications safe. By specifying the correct source for loading cookies and keeping your libcurl dependencies up to date, you can protect your applications from this vulnerability.


Published on: 10/18/2023 04:15:00 UTC
Last modified on: 10/28/2023 03:15:00 UTC