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Vulnerability record · CVE-2019-12521 · published 15 April 2020

CVE-2019-12521: Squid-cache squid out-of-bounds write vulnerability

Squid Cache · Squid

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.

5.9 CVSS 3.1 Medium EPSS 5.9% · top 7.0% CWE-193 · CWE-193CWE-787 · Out-of-bounds write
5.9CVSS 3.1 base score, v2 4.3
5.9%EPSS exploitation probability, 30 days
NoNot in CISA KEV
4Affected product versions listed by NVD
16References
17 Jun 2026Last modified by NVD

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.

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

Affected products

4 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00018.html Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2020/04/23/1 Mailing ListPatchThird Party Advisory
https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12521.txt Third Party Advisory
https://lists.debian.org/debian-lts-announce/2020/07/msg00009.html Mailing ListThird Party Advisory
https://security.gentoo.org/glsa/202005-05 Third 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-4682 Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00018.html Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2020/04/23/1 Mailing ListPatchThird Party Advisory
https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12521.txt Third Party Advisory
https://lists.debian.org/debian-lts-announce/2020/07/msg00009.html Mailing ListThird Party Advisory
https://security.gentoo.org/glsa/202005-05 Third 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-4682 Third Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2019-12521), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.