CVE-2021-28957

Lxml vulnerability

CVSS

6.1

EPSS

4.0%

EPSS pct

89th

Exploited

No known

An XSS vulnerability was discovered in python-lxml's clean module versions before 4.6.3. When disabling the safe_attrs_only and forms arguments, the Cleaner class does not remove the formaction attribute allowing for JS to bypass the sanitizer. A remote attacker could exploit this flaw to run arbitrary JS code on users who interact with incorrectly sanitized HTML. This issue is patched in lxml 4.6.3.

Affected vendor

Lxml

Affected product

Lxml

CVSS vector

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

Weakness type (CWE)

CWE-79 — Cross-Site Scripting (XSS)

Published

2021-03-21

Risk analysis

Based on its CVSS vector, this vulnerability is exploitable over the network, low attack complexity, requiring no privileges, user interaction. Successful exploitation leads to low impact to confidentiality, low impact to integrity.

Its EPSS score of 4.0% reflects a lower probability of exploitation activity in the wild over the next 30 days, placing it above 89% of all scored CVEs.

Check your external exposure to CVE-2021-28957

Confirm whether Lxml Lxml is running on any internet-facing host or subdomain.
Match discovered service fingerprints against the version affected by CVE-2021-28957.
Prioritise remediation if the asset is public, business-critical, or near authentication/payment flows.

How ThreatPort helps with CVE-2021-28957

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