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Exploited. On CISA's list since 2022-01-18.
CVE-2020-13671 · Drupal Drupal core · Published 2020-11-20
8.8 out of 10
CVSS rates it high.
36%
Estimated chance of exploitation in the next 30 days, higher than 98% of all scored flaws (EPSS, 2026-10-29).
Yes
CISA has seen it exploited in real attacks. For US government agencies the fix is deadline passed 1565 days ago (2022-07-18).
Apply updates per vendor instructions.
Improper sanitization in the extension file names is present in Drupal core.
Drupal core does not properly sanitize certain filenames on uploaded files, which can lead to files being interpreted as the incorrect extension and served as the wrong MIME type or executed as PHP for certain hosting configurations. This issue affects: Drupal Drupal Core 9.0 versions prior to 9.0.8, 8.9 versions prior to 8.9.9, 8.8 versions prior to 8.8.11, and 7 versions prior to 7.74.
From the NVD.
Explore this week’s weaknesses and all learning topics
Understand the kind of weakness behind this flaw. These resources teach the weakness, rather than reproduce this specific CVE. Follow the vendor's advice above to fix the affected product.
An application accepts a dangerous file type that can later be executed or served unsafely.
CWE-434 · CISA KEV; NVD record: 134c704f-9b21-4f2e-91b3-4a467353bcc0; NVD record: nvd@nist.gov
Reading and practice labs · Free account for labs. Basic HTTP knowledge; some labs use Burp Suite.
CWE is a catalogue of weakness types. Labels come from the sources shown and can differ or change. Resource matches reviewed 16 October 2026.
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Exploited flaws from CISA's KEV catalogue. Chance of exploitation from EPSS by FIRST. Descriptions and scores from the NVD. This product uses the NVD API but is not endorsed or certified by the NVD.