Redmine before 4.2.11 and 5.0.x before 5.0.6 allows XSS via thumbnails.

Redmine before 4.2.11 and 5.0.x before 5.0.6 allows XSS in the Textile formatter.

Redmine before 4.2.11 and 5.0.x before 5.0.6 allows XSS in a Markdown formatter.

Redmine before 4.2.9 and 5.0.x before 5.0.4 allows persistent XSS in its Textile formatter due to improper sanitization in Redcloth3 Textile-formatted fields. Depending on the configuration, this may require login as a registered user.

Redmine before 4.2.9 and 5.0.x before 5.0.4 allows persistent XSS in its Textile formatter due to improper sanitization of the blockquote syntax in Textile-formatted fields.

Redmine 5.x before 5.0.4 allows downloading of file attachments of any Issue or any Wiki page due to insufficient permission checks. Depending on the configuration, this may require login as a registered user.

Redmine before 4.1.5 and 4.2.x before 4.2.3 may disclose the names of users on activity views due to an insufficient access filter.

Redmine 4.2.0 and 4.2.1 allow existing user sessions to continue upon enabling two-factor authentication for the user's account, but the intended behavior is for those sessions to be terminated.

Redmine before 4.0.9 and 4.1.x before 4.1.3 allows an attacker to learn the values of internal authentication keys by observing timing differences in string comparison operations within SysController and MailHandlerController.

Redmine before 4.0.9, 4.1.x before 4.1.3, and 4.2.x before 4.2.1 allows users to circumvent the allowed filename extensions of uploaded attachments.