How severe is CVE-2026-41066?

CVE-2026-41066 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-41066?

CVE-2026-41066 affects the following packages: lxml (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-41066?

Update lxml to 6.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-41066 is resolved across your whole dependency graph.

How do I detect CVE-2026-41066 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for lxml, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-41066 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-41066 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-41066 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-41066?

CVE-2026-41066 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 26th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-41066?

CVE-2026-41066 is classified as XML External Entity (XXE) (CWE-611). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-41066 published, and has it been updated?

CVE-2026-41066 was published on April 24, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

HIGH severity

CVE-2026-41066 — lxml

HIGH

CVE-2026-41066 is a high-severity (CVSS 7.5) XML External Entity (XXE) vulnerability in lxml. A fix is available for lxml — see the affected versions and patch details below.

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

Also known asGHSA-vfmq-68hx-4jfwPYSEC-2026-87

Published

Apr 24, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-41066.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs26th percentile — riskier than 26% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐍lxml

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`lxml`	all versions	6.1.0`pip install --upgrade 'lxml==6.1.0'`

Affected Products

1 product · 1 configurations

Application

lxmllxml

< 6.1.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for lxml, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update lxml to 6.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-41066 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Workaround published by Red Hat

Applications using the lxml library to process untrusted XML input should explicitly configure the parser to prevent external entity resolution. This can be achieved by setting the `resolve_entities` option to `False` or `'internal'` when initializing the parser. For example, `etree.XML(xml_input, parser=etree.XMLParser(resolve_entities=False))` or `etree.HTML(html_input, parser=etree.HTMLParser(resolve_entities='internal'))`.

Source: Red Hat security advisory for CVE-2026-41066 (CC BY 4.0)

UbuntuHIGH

USN-8897-1Ubuntu

Frequently Asked Questions

### 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