Latest Squid caching proxy vulnerabilities #

Squid has disclosed a heap-based buffer overflow vulnerability in certain versions of the Squid caching proxy due to incorrect buffer management when processing a Uniform Resource Name (URN). This vulnerability allows a remote server to perform a buffer overflow attack by delivering specially crafted URN Trivial-HTTP responses. Successful exploitation may lead to remote code execution (RCE) or the disclosure of up to 4KB of data from Squid's allocated heap memory. This leaked memory may contain security credentials or other confidential data. This vulnerability has been designated CVE-2025-54574 and has been rated critical with a CVSS score of 9.3.

The following versions are affected

  • Squid 2.x versions up to and including 2.7.STABLE9
  • Squid 3.x versions up to and including 3.5.28
  • Squid 4.x versions up to and including 4.17
  • Squid 5.x versions up to and including 5.9
  • Squid 6.x versions up to and including 6.3

What is the impact? #

Successful exploitation of the vulnerability would allow an adversary to execute arbitrary code on the vulnerable host, potentially leading to complete system compromise.

Are updates or workarounds available? #

Users are encouraged to update to the latest version as quickly as possible:

  • Squid 6.x upgrade to version 6.4 or later
  • For all other stable releases upgrade to the latest patch version available in the patch archives

If you are using a prepackaged version of Squid, refer to your package vendor for information on the availability of updated packages.

Workaround: Mitigate the vulnerability by disabling URN access permissions through adding the following configuration changes:

acl URN proto URN
http_access deny URN

How to find potentially vulnerable systems with runZero #

From the Software Inventory, use the following query to locate potentially impacted assets:

vendor:"Squid Cache" and product:"Squid" and version:<6.4

Written by Matthew Kienow

Matthew Kienow is a software engineer and security researcher. Matthew previously worked on the Recog recognition framework, AttackerKB as well as Metasploit's MSF 5 APIs. He has also designed, built, and successfully deployed many secure software solutions; however, often he enjoys breaking them instead. He has presented his research at various security conferences including DerbyCon, Hack In Paris, and CarolinaCon. His research has been cited by CSO, Threatpost and SC Magazine.

More about Matthew Kienow
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