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lxml: Default configuration of iterparse() and ETCompatXMLParser() allows XXE to local files

High severity GitHub Reviewed Published Apr 18, 2026 in lxml/lxml • Updated Apr 21, 2026

Package

pip lxml (pip)

Affected versions

< 6.1.0

Patched versions

6.1.0

Description

Impact

Using either of the two parsers in the default configuration (with resolve_entities=True) allows untrusted XML input to read local files.

Patches

lxml 6.1.0 changes the default to resolve_entities='internal', thus disallowing local file access by default.

Workarounds

Setting the resolve_entities option explicitly to resolve_entities='internal' or resolve_entities=False disables the local file access.

Resources

Original report: https://bugs.launchpad.net/lxml/+bug/2146291

The default option was changed to resolve_entities='internal' for the normal XML and HTML parsers in lxml 5.0. The default was not changed for iterparse() and ETCompatXMLParser() at the time. lxml 6.1 makes the safe option the default for all parsers.

References

@scoder scoder published to lxml/lxml Apr 18, 2026
Published to the GitHub Advisory Database Apr 21, 2026
Reviewed Apr 21, 2026
Last updated Apr 21, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(9th percentile)

Weaknesses

Improper Restriction of XML External Entity Reference

The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output. Learn more on MITRE.

CVE ID

CVE-2026-41066

GHSA ID

GHSA-vfmq-68hx-4jfw

Source code

Credits

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