Description
An issue was discovered in Squid through 4.7. When Squid is parsing ESI, it keeps the ESI elements in ESIContext. ESIContext contains a buffer for holding a stack of ESIElements. When a new ESIElement is parsed, it is added via addStackElement. addStackElement has a check for the number of elements in this buffer, but it's off by 1, leading to a Heap Overflow of 1 element. The overflow is within the same structure so it can't affect adjacent memory blocks, and thus just leads to a crash while processing.
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 | 4.11-1 | — |
| Debian 13 | squid | 4.11-1 | — |
| Debian 12 | squid | 4.11-1 | — |
| 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 20.04 LTS | squid | 4.10-1ubuntu1.1 | USN-4356-1 |
| Ubuntu 18.04 LTS | squid3 | 3.5.27-1ubuntu1.6 | USN-4356-1 |
| Ubuntu 16.04 LTS | squid3 | 3.5.12-1ubuntu7.11 | USN-4356-1 |
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 | 4.11-5.17.2 | SUSE-SU-2020:1156-1 |
| SLES 15 | squid | 4.11-5.17.2 | SUSE-SU-2020:1156-1 |
| SLES 12 SP5 | squid | 4.11-4.9.1 | SUSE-SU-2020:1134-1 |
| 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 |
Show 14 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| 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 |
| SLES for SAP 15 | squid | 4.11-5.17.2 | SUSE-SU-2020:1156-1 |
| SLES for SAP 12 SP5 | squid | 4.11-4.9.1 | SUSE-SU-2020:1134-1 |
| 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 |
| SLE HPC 15 | squid | 4.11-5.17.2 | SUSE-SU-2020:1156-1 |
| 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 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Leap 15.1 | squid | 4.11-lp151.2.15.2 | openSUSE-SU-2020:0623-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.11 | squid | 4.11-r0 | — |
| Alpine v3.10 | squid | 4.11-r0 | — |
| Alpine v3.9 | squid | 4.11-r0 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2 | squid +2 | 7:3.5.20-17.amzn2.7.20 | ALAS2-2024-2509 |
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 13
- 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-4356-1 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
- SUSE-SU-2020:1227-1 Security update for squid SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2020:1134-1 Security update for squid SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2020:0623-1 Security update for squid SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2020:1156-1 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
- ALAS2-2024-2509 Important: squid security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Mar 27, 2024
- 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://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12521.txt
- [oss-security] 20200423 [ADVISORY] SQUID-2019:12 Multiple issues in ESI Response processing mailing-list
- DSA-4682 vendor-advisory
- openSUSE-SU-2020:0623 vendor-advisory
- GLSA-202005-05 vendor-advisory
- USN-4356-1 vendor-advisory
- [debian-lts-announce] 20200710 [SECURITY] [DLA 2278-1] squid3 security update mailing-list
- https://security.netapp.com/advisory/ntap-20210205-0006/