fix: consider about:blank a safe URL - #25317
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The safe URL check is based on the URL scheme and the about scheme is not safe by default, which also blocked legitimate use of about:blank, for example as the initial source of an IFrame. Accept about:blank regardless of the configured schemes since it shows an empty document and cannot run scripts. Other about: URLs are still checked against the configured schemes. Fixes #25316
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This PR cherry-picks changes from the original PR #25317 to branch 25.2. --- #### Original PR description > The safe URL check is based on the URL scheme, and `about` is not in the default set of safe schemes. As a side effect, this also blocked legitimate uses of `about:blank`, such as setting it as the initial source of an `IFrame`. > > `about:blank` is now accepted regardless of the configured safe schemes, since it renders an empty document and cannot run scripts. The comparison is case-insensitive, so `About:Blank` is treated the same way. > > Other `about:` URLs (e.g. `about:config`, or lookalikes such as `about:blank:evil`) are unchanged: they are still rejected unless the `about` scheme is explicitly configured as safe via the `safeUrlSchemes` init parameter. > > ### Changes > > - `UrlUtil.isSafeUrl(...)` short-circuits to `true` for a trimmed, case-insensitive match on `about:blank`, before the scheme-based check. > - Javadoc updated on `UrlUtil.isSafeUrl`, `Constants.DEFAULT_URL_SAFE_SCHEMES` and `InitParameters.URL_SAFE_SCHEMES` to document the exception. > - New tests in `UrlUtilTest` covering `about:blank` (default schemes, mixed case, and a scheme set that excludes `about`) and the other `about:` URLs that must stay unsafe. > > Fixes #25316 Co-authored-by: totally-not-ai[bot] <290682512+totally-not-ai[bot]@users.noreply.github.com>
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The safe URL check is based on the URL scheme, and
aboutis not in the default set of safe schemes. As a side effect, this also blocked legitimate uses ofabout:blank, such as setting it as the initial source of anIFrame.about:blankis now accepted regardless of the configured safe schemes, since it renders an empty document and cannot run scripts. The comparison is case-insensitive, soAbout:Blankis treated the same way.Other
about:URLs (e.g.about:config, or lookalikes such asabout:blank:evil) are unchanged: they are still rejected unless theaboutscheme is explicitly configured as safe via thesafeUrlSchemesinit parameter.Changes
UrlUtil.isSafeUrl(...)short-circuits totruefor a trimmed, case-insensitive match onabout:blank, before the scheme-based check.UrlUtil.isSafeUrl,Constants.DEFAULT_URL_SAFE_SCHEMESandInitParameters.URL_SAFE_SCHEMESto document the exception.UrlUtilTestcoveringabout:blank(default schemes, mixed case, and a scheme set that excludesabout) and the otherabout:URLs that must stay unsafe.Fixes #25316