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February 12, 2021

GHSL-2020-199: Open redirect vulnerability in Slashify - CVE-2021-3189

GitHub Security Lab

Coordinated Disclosure Timeline


Open redirect in Slashify


The slashify npm package.

Tested Version

Latest commit at the date of reporting.


The package is an Express middleware that normalises routes by stripping any final slash, redirecting, for example, bookings/latest/ to bookings/latest. However, it does not validate the path it redirects to in any way. In particular, if the path starts with two slashes (or two backslashes, or a slash and a backslash, etc.) it may redirect to a different domain.

Consider the example from the docs. Assume we have run it and started a server on localhost:3000, then visiting localhost:3000/// redirects you to


Open redirect



This issue was discovered and reported by GitHub team member @max-schaefer (Max Schaefer).


You can contact the GHSL team at, please include GHSL-2020-199 in any communication regarding this issue.