Description
An issue was discovered in Squid through 4.7 and 5. When receiving a request, Squid checks its cache to see if it can serve up a response. It does this by making a MD5 hash of the absolute URL of the request. If found, it servers the request. The absolute URL can include the decoded UserInfo (username and password) for certain protocols. This decoded info is prepended to the domain. This allows an attacker to provide a username that has special characters to delimit the domain, and treat the rest of the URL as a path or query string. An attacker could first make a request to their domain using an encoded username, then when a request for the target domain comes in that decodes to the exact URL, it will serve the attacker's HTML instead of the real HTML. On Squid servers that also act as reverse proxies, this allows an attacker to gain access to features that only reverse proxies can use, such as ESI.
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 | 4.8-1 | — |
| Debian 13 | squid | 4.8-1 | — |
| Debian 12 | squid | 4.8-1 | — |
| Debian 10 | squid | 4.6-1+deb10u2 | DSA-4682-1 |
| Debian 9 | squid3 | 3.5.23-5+deb9u2 | DLA-2278-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 18.04 LTS | squid3 | 3.5.27-1ubuntu1.7 | USN-4446-1 |
| Ubuntu 16.04 LTS | squid3 | 3.5.12-1ubuntu7.12 | USN-4446-1 |
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 12 SP4 | squid | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
| SLES 12 SP3 | squid | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
| SLES 12 SP2 | squid | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
| SLES 11 SP4 | squid3 | 3.1.23-8.16.37.12.1 | SUSE-SU-2020:14460-1 |
Show 9 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 12 SP4 | squid | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
| SLES for SAP 12 SP3 | squid | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
| SLES for SAP 12 SP2 | squid | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
| SUSE OpenStack Cloud Crowbar 8 | squid | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
| SUSE OpenStack Cloud 8 | squid | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
| SUSE OpenStack Cloud 7 | squid | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
| 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 | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
| SUSE Enterprise Storage 5 | squid | 3.5.21-26.23.1 | SUSE-SU-2020:1227-1 |
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 |
| Oracle Linux 7 | squid | 7:4.11-3.0.1.el7 | ELSA-2022-22254 |
Advisories 12
- 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
- USN-4446-1 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
- SUSE-SU-2020:1227-1 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
- WID-SEC-2022-1594 Squid: Mehrere Schwachstellen BSI CERT-Bund (WID) · Oct 26, 2023
- WID-SEC-2022-1593 Squid: Mehrere Schwachstellen BSI CERT-Bund (WID) · Oct 5, 2023
- ELSA-2022-22254 Important: squid security update (Oracle Linux 7) Oracle Linux Security Advisories (ELSA) · Oct 3, 2022
- ELSA-2020-4743 Moderate: squid:4 security, bug fix, and enhancement update (Oracle Linux 8) Oracle Linux Security Advisories (ELSA) · Nov 10, 2020
References
- http://www.squid-cache.org/Versions/v4/
- http://www.squid-cache.org/Versions/v4/changesets/
- https://github.com/squid-cache/squid/commits/v4
- https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12520.txt
- DSA-4682 vendor-advisory
- [debian-lts-announce] 20200710 [SECURITY] [DLA 2278-1] squid3 security update mailing-list
- USN-4446-1 vendor-advisory
- https://security.netapp.com/advisory/ntap-20210205-0006/