Description
An issue was discovered in Squid 3.x and 4.x through 4.8. It allows attackers to smuggle HTTP requests through frontend software to a Squid instance that splits the HTTP Request pipeline differently. The resulting Response messages corrupt caches (between a client and Squid) with attacker-controlled content at arbitrary URLs. Effects are isolated to software between the attacker client and Squid. There are no effects on Squid itself, nor on any upstream servers. The issue is related to a request header containing whitespace between a header name and a colon.
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 | 4.9-1 | — |
| Debian 13 | squid | 4.9-1 | — |
| Debian 12 | squid | 4.9-1 | — |
| Debian 10 | squid | 4.6-1+deb10u2 | DSA-4682-1 |
| Debian 9 | squid3 | 3.5.23-5+deb9u2 | DLA-2278-1 |
Show 1 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 8 | squid3 | 3.4.8-6+deb8u9 | DLA-2028-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | squid | 4.9-2ubuntu1 | — |
| Ubuntu 18.04 LTS | squid3 | 3.5.27-1ubuntu1.4 | USN-4213-1 |
| Ubuntu 16.04 LTS | squid3 | 3.5.12-1ubuntu7.9 | USN-4213-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 8 | libecap +1 | 1.0.1-2.module+el8.1.0+4044+36416a77 | RHSA-2020:4743 |
| RHEL 8 | squid | 7:4.11-3.module+el8.3.0+7851+7808b5f9 | RHSA-2020:4743 |
AlmaLinux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux 8 | libecap +1 | 1.0.1-2.module_el8.6.0+2741+01592ae8 | ALSA-2020:4743 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 8 | libecap | 1.0.1-2.module+el8.4.0+404+316a0dc5 | RLSA-2020:4743 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP1 | squid | 4.9-5.11.1 | SUSE-SU-2019:2975-1 |
| SLES 15 | squid | 4.9-5.11.1 | SUSE-SU-2019:2975-1 |
| SLES 12 SP5 | squid | 4.9-4.3.2 | SUSE-SU-2019:3067-1 |
| SLES 12 SP4 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
| SLES 12 SP3 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
Show 12 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 12 SP2 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
| SLES 11 SP4 | squid3 | 3.1.23-8.16.37.12.1 | SUSE-SU-2020:14460-1 |
| SLES for SAP 12 SP5 | squid | 4.9-4.3.2 | SUSE-SU-2019:3067-1 |
| SLES for SAP 12 SP4 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
| SLES for SAP 12 SP3 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
| SLES for SAP 12 SP2 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
| SUSE OpenStack Cloud Crowbar 8 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
| SUSE OpenStack Cloud 8 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
| SUSE OpenStack Cloud 7 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
| SUSE Linux Enterprise Point of Sale 11 SP3 | squid3 | 3.1.23-8.16.37.12.1 | SUSE-SU-2020:14460-1 |
| SUSE HPE Helion OpenStack 8 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
| SUSE Enterprise Storage 5 | squid | 3.5.21-26.20.1 | SUSE-SU-2020:0661-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | squid | 4.16-1.5 | openSUSE-SU-2024:11403-1 |
| openSUSE Leap 15.1 | squid | 4.9-lp151.2.7.1 | openSUSE-SU-2019:2541-1 |
| openSUSE Leap 15.0 | squid | 4.9-lp150.13.1 | openSUSE-SU-2019:2540-1 |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2 | squid +2 | 7:3.5.20-17.amzn2.7.10 | ALAS2-2023-2318 |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 8 | libecap +1 | 1.0.1-2.module+el8.3.0+7819+eb7d4ef6 | ELSA-2020-4743 |
| Oracle Linux 8 | squid | 7:4.11-3.module+el8.3.0+7819+eb7d4ef6 | ELSA-2020-4743 |
Advisories 17
- ALSA-2020:4743 Moderate: squid:4 security, bug fix, and enhancement update AlmaLinux Security Advisories · Oct 29, 2026
- RHSA-2020:4743 Red Hat Security Advisory: squid:4 security, bug fix, and enhancement update Red Hat Security Advisories (RHSA) · Jul 4, 2026
- DSA-4682-1 squid - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-2278-1 squid3 - security update Debian Security (DSA / DLA) · Mar 9, 2026
- DLA-2028-1 squid3 - security update Debian Security (DSA / DLA) · Mar 9, 2026
- USN-4213-1 squid, squid3 vulnerabilities Ubuntu Security Notices (USN) · Feb 10, 2026
- RLSA-2020:4743 Moderate: squid:4 security, bug fix, and enhancement update Rocky Linux Security Advisories · Feb 4, 2026
- openSUSE-SU-2024:11403-1 squid-4.16-1.5 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2020:0661-1 Security update for squid SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2019:2541-1 Security update for squid SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2019:3067-1 Security update for squid SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2019:2975-1 Security update for squid SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2019:2540-1 Security update for squid SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2020:14460-1 Security update for squid3 SUSE / openSUSE Security Updates · May 2, 2025
- ALAS2-2023-2318 Critical: squid security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Nov 6, 2023
- WID-SEC-2023-1391 Squid: Mehrere Schwachstellen BSI CERT-Bund (WID) · Oct 26, 2023
- ELSA-2020-4743 Moderate: squid:4 security, bug fix, and enhancement update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Nov 10, 2020
References
- https://github.com/squid-cache/squid/pull/445
- https://bugzilla.suse.com/show_bug.cgi?id=1156323
- http://www.squid-cache.org/Versions/v4/changesets/squid-4-671ba97abe929156dc4c717ee52ad22fba0f7443.patch
- http://www.squid-cache.org/Advisories/SQUID-2019_10.txt
- USN-4213-1 vendor-advisory
- FEDORA-2019-0b16cbdd0e vendor-advisory
- FEDORA-2019-9538783033 vendor-advisory
- [debian-lts-announce] 20191210 [SECURITY] [DLA 2028-1] squid3 security update mailing-list
- GLSA-202003-34 vendor-advisory
- DSA-4682 vendor-advisory
- [debian-lts-announce] 20200710 [SECURITY] [DLA 2278-1] squid3 security update mailing-list