How severe is CVE-2021-43818?

CVE-2021-43818 has a CVSS 3.x base score of 8.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity high, and availability none.

Is CVE-2021-43818 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (82nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-43818?

CVE-2021-43818 primarily affects Lxml. In total, 15 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-43818?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-43818 published?

CVE-2021-43818 was published on 2021-12-13 and last updated on 2026-06-17.

CVE-2021-43818

CVE-2021-43818 is a high-severity vulnerability in Lxml with a CVSS 3.x base score of 8.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: High (CVSS 3.x base score 8.2)
CVSS v2: 6.8
EPSS exploit prediction: 2% (82nd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Lxml
Published: 2021-12-13
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-43818?: 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.
How severe is CVE-2021-43818?: CVE-2021-43818 has a CVSS 3.x base score of 8.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity high, and availability none.
Is CVE-2021-43818 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (82nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-43818?: CVE-2021-43818 primarily affects Lxml. In total, 15 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-43818?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-43818 published?: CVE-2021-43818 was published on 2021-12-13 and last updated on 2026-06-17.

References

Affected products (15)

cpe:2.3:a:lxml:lxml:*:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
cpe:2.3:a:netapp:solidfire:-:*:*:*:*:*:*:*
cpe:2.3:a:netapp:solidfire_enterprise_sds:-:*:*:*:*:*:*:*
cpe:2.3:o:netapp:hci_storage_node_firmware:-:*:*:*:*:*:*:*
cpe:2.3:a:oracle:communications_cloud_native_core_binding_support_function:22.1.3:*:*:*:*:*:*:*
cpe:2.3:a:oracle:communications_cloud_native_core_network_exposure_function:22.1.1:*:*:*:*:*:*:*
cpe:2.3:a:oracle:communications_cloud_native_core_policy:22.2.0:*:*:*:*:*:*:*
cpe:2.3:a:oracle:http_server:12.2.1.3.0:*:*:*:*:*:*:*
cpe:2.3:a:oracle:http_server:12.2.1.4.0:*:*:*:*:*:*:*
cpe:2.3:a:oracle:zfs_storage_appliance_kit:8.8:*:*:*:*:*:*:*

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