Overleaf is a web-based collaborative LaTeX editor. Overleaf Community Edition and Server Pro prior to version 5.0.7 (or 4.2.7 for the 4.x series) contain a vulnerability that allows an arbitrary language parameter in client spelling requests to be passed to the `aspell` executable running on the server. This causes `aspell` to attempt to load a dictionary file with an arbitrary filename. File access is limited to the scope of the overleaf server. The problem is patched in versions 5.0.7 and 4.2.7. Previous versions can be upgraded using the Overleaf toolkit `bin/upgrade` command. Users unable to upgrade may block POST requests to `/spelling/check` via a Web Application Firewall will prevent access to the vulnerable spell check feature. However, upgrading is advised.
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.