Cyber Resilience

CVE-2026-28348

Fedoralovespython Lxml Html Clean ≤ 0.4.4

Public PoC
Published
05 March 2026
Modified
09 March 2026
Patch / advisory
View advisory
CVSS Score v3.1 6.1
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS Score 0.0023 14th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2026-28348 is a medium-severity Improper Encoding or Escaping of Output (CWE-116) vulnerability in Fedoralovespython Lxml Html Clean. Its CVSS base score is 6.1 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 14th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) and SI-2 (Flaw Remediation) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A05:2025 Injection

EU & UK References

Vulnerability Data

lxml_html_clean is a project for HTML cleaning functionalities copied from `lxml.html.clean`. Prior to version 0.4.4, the _has_sneaky_javascript() method strips backslashes before checking for dangerous CSS keywords. This causes CSS Unicode escape sequences to bypass the @import and expression() filters, allowing…

more

external CSS loading or XSS in older browsers. This issue has been patched in version 0.4.4.

CWE(s)
CWE-116

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
Why these techniques?

Sanitization bypass in HTML cleaner enables XSS/external CSS injection, directly facilitating exploitation of public-facing web apps and client-side code execution.

Confidence: MEDIUM · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-28350Same product: Fedoralovespython Lxml Html Clean
CVE-2024-52595Same product: Fedoralovespython Lxml Html Clean
CVE-2026-46628Shared CWE-116
CVE-2026-24439Shared CWE-116
CVE-2026-54893Shared CWE-116
CVE-2024-10441Shared CWE-116
CVE-2026-34483Shared CWE-116
CVE-2025-59936Shared CWE-116
CVE-2026-48358Shared CWE-116
CVE-2026-56379Shared CWE-116

Affected Assets

fedoralovespython
lxml html clean
≤ 0.4.4

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • SI-10 Information Input Validation
  • SI-2 Flaw Remediation
Detect
Catch it (NIST detect / respond)
  • RA-5 Vulnerability Monitoring and Scanning
Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.1.2
  • V1.2.1
  • V1.2.3

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match
prevent

Directly requires validation and sanitization of inputs (including CSS/JS constructs) to reject malformed or escaped payloads that bypass filters, addressing the root CWE-116 flaw in _has_sneaky_javascript().

SI-2 Flaw Remediation good match
prevent

Mandates prompt application of patches to remediate known flaws such as the backslash-stripping bypass fixed in lxml_html_clean 0.4.4.

RA-5 Vulnerability Monitoring and Scanning partial match
detect

Requires ongoing vulnerability scanning to identify use of the vulnerable lxml_html_clean version before exploitation of the CSS Unicode escape bypass.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require proper output encoding to prevent injection and message malformation.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.28 Secure coding mostly match
prevents

Secure coding standards explicitly require correct output encoding and escaping to preserve message structure.

A.8.29 Security testing in development and acceptance mostly match
detects

Security testing can detect missing or incorrect encoding but does not itself implement the control.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle mandates output encoding/escaping practices that directly prevent improper encoding.

A.8.26 Application security requirements partial match
prevents

Application security requirements include explicit rules for safe output handling and encoding.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles reduce the likelihood of missing encoding but do not prescribe the actual technique.

References