Under certain circumstances, the Drupal core form API evaluates form element access incorrectly. This may lead to a user being able to alter data they should not have access to. No forms provided by Drupal core are known to be vulnerable. However, forms added through contributed or custom modules or themes may be affected.

Drupal core sanitizes filenames with dangerous extensions upon upload (reference: SA-CORE-2020-012) and strips leading and trailing dots from filenames to prevent uploading server configuration files (reference: SA-CORE-2019-010). However, the protections for these two vulnerabilities previously did not work correctly together. As a result, if the site were configured to allow the upload of files with an htaccess extension, these files' filenames would not be properly sanitized. This could allow bypassing the protections provided by Drupal core's default .htaccess files and possible remote code execution on Apache web servers. This issue is mitigated by the fact that it requires a field administrator to explicitly configure a file field to allow htaccess as an extension (a restricted permission), or a contributed module or custom code that overrides allowed file uploads.

In some situations, the Image module does not correctly check access to image files not stored in the standard public files directory when generating derivative images using the image styles system. Access to a non-public file is checked only if it is stored in the "private" file system. However, some contributed modules provide additional file systems, or schemes, which may lead to this vulnerability. This vulnerability is mitigated by the fact that it only applies when the site sets (Drupal 9) $config['image.settings']['allow_insecure_derivatives'] or (Drupal 7) $conf['image_allow_insecure_derivatives'] to TRUE. The recommended and default setting is FALSE, and Drupal core does not provide a way to change that in the admin UI. Some sites may require configuration changes following this security release. Review the release notes for your Drupal version if you have issues accessing files or image styles after updating.

Drupal core's form API has a vulnerability where certain contributed or custom modules' forms may be vulnerable to improper input validation. This could allow an attacker to inject disallowed values or overwrite data. Affected forms are uncommon, but in certain cases an attacker could alter critical or sensitive data.

Twig is a template language for PHP. Versions 1.x prior to 1.44.7, 2.x prior to 2.15.3, and 3.x prior to 3.4.3 encounter an issue when the filesystem loader loads templates for which the name is a user input. It is possible to use the `source` or `include` statement to read arbitrary files from outside the templates' directory when using a namespace like `@somewhere/../some.file`. In such a case, validation is bypassed. Versions 1.44.7, 2.15.3, and 3.4.3 contain a fix for validation of such template names. There are no known workarounds aside from upgrading.

guzzlehttp/psr7 is a PSR-7 HTTP message library. Versions prior to 1.8.4 and 2.1.1 are vulnerable to improper header parsing. An attacker could sneak in a new line character and pass untrusted values. The issue is patched in 1.8.4 and 2.1.1. There are currently no known workarounds.

CKEditor4 is an open source what-you-see-is-what-you-get HTML editor. CKEditor4 prior to version 4.18.0 contains a vulnerability in the `dialog` plugin. The vulnerability allows abuse of a dialog input validator regular expression, which can cause a significant performance drop resulting in a browser tab freeze. A patch is available in version 4.18.0. There are currently no known workarounds.

CKEditor4 is an open source what-you-see-is-what-you-get HTML editor. A vulnerability has been discovered in the core HTML processing module and may affect all plugins used by CKEditor 4 prior to version 4.18.0. The vulnerability allows someone to inject malformed HTML bypassing content sanitization, which could result in executing JavaScript code. This problem has been patched in version 4.18.0. There are currently no known workarounds.

Under some circumstances, the Drupal core JSON:API module does not properly restrict access to certain content, which may result in unintended access bypass. Sites that do not have the JSON:API module enabled are not affected.

Drupal's JSON:API and REST/File modules allow file uploads through their HTTP APIs. The modules do not correctly run all file validation, which causes an access bypass vulnerability. An attacker might be able to upload files that bypass the file validation process implemented by modules on the site.

Archive_Tar through 1.4.10 has :// filename sanitization only to address phar attacks, and thus any other stream-wrapper attack (such as file:// to overwrite files) can still succeed.

Archive_Tar through 1.4.10 allows an unserialization attack because phar: is blocked but PHAR: is not blocked.

In Drupal 8.x prior to 8.3.7 When creating a view, you can optionally use Ajax to update the displayed data via filter parameters. The views subsystem/module did not restrict access to the Ajax endpoint to only views configured to use Ajax. This is mitigated if you have access restrictions on the view. It is best practice to always include some form of access restrictions on all views, even if you are using another module to display them.

In Drupal core 8.x prior to 8.3.4 and Drupal core 7.x prior to 7.56; Private files that have been uploaded by an anonymous user but not permanently attached to content on the site should only be visible to the anonymous user that uploaded them, rather than all anonymous users. Drupal core did not previously provide this protection, allowing an access bypass vulnerability to occur. This issue is mitigated by the fact that in order to be affected, the site must allow anonymous users to upload files into a private file system.

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.

In Drupal 8 prior to 8.3.7; When using the REST API, users without the correct permission can post comments via REST that are approved even if the user does not have permission to post approved comments. This issue only affects sites that have the RESTful Web Services (rest) module enabled, the comment entity REST resource enabled, and where an attacker can access a user account on the site with permissions to post comments, or where anonymous users can post comments.

In versions of Drupal 8 core prior to 8.3.7; There is a vulnerability in the entity access system that could allow unwanted access to view, create, update, or delete entities. This only affects entities that do not use or do not have UUIDs, and entities that have different access restrictions on different revisions of the same entity.

Drupal core 8 before versions 8.3.4 allows remote attackers to execute arbitrary code due to the PECL YAML parser not handling PHP objects safely during certain operations.

An issue was discovered in Http Foundation in Symfony 2.7.0 through 2.7.48, 2.8.0 through 2.8.43, 3.3.0 through 3.3.17, 3.4.0 through 3.4.13, 4.0.0 through 4.0.13, and 4.1.0 through 4.1.2. It arises from support for a (legacy) IIS header that lets users override the path in the request URL via the X-Original-URL or X-Rewrite-URL HTTP request header. These headers are designed for IIS support, but it's not verified that the server is in fact running IIS, which means anybody who can send these requests to an application can trigger this. This affects \Symfony\Component\HttpFoundation\Request::prepareRequestUri() where X-Original-URL and X_REWRITE_URL are both used. The fix drops support for these methods so that they cannot be used as attack vectors such as web cache poisoning.

Cross-site scripting (XSS) vulnerability in the Enhanced Image (aka image2) plugin for CKEditor (in versions 4.5.10 through 4.9.1; fixed in 4.9.2), as used in Drupal 8 before 8.4.7 and 8.5.x before 8.5.2 and other products, allows remote attackers to inject arbitrary web script through a crafted IMG element.