CVE-2019-12521

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.

• CWE-193
• CWE-787

• 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

Published

Apr 15, 2020

Last Modified

Jun 17, 2026

Status

Modified

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
• Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
• PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
• AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.

• CVE-2019-12516The slickquiz plugin through 1.3.7.1 for WordPress allows SQ…8.8
• CVE-2019-12517An XSS issue was discovered in the slickquiz plugin through …6.1
• CVE-2019-12518Anviz CrossChex access control management software 4.3.8.0 a…9.8
• CVE-2019-12519An issue was discovered in Squid through 4.7. When handling …9.8
• CVE-2019-1252An information disclosure vulnerability exists when the Wind…6.5
• CVE-2019-12520An issue was discovered in Squid through 4.7 and 5. When rec…7.5
• CVE-2019-12522An issue was discovered in Squid through 4.7. When Squid is …4.5
• CVE-2019-12523An issue was discovered in Squid before 4.9. When handling a…9.1
• CVE-2019-12524An issue was discovered in Squid through 4.7. When handling …9.8
• CVE-2019-12525An issue was discovered in Squid 3.3.9 through 3.5.28 and 4.…9.8
• CVE-2019-12526An issue was discovered in Squid before 4.9. URN response ha…9.8
• CVE-2019-12527An issue was discovered in Squid 4.0.23 through 4.7. When ch…8.8