Drupal addressed CVE-2020

Arbitrary PHP code execution vulnerability in Drupal Core under certain circumstances. An attacker could trick an administrator into visiting a malicious site that could result in creating a carefully named directory on the file system. With this directory in place, an attacker could attempt to brute force a remote code execution vulnerability. Windows servers are most likely to be affected. This issue affects: Drupal Drupal Core 8.8.x versions prior to 8.8.8; 8.9.x versions prior to 8.9.1; 9.0.1 versions prior to 9.0.1.

CVE-2020-13671 is a file-upload flaw in Drupal core: improper sanitization of uploaded file names and their extensions allows a submitted file to bypass the allowed-extension checks (CWE-434, Unrestricted Upload of File with Dangerous Type). It is triggered when a user with upload privileges submits a crafted file name (for example, one carrying a dangerous or double extension) through any Drupal form or API path that stores uploaded files. An attacker gains the ability to plant arbitrary files on the server, and on sites where the web server executes uploaded files this can escalate to full remote code execution and site compromise. Any site running an affected release of Drupal core is exposed; the provided data lists 'Drupal core' as the affected product without enumerating version ranges. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2022-01-18, confirming exploitation in the wild (ransomware use unknown), and EPSS assigns a 35.4% probability of exploitation within 30 days.

Do: Update Drupal core to the patched release specified in the vendor's security advisory (CISA required action: apply updates per vendor instructions). Until patched, restrict which roles can upload files, enforce strict allowed-extension lists, and ensure the public upload directory is configured so the web server does not execute uploaded files as scripts. Given the KEV listing, inspect upload directories and web logs for unexpected files or web shells.