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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| squid-cache | squid | >= 3.5, < 6.0.1 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | squid | 6.1-1 | — |
| Debian 13 | squid | 6.1-1 | — |
| Debian 12 | squid | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 22.04 LTS | squid | 5.7-0ubuntu0.22.04.4 | USN-6728-1 |
| Ubuntu 20.04 LTS | squid | 4.10-1ubuntu1.12 | USN-6728-3, USN-6728-1 |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 18.04 LTS | squid3 | No fix yet | — |
| Ubuntu Pro 16.04 LTS | squid3 | No fix yet | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 9 | squid | 7:5.5-6.el9_3.2 | RHSA-2023:7465 |
| RHEL 8 | libecap +1 | 1.0.1-2.module+el8.9.0+19703+a1da7223 | RHSA-2023:7668 |
| RHEL 8 | squid | 7:4.15-7.module+el8.9.0+20806+014d88aa.3 | RHSA-2023:7668 |
AlmaLinux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux 8 | libecap +1 | 1.0.1-2.module_el8.6.0+2741+01592ae8 | ALSA-2023:7668 |
| AlmaLinux 8 | squid | 7:4.15-7.module_el8.9.0+3696+b881db49.3 | ALSA-2023:7668 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP5 | squid | 5.7-150400.3.41.1 | SUSE-SU-2026:4909-1 |
| SLES 15 SP4 | squid | 5.7-150400.3.41.1 | SUSE-SU-2026:4909-1 |
Show 4 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 15 SP5 | squid | 5.7-150400.3.41.1 | SUSE-SU-2026:4909-1 |
| SLES for SAP 15 SP4 | squid | 5.7-150400.3.41.1 | SUSE-SU-2026:4909-1 |
| SLE HPC 15 SP5 | squid | 5.7-150400.3.41.1 | SUSE-SU-2026:4909-1 |
| SLE HPC 15 SP4 | squid | 5.7-150400.3.41.1 | SUSE-SU-2026:4909-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | squid | 6.6-2.1 | openSUSE-SU-2024:13631-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | squid | 6.1-r0 | — |
| Alpine v3.23 | squid | 6.1-r0 | — |
| Alpine v3.22 | squid | 6.1-r0 | — |
| Alpine v3.21 | squid | 6.1-r0 | — |
| Alpine v3.20 | squid | 6.1-r0 | — |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.19 | squid | 6.1-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | squid | 7:6.6-1.amzn2023.0.3 | ALAS2023-2024-578 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 2 (CBL-Mariner) | squid | No fix yet | — |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 9 | squid | 7:5.5-6.el9_3.2 | ELSA-2023-7465 |
Advisories 11
- ALSA-2023:7668 Important: squid:4 security update AlmaLinux Security Advisories · Nov 6, 2026
- WID-SEC-2023-3049 Squid: Mehrere Schwachstellen ermöglichen Denial of Service BSI CERT-Bund (WID) · Oct 26, 2026
- SUSE-SU-2026:4909-1 Security update for squid SUSE / openSUSE Security Updates · Oct 26, 2026
- RHSA-2023:7668 Red Hat Security Advisory: squid:4 security update Red Hat Security Advisories (RHSA) · Jul 12, 2026
- RHSA-2023:7465 Red Hat Security Advisory: squid security update Red Hat Security Advisories (RHSA) · Jul 12, 2026
- USN-6728-1 squid vulnerabilities Ubuntu Security Notices (USN) · Apr 27, 2026
- USN-6728-3 squid vulnerability Ubuntu Security Notices (USN) · Apr 27, 2026
- openSUSE-SU-2024:13631-1 squid-6.6-2.1 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- ALAS2023-2024-578 Important: squid security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Aug 26, 2025
- WID-SEC-2024-1248 Xerox FreeFlow Print Server: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 21, 2024
- ELSA-2023-7465 Important: squid security update (Oracle Linux 9) Oracle Linux Security Advisories (ELSA) · Nov 28, 2023
References
- https://github.com/squid-cache/squid/security/advisories/GHSA-rj5h-46j6-q2g5
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/MEV66D3PAAY6K7TWDT3WZBLCPLASFJDC/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/A5QASTMCUSUEW3UOMKHZJB3FTONWSRXS/
- https://security.netapp.com/advisory/ntap-20240119-0006/