CVE-2026-41066

HighPublic PoC

Published: 24 April 2026

Published

24 April 2026

Modified

27 April 2026

KEV Added

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Patch

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CVSS Score 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS Score 0.0004 12.3th percentile

Risk Priority 15 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-41066 is a high-severity Improper Restriction of XML External Entity Reference (CWE-611) vulnerability in Lxml Lxml. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 12.3th 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 are NIST 800-53 CM-6 (Configuration Settings) and SI-10 (Information Input Validation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190) and 1 other technique. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-10 Information Input Validation good match

prevent

Requires validation of untrusted XML inputs to prevent external entity expansion that enables local file reads via XXE.

CM-6 Configuration Settings good match

prevent

Mandates secure configuration settings for lxml parsers, such as resolve_entities=False, to disable local file access from untrusted XML.

SI-2 Flaw Remediation good match

prevent

Directly addresses remediation of the lxml XXE flaw by identifying, patching to version 6.1.0, and verifying updates.

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 →

T1005 Data from Local System Collection

Adversaries may search local system sources, such as file systems, configuration files, local databases, virtual machine files, or process memory, to find files of interest and sensitive data prior to Exfiltration.

attack.mitre.org →

Why these techniques?

XXE vulnerability enables remote unauthenticated exploitation of applications accepting XML input (T1190) to read arbitrary local files (T1005).

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD Description

lxml is a library for processing XML and HTML in the Python language. Prior to 6.1.0, using either of the two parsers in the default configuration (with resolve_entities=True) allows untrusted XML input to read local files. Setting the resolve_entities option…

explicitly to resolve_entities='internal' or resolve_entities=False disables the local file access. This vulnerability is fixed in 6.1.0.

Deeper analysisAI

CVE-2026-41066 is an XML External Entity (XXE) vulnerability, classified as CWE-611, in the lxml library for processing XML and HTML in Python. Versions prior to 6.1.0, when using either parser in the default configuration with resolve_entities=True, allow untrusted XML input to read local files. The issue carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N) and was published on 2026-04-24.

Remote, unauthenticated attackers can exploit this vulnerability by providing malicious XML input to applications that process it using lxml's default parser settings. Exploitation requires network access and low complexity, enabling attackers to achieve high confidentiality impact by reading arbitrary local files on the targeted system.

The vulnerability is addressed in lxml 6.1.0. Mitigation involves explicitly setting resolve_entities='internal' or resolve_entities=False to disable local file access. Additional details are available in the Launchpad bug report at https://bugs.launchpad.net/lxml/+bug/2146291 and the GitHub security advisory at https://github.com/lxml/lxml/security/advisories/GHSA-vfmq-68hx-4jfw.