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Vulnerability record · CVE-2021-43818 · published 13 December 2021

CVE-2021-43818: Lxml injection vulnerability

LLxml · Lxml

lxml is a library for processing XML and HTML in the Python language. Prior to version 4.6.5, the HTML Cleaner in lxml.html lets certain crafted script content pass through, as well as script content in SVG files embedded using data URIs. Users that employ the HTML cleaner in a security relevant context should upgrade to lxml 4.6.5 to receive a patch. There are no known workarounds available.

7.1 CVSS 3.1 High EPSS 2.5% · top 16.1% CWE-74 · InjectionCWE-79 · Cross-site scripting
7.1CVSS 3.1 base score, v2 6.8
2.5%EPSS exploitation probability, 30 days
NoNot in CISA KEV
11Affected product versions listed by NVD
28References
17 Jun 2026Last modified by NVD

Description

lxml is a library for processing XML and HTML in the Python language. Prior to version 4.6.5, the HTML Cleaner in lxml.html lets certain crafted script content pass through, as well as script content in SVG files embedded using data URIs. Users that employ the HTML cleaner in a security relevant context should upgrade to lxml 4.6.5 to receive a patch. There are no known workarounds available.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L

Affected products

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

References

LinkTags
https://github.com/lxml/lxml/commit/12fa9669007180a7bb87d990c375cf91ca5b664a PatchThird Party Advisory
https://github.com/lxml/lxml/commit/a3eacbc0dcf1de1c822ec29fb7d090a4b1712a9c#diff-59130575b4fb2932c957db2922977d7d89afb0 PatchThird Party Advisory
https://github.com/lxml/lxml/commit/f2330237440df7e8f39c3ad1b1aa8852be3b27c0 PatchThird Party Advisory
https://github.com/lxml/lxml/security/advisories/GHSA-55x5-fj6c-h6m8 Third Party Advisory
https://lists.debian.org/debian-lts-announce/2021/12/msg00037.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TUIS2KE3HZ2AAQKXFLTJFZP
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/V2XMOM5PFT6U5AAXY6EFNT5
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WZGNET2A4WGLSUXLBFYKNC5
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZQ4SPKJX3RRJK4UWA6FXCRH
https://security.gentoo.org/glsa/202208-06 Third Party Advisory
https://security.netapp.com/advisory/ntap-20220107-0005/ Third Party Advisory
https://www.debian.org/security/2022/dsa-5043 Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpujul2022.html PatchThird Party Advisory
https://github.com/lxml/lxml/commit/12fa9669007180a7bb87d990c375cf91ca5b664a PatchThird Party Advisory
https://github.com/lxml/lxml/commit/a3eacbc0dcf1de1c822ec29fb7d090a4b1712a9c#diff-59130575b4fb2932c957db2922977d7d89afb0 PatchThird Party Advisory
https://github.com/lxml/lxml/commit/f2330237440df7e8f39c3ad1b1aa8852be3b27c0 PatchThird Party Advisory
https://github.com/lxml/lxml/security/advisories/GHSA-55x5-fj6c-h6m8 Third Party Advisory
https://lists.debian.org/debian-lts-announce/2021/12/msg00037.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TUIS2KE3HZ2AAQKXFLTJFZP
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/V2XMOM5PFT6U5AAXY6EFNT5
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WZGNET2A4WGLSUXLBFYKNC5
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZQ4SPKJX3RRJK4UWA6FXCRH
https://security.gentoo.org/glsa/202208-06 Third Party Advisory
https://security.netapp.com/advisory/ntap-20220107-0005/ Third Party Advisory
https://www.debian.org/security/2022/dsa-5043 Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpujul2022.html PatchThird Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-43818), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.