Grist: XSS through unsafe value interpolation in server-rendered pages

Grist is spreadsheet software using Python as its formula language. Prior to 1.7.15, several server-rendered Grist pages embedded user-controlled values into the page and into inline scripts without fully escaping them, allowing cross-site scripting. On the main application page, a document's name or description, set by a document editor, is rendered into the page that other users load when opening the document. On the OAuth2 end-of-flow page, the openerOrigin request parameter was reflected back into the served page. Injected script runs in the victim's Grist origin and can act through the authenticated session, reading or modifying data and changing sharing settings and access rules. A document editor could therefore escalate to owner-level access. This issue is fixed in version 1.7.15.