CVE-2023-49288: Squid is a caching proxy for the Web supporting HTTP, HTTPS, FTP, and more. Affected versions of squid are subject to a a Use-After-Free bug which can...

Description

Squid is a caching proxy for the Web supporting HTTP, HTTPS, FTP, and more. Affected versions of squid are subject to a a Use-After-Free bug which can lead to a Denial of Service attack via collapsed forwarding. All versions of Squid from 3.5 up to and including 5.9 configured with "collapsed_forwarding on" are vulnerable. Configurations with "collapsed_forwarding off" or without a "collapsed_forwarding" directive are not vulnerable. This bug is fixed by Squid version 6.0.1. Users are advised to upgrade. Users unable to upgrade should remove all collapsed_forwarding lines from their squid.conf.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

4.78%

90.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-416

Affected Software

Vendor	Product	Versions
Squid-Cache	Squid	>= 3.5, <= 5.9

References

Timeline

Published: Dec 4, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-49288?

Squid is a caching proxy for the Web supporting HTTP, HTTPS, FTP, and more. Affected versions of squid are subject to a a Use-After-Free bug which can lead to a Denial of Service attack via collapsed forwarding. All versions of Squid from 3.5 up to and including 5.9 configured with "collapsed_forwarding on" are vulnerable. Configurations with "collapsed_forwarding off" or without a "collapsed_forwarding" directive are not vulnerable. This bug is fixed by Squid version 6.0.1. Users are advised to upgrade. Users unable to upgrade should remove all collapsed_forwarding lines from their squid.conf.

How severe is CVE-2023-49288?

CVE-2023-49288 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 4.78% probability of exploitation in the next 30 days.

How do I fix CVE-2023-49288?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.