OpenProject is open-source, web-based project management software. In versions prior to 11.3.3, the `MessagesController` class of OpenProject has a `quote` method that implements the logic behind the Quote button in the discussion forums, and it uses a regex to strip `

` tags from the message being quoted. The `(.|s)` part can match a space character in two ways, so an unterminated `

` tag containing `n` spaces causes Ruby's regex engine to backtrack to try 2n states in the NFA. This will result in a Regular Expression Denial of Service. The issue is fixed in OpenProject 11.3.3. As a workaround, one may install the patch manually.

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