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Fencer Vulns
high 8.6

CVE-2023-49288 json

Denial of Service in HTTP Collapsed Forwarding in Squid

published 2023-12-04 2 y ago modified 2026-06-17 4 mo ago also EUVD-2023-53281

cvss
8.6
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
4.8%
EPSS 4.8% chance of exploitation in 30 days, percentile 91%
public exploits
0
none known

Summary

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.

Patch / fix

  • squid Debian 14, Debian 13 6.1-1

debian advisories DEBIAN-CVE-2023-49288

  • squid Ubuntu 20.04 LTS 4.10-1ubuntu1.12
  • squid Ubuntu 22.04 LTS 5.7-0ubuntu0.22.04.4

ubuntu advisories UBUNTU-CVE-2023-49288

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • squid RHEL 8 7:4.15-7.module+el8.9.0+20806+014d88aa.3
  • libecap RHEL 8 1.0.1-2.module+el8.9.0+19703+a1da7223
  • squid RHEL 9 7:5.5-6.el9_3.2

red hat advisories RHSA-2023:7668RHSA-2023:7465

  • squid SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +5 more 5.7-150400.3.41.1

suse advisories SUSE-SU-2026:4909-1

  • squid openSUSE Tumbleweed 6.6-2.1

opensuse advisories openSUSE-SU-2024:13631-1

  • squid AlmaLinux 8 7:4.15-7.module_el8.9.0+3696+b881db49.3
  • libecap AlmaLinux 8 1.0.1-2.module_el8.6.0+2741+01592ae8
  • libecap AlmaLinux 8 1.0.1-2.module_el8.6.0+3048+383bc947

almalinux advisories ALSA-2023:7668

  • squid Alpine 3.24, Alpine 3.23, Alpine 3.22 +3 more 6.1-r0

alpine advisories ALPINE-CVE-2023-49288

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2023-49288 updated cvss 7.5

squid: Use-After-Free in the HTTP Collapsed Forwarding Feature

  • Red Hat Enterprise Linux 6 squid, squid34 Red Hat Enterprise Linux 7 squid, squid-sysvinit, squid-migration-script
    affected: workaround, no fix planned “To mitigate this issue, lines for the 'collapsed_forwarding' feature have to be removed from your squid.conf.”
  • Red Hat Enterprise Linux AppStream (v. 8) squid 4.15-7.module+el8.9.0+20806+014d88aa.3, libecap 1.0.1-2.module+el8.9.0+19703+a1da7223
    fixed: vendor fix “To mitigate this issue, lines for the 'collapsed_forwarding' feature have to be removed from your squid.conf.” RHSA-2023:7668
  • Red Hat Enterprise Linux AppStream (v. 9) squid 5.5-6.el9_3.2
    fixed: vendor fix “To mitigate this issue, lines for the 'collapsed_forwarding' feature have to be removed from your squid.conf.” RHSA-2023:7465

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
2 y ago

Exploit prediction

4.78% chance of exploitation in the next 30 days, higher than 91% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • squid-cache squid

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.