fix(api): reject path traversal in external subtitle filename - #1385
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revam merged 4 commits intoJul 27, 2026
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Foowy
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Purely security check, most users will not see this, but we might as well not be a weak point |
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Used a 250ms match timeout for |
Foowy
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July 18, 2026 18:58
…s-control bypass `GetExternalSubtitle` passed the raw `filename` route parameter into `Path.Combine` with no traversal or absolute-path check, allowing an authenticated (or anonymous, if `AllowAnonymousFileStreamingInAPIv3` is enabled) caller to read arbitrary files on the host via `../` sequences or a rooted path. Reject any `filename` containing `/`, `\`, or equal to `.`/`..` before combining paths. `GetFileStreamInternal`, `GetFileStreamDirectory`, and `GetExternalSubtitle` also had no `AllowedSeries` check, unlike other endpoints in this controller — a restricted/parental-control user account could stream video or subtitles for series outside their allowed list. Added `IsSeriesAllowedForFile`, reusing the existing `JMMUser.AllowedSeries` check.
…versal fix only Scoped this PR down to the path-traversal fix in GetExternalSubtitle. The AllowedSeries check only matters for installs using Shoko's restricted/parental-control user profiles and isn't worth bundling with the traversal fix.
…tles The previous check rejected any `filename` containing `/` or `\`, which also blocked legitimate subtitles living in a subfolder next to the video, while doing nothing to stop encoded traversal segments embedded elsewhere in the name. Replaced with a regex that rejects `.` /`..` path segments specifically (`PathTraversalPattern`), and added a whitelist check against the video's known external subtitle filenames (`MediaInfo.TextStreams`) so `filename` can only resolve to a subtitle actually linked to the file.
SonarCloud flagged the unbounded Regex constructor as a ReDoS risk. 250ms matches the timeout convention already used by LogService's filter regex.
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Summary
GetExternalSubtitle(FileController) passed the rawfilenameroute parameter straight intoPath.Combinewith no traversal/absolute-path check — an authenticated caller (or anonymous, ifAllowAnonymousFileStreamingInAPIv3is on) could read arbitrary files on the host via../sequences or a rooted path.filenamecontaining/or\— but that also blocked legitimate subtitles living in a subfolder next to the video, while doing nothing to stop encoded traversal segments embedded elsewhere in the name. Replaced with a regex (PathTraversalPattern) that specifically rejects./..path segments, plus a whitelist check against the video's actual known external subtitle filenames (MediaInfo.TextStreams) —filenamecan now only ever resolve to a subtitle genuinely linked to that file, not just any traversal-free string.LogService's filter regex.AllowedSeries(restricted/parental-control profile) check to the file-streaming endpoints, since they were missing it unlike other endpoints in this controller — that was dropped to keep this PR scoped to the traversal fix only; it's a separate, lower-severity gap that can be addressed independently.Found during a local security review of the file-streaming surface.
Test plan
dotnet build Shoko.Server.sln -c Release— 0 errorsRebase history
master@a9126a417(4 commits), now at1f7d99355