{"id":"CVE-2019-12521","url":"https://www.cyber-defence.io/tools/cve/CVE-2019-12521","generatedAt":"2026-10-29T00:57:35.657Z","title":"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.","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.","published":"2020-04-15T19:15:12.000Z","lastModified":"2026-06-17T02:14:49.000Z","status":"Modified","sourceIdentifier":"cve@mitre.org","cvss":{"version":"3.1","score":5.9,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H"},"cwe":["CWE-193","CWE-787"],"affected":["squid-cache/squid","canonical/ubuntu linux","debian/debian linux","opensuse/leap"],"epss":{"score":0.05909,"percentile":0.93193,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (5.91%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00018.html","tags":["Mailing List","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"http://www.openwall.com/lists/oss-security/2020/04/23/1","tags":["Mailing List","Patch","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12521.txt","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://lists.debian.org/debian-lts-announce/2020/07/msg00009.html","tags":["Mailing List","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://security.gentoo.org/glsa/202005-05","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://security.netapp.com/advisory/ntap-20210205-0006/","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://usn.ubuntu.com/4356-1/","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://www.debian.org/security/2020/dsa-4682","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00018.html","tags":["Mailing List","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"http://www.openwall.com/lists/oss-security/2020/04/23/1","tags":["Mailing List","Patch","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://gitlab.com/jeriko.one/security/-/blob/master/squid/CVEs/CVE-2019-12521.txt","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.debian.org/debian-lts-announce/2020/07/msg00009.html","tags":["Mailing List","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://security.gentoo.org/glsa/202005-05","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://security.netapp.com/advisory/ntap-20210205-0006/","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://usn.ubuntu.com/4356-1/","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://www.debian.org/security/2020/dsa-4682","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2019-12521","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}