Squid, the widely-used web caching proxy server, has been found to be vulnerable to a particular Denial of Service (DoS) attack. This vulnerability, known as CVE-2023-46848, is caused by an attacker sending specially crafted FTP URLs in HTTP Request messages or constructing them from FTP Native input. In this post, we will provide detailed information about this security vulnerability, along with code snippets, links to the original references, and suggestions for mitigating the potential impact of this security issue on your Squid server.

Exploit Details

A remote attacker can exploit CVE-2023-46848 by sending HTTP requests containing malformed FTP URLs or by crafting such URLs from native FTP input. This vulnerability exists due to the improper handling of FTP URLs within the Squid proxy server. By exploiting this vulnerability, an attacker could cause the Squid server to crash, leading to a DoS condition and making the server non-functional for legitimate users.

The following code snippet is an example demonstrating how an attacker might craft an HTTP request containing a malformed FTP URL to exploit this vulnerability:

GET ftp://someserver.com/%d%aContent-Length:%200%d%a HTTP/1.1
Host: someserver.com
User-Agent: Mozilla/5. (Windows NT 10.; Win64; x64; rv:89.) Gecko/20100101 Firefox/89.
Accept: text/html,application/xhtml+xml,application/xml;q=.9,image/webp,*/*;q=.8
Accept-Language: en-US,en;q=.5
Accept-Encoding: gzip, deflate, br
Connection: close

Original References

The vulnerability, CVE-2023-46848, was first discovered and documented by [researcher's name] in a [date] security advisory. You may refer to the following links for comprehensive information about the vulnerability:


To protect your Squid server from potential attacks exploiting CVE-2023-46848, you should implement the following steps:

1. Update Squid: Ensure your Squid server is running the latest version, which includes a fix for the vulnerability. You should download and install the most recent release from the official Squid website (http://www.squid-cache.org/). Alternatively, you can use a package manager provided by your operating system to update the Squid software.

2. Firewall Rules: Configure your firewall to block traffic from suspicious IP addresses, URL patterns, or known malicious sources. Doing so can minimize the risk of an attacker reaching your Squid server to initiate an attack.

3. Intrusion Detection and Prevention (IDS/IPS) System: Employ an IDS/IPS system to detect and prevent potential attack attempts on your Squid server. A well-configured IDS/IPS solution can help identify malicious traffic and prevent these types of attacks from being successful.

4. Regular Monitoring and Log Analysis: Regularly monitor and analyze your Squid server's log files to detect any suspicious traffic patterns or unusual behavior that may indicate an attempted attack.


Security vulnerabilities like CVE-2023-46848 can pose a significant threat to your Squid server and the services it provides to end users. By staying informed about such vulnerabilities and taking the proper mitigation steps, you can minimize the risk of DoS attacks due to CVE-2023-46848 and ensure your Squid server continues to function as intended.

Keep your Squid server updated and secure, and remain vigilant against new threats and vulnerabilities!


Published on: 11/03/2023 08:15:08 UTC
Last modified on: 12/14/2023 10:15:08 UTC