HOMEVULNERABILITIESCVE-2021-43818
HIGH

CVE-2021-43818

CWE-74Published: December 13, 2021· Updated: Jun 17, 2026

7.1
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-43818 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

Exploitation does not require any privileges, though user interaction (Required) is needed, which slightly reduces the risk of mass automated attacks.

The vulnerability has a "Changed" scope, meaning successful exploitation can impact components beyond the vulnerable component itself — such as the host operating system or adjacent services.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionRequired
ScopeChanged
Impact
ConfidentialityLow
IntegrityLow
AvailabilityLow
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L

Affected Vendors & Products

Debian1 product(s)
debian linux
Fedora1 product(s)
fedora
lxml1 product(s)
lxml
netapp4 product(s)
solidfiresolidfire enterprise sdshci storage node firmwarehci storage node
Oracle5 product(s)
communications cloud native core binding support functioncommunications cloud native core network exposure functioncommunications cloud native core policyhttp serverzfs storage appliance kit
Source: NVD CPE · 16 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://github.com/lxml/lxml/commit/12fa9669007180a7bb87d990c375cf91ca5b664a
PATCHhttps://github.com/lxml/lxml/commit/a3eacbc0dcf1de1c822ec29fb7d090a4b1712a9c#diff-59130575b4fb2932c957db2922977d7d89afb0b2085357db1a14615a2fcad776
PATCHhttps://github.com/lxml/lxml/commit/f2330237440df7e8f39c3ad1b1aa8852be3b27c0
PATCHhttps://www.oracle.com/security-alerts/cpuapr2022.html
PATCHhttps://www.oracle.com/security-alerts/cpujul2022.html
PATCHhttps://github.com/lxml/lxml/commit/12fa9669007180a7bb87d990c375cf91ca5b664a
PATCHhttps://github.com/lxml/lxml/commit/a3eacbc0dcf1de1c822ec29fb7d090a4b1712a9c#diff-59130575b4fb2932c957db2922977d7d89afb0b2085357db1a14615a2fcad776
PATCHhttps://github.com/lxml/lxml/commit/f2330237440df7e8f39c3ad1b1aa8852be3b27c0
PATCHhttps://www.oracle.com/security-alerts/cpuapr2022.html
PATCHhttps://www.oracle.com/security-alerts/cpujul2022.html
ADVISORYhttps://github.com/lxml/lxml/security/advisories/GHSA-55x5-fj6c-h6m8
ADVISORYhttps://lists.debian.org/debian-lts-announce/2021/12/msg00037.html
ADVISORYhttps://security.gentoo.org/glsa/202208-06
ADVISORYhttps://security.netapp.com/advisory/ntap-20220107-0005/
ADVISORYhttps://www.debian.org/security/2022/dsa-5043
ADVISORYhttps://github.com/lxml/lxml/security/advisories/GHSA-55x5-fj6c-h6m8
ADVISORYhttps://lists.debian.org/debian-lts-announce/2021/12/msg00037.html
ADVISORYhttps://security.gentoo.org/glsa/202208-06
ADVISORYhttps://security.netapp.com/advisory/ntap-20220107-0005/
ADVISORYhttps://www.debian.org/security/2022/dsa-5043

All References (28)

→
https://github.com/lxml/lxml/commit/12fa9669007180a7bb87d990c375cf91ca5b664aPatch · Third Party Advisory
→
https://github.com/lxml/lxml/commit/a3eacbc0dcf1de1c822ec29fb7d090a4b1712a9c#diff-59130575b4fb2932c957db2922977d7d89afb0b2085357db1a14615a2fcad776Patch · Third Party Advisory
→
https://github.com/lxml/lxml/commit/f2330237440df7e8f39c3ad1b1aa8852be3b27c0Patch · Third Party Advisory
→
https://github.com/lxml/lxml/security/advisories/GHSA-55x5-fj6c-h6m8Third Party Advisory
→
https://lists.debian.org/debian-lts-announce/2021/12/msg00037.htmlMailing List · Third Party Advisory
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TUIS2KE3HZ2AAQKXFLTJFZPP2IFHJTC7/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/V2XMOM5PFT6U5AAXY6EFNT5JZCKKHK2V/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WZGNET2A4WGLSUXLBFYKNC5PXHQMI3I7/
→
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZQ4SPKJX3RRJK4UWA6FXCRHD2TVRQI44/
→
https://security.gentoo.org/glsa/202208-06Third Party Advisory
→
https://security.netapp.com/advisory/ntap-20220107-0005/Third Party Advisory
→
https://www.debian.org/security/2022/dsa-5043Third Party Advisory
→
https://www.oracle.com/security-alerts/cpuapr2022.htmlPatch · Third Party Advisory
→
https://www.oracle.com/security-alerts/cpujul2022.htmlPatch · Third Party Advisory
→
https://github.com/lxml/lxml/commit/12fa9669007180a7bb87d990c375cf91ca5b664aPatch · Third Party Advisory

Quick Facts

CVE IDCVE-2021-43818
CVSS Score7.1 / 10
SeverityHIGH
WeaknessCWE-74
CISA KEVNo
Affected5 vendor(s)
PublishedDec 13, 2021

Related CVEs (CWE-74)

CVE-2023-32314
10.0
CVE-2024-38366
10.0
CVE-2020-26282
10.0
CVE-2026-56699
10.0
CVE-2023-30547
10.0
CVE-2026-44182
10.0

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-43818 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWatch. CVE data is provided under the NVD usage policy.
← All Vulnerabilities·Search for CVE-2021-43818·NVD