CVE-2021-28957 (GCVE-0-2021-28957)

Vulnerability from cvelistv5 – Published: 2021-03-21 04:39 – Updated: 2025-12-17 21:31
VLAI
Summary
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.
Severity
6.1 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • n/a
  • CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Assigner
References
Show details on NVD website
To clipboard 

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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-06-28T07:45:17+00:00",
      "cve": "CVE-2021-28957",
      "id": "CVE-2021-28957",
      "initial_release_date": "2021-03-21T00:00:00+00:00",
      "product_status:fixed": "871",
      "product_status:known_affected": "7",
      "product_status:known_not_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "python-lxml: Missing input sanitization for formaction HTML5 attributes may lead to XSS",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2021/cve-2021-28957.json",
      "version": "3"
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  }
}



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Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.