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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-41066: 0.32% estimated exploitation activity in the next 30 days; percentile 25.56 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Using either of the two parsers in the default configuration (with resolveentities=True) allows untrusted XML input to read local files. Patches lxml 6.1.0 changes the default to resolveentities='internal', thus disallowing local file access by default. Workarounds Setting the resolveentities option explicitly to resolveentities='internal' or resolveentities=False disables the local file access. Resources Original report: https://bugs.launchpad.net/lxml/+bug/2146291 The default option was changed to resolveentities='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.

Published by the source

21 Apr 2026, 20:38 UTC

Last modified by the source

10 Sep 2026, 03:51 UTC

Source last checked

26 Oct 2026, 13:44 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-vfmq-68hx-4jfw

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-vfmq-68hx-4jfw

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# Patch Next advisory brief: CVE-2026-41066

Advisory: lxml: Default configuration of iterparse() and ETCompatXMLParser() allows XXE to local files
IDs: CVE-2026-41066, GHSA-vfmq-68hx-4jfw
Record: https://patchnext.com/advisories/cve-2026-41066 (revision 2, source checked 26 Oct 2026, 13:44 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: lxml 6.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI lxml: affected < 6.1.0; fixed in 6.1.0

## Suggested inspection (read-only)
- `python -m pip show lxml`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on lxml.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-vfmq-68hx-4jfw (OSV record GHSA-vfmq-68hx-4jfw lists affected ranges: PyPI lxml >=0 <6.1.0 (fixed))
- Verified: https://github.com/advisories/GHSA-vfmq-68hx-4jfw (GitHub-reviewed advisory GHSA-vfmq-68hx-4jfw lists affected ranges: PyPI lxml >=0 <6.1.0)

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