CVE-2019-12521

Name: CVE-2019-12521
Creator: NVD / NIST
Published: 2020-04-15T19:15:12.393+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.9/10EPSS 5.76%

Last modified Jun 17, 2026

CVE-2019-12521 is a medium-severity vulnerability rated 5.9/10 on the CVSS scale. An issue was discovered in Squid through 4.7. When Squid is parsing ESI, it keeps the ESI elements in ESIContext. EPSS estimates a 5.76% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

5.9/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

5.76%

92.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Squid-Cache	Squid	>= 3.0, <= 3.5.28
Squid-Cache	Squid	>= 4.0, <= 4.7
Squid-Cache	Squid	>= 5.0, <= 5.0.1
Canonical	Ubuntu Linux	16.04
Canonical	Ubuntu Linux	18.04
Canonical	Ubuntu Linux	19.10
Canonical	Ubuntu Linux	20.04
Debian	Debian Linux	9.0
Debian	Debian Linux	10.0
Opensuse	Leap	15.1

References

http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00018.htmlMailing List, Third Party Advisory
http://www.openwall.com/lists/oss-security/2020/04/23/1Mailing List, Patch, Third Party Advisory
https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12521.txtThird Party Advisory
https://lists.debian.org/debian-lts-announce/2020/07/msg00009.htmlMailing List, Third Party Advisory
https://security.gentoo.org/glsa/202005-05Third Party Advisory
https://security.netapp.com/advisory/ntap-20210205-0006/Third Party Advisory
https://usn.ubuntu.com/4356-1/Third Party Advisory
https://www.debian.org/security/2020/dsa-4682Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00018.htmlMailing List, Third Party Advisory
http://www.openwall.com/lists/oss-security/2020/04/23/1Mailing List, Patch, Third Party Advisory
https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12521.txtThird Party Advisory
https://lists.debian.org/debian-lts-announce/2020/07/msg00009.htmlMailing List, Third Party Advisory
https://security.gentoo.org/glsa/202005-05Third Party Advisory
https://security.netapp.com/advisory/ntap-20210205-0006/Third Party Advisory
https://usn.ubuntu.com/4356-1/Third Party Advisory
https://www.debian.org/security/2020/dsa-4682Third Party Advisory

Timeline

Published: Apr 15, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2019-12521?

How severe is CVE-2019-12521?

CVE-2019-12521 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 5.76% probability of exploitation in the next 30 days.

How do I fix CVE-2019-12521?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2019-12521?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST