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Remove feed from the default allowed protocols - #304
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The feed URI scheme was never accepted as a standard protocol and no major browser supports it. Removing this rarely-used scheme reduces attack surface in non-browser contexts (webviews, email clients) where legacy handlers may process nested URIs. https://en.wikipedia.org/wiki/Feed_URI_scheme
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What problem is this PR intended to solve?
Loofah's default safelist allows the
feed:URI scheme. The feed URI scheme was never accepted as a standard protocol, and no major browser supports it. Keeping it in the default allowlist creates a potential protocol smuggling vector in non-browser contexts such as webviews and email clients, where legacy handlers may process a URI nested after the scheme.This PR removes
feedfromACCEPTABLE_PROTOCOLSand adds a test asserting thatfeed:URIs are scrubbed.Applications that rely on
feed:links can restore the previous behavior by adding the scheme back to the safelist:Please note that this change hardens Loofah, but there is no known exploit that uses
feed:and so it does not reach the threshold for a security advisory.Thanks to hackerone researcher mk_security for raising this issue in a responsible manner.