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Not in CISA KEV
MEDIUM severity

CVE-2017-6921 — core

MEDIUM

CVE-2017-6921 is a medium-severity (CVSS 5.9) Improper Input Validation vulnerability in drupal/core. A fix is available for drupal/core — see the affected versions and patch details below.

Drupal file REST resource does not properly validate

Also known asGHSA-h377-287m-w2r9
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs79th percentile — riskier than 79% of all scored CVEsHighest risk
0.00%0.78%1.56%2.33%0.4%1.8%May 26Sep 26Nov 26

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

2 pkgs affected
🐘drupal/core🐘drupal/drupal

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

Description

In Drupal 8 prior to 8.3.4; The file REST resource does not properly validate some fields when manipulating files. A site is only affected by this if the site has the RESTful Web Services (rest) module enabled, the file REST resource is enabled and allows PATCH requests, and an attacker can get or register a user account on the site with permissions to upload files and to modify the file resource.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistdrupal/core≥ 8.0&&< 8.3.48.3.4composer require drupal/core:^8.3.4
🐘Packagistdrupal/drupal≥ 8.0&&< 8.3.48.3.4composer require drupal/drupal:^8.3.4

Affected Products

1 product · 1 configurations
Application
drupaldrupal
≥ 8.0.0 && < 8.3.4
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update drupal/core to 8.3.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2017-6921 is resolved across your whole dependency graph.

  3. 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.

Frequently Asked Questions

In Drupal 8 prior to 8.3.4; The file REST resource does not properly validate some fields when manipulating files. A site is only affected by this if the site has the RESTful Web Services (rest) module enabled, the file REST resource is enabled and allows PATCH requests, and an attacker can get or register a user account on the site with permissions to upload files and to modify the file resource.
O3 Security · Impact-Aware SCA

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CVE-2017-6921: core — Fixed in 8.3.4