Update TAR guidance for untrusted archives#54670
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…ributes Adds security guidance to the ZIP/TAR best-practices article for handling untrusted TAR archives: - A note that destination boundary validation assumes the destination is a real directory the app controls; a junction/symlink destination (or parent) causes extraction to follow the link, even with TarFile.ExtractToDirectory. - A new section on PAX extended attributes and link names as untrusted, archive-supplied input that can override header fields. - Updated the untrusted-metadata checklist item to include link names and PAX extended attributes. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
mangod9
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Pull request overview
Updates the archive security best-practices guidance to cover TAR-specific risks when extracting untrusted archives, complementing the existing ZIP guidance.
Changes:
- Adds a note clarifying the limits of destination boundary validation when the destination path contains junctions or symlinks.
- Documents TAR PAX extended attributes and TAR link names as untrusted metadata that requires validation and limits.
- Updates the best-practices checklist to explicitly include TAR link names and PAX extended attributes.
gewarren
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Jul 8, 2026
Co-authored-by: Genevieve Warren <24882762+gewarren@users.noreply.github.com>
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@copilot can you please apply the review suggested text changes? |
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
GrabYourPitchforks
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Jul 8, 2026
| - The trailing directory separator on `fullDestDir` is critical—without it, a path like `/safe-dir-evil/file` would incorrectly match `/safe-dir`. | ||
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| > [!NOTE] | ||
| > Boundary validation assumes the destination directory itself is a real directory you control. If the destination directory or one of its parents is already a junction or symbolic link, extraction follows that link and writes to the link's target—even with <xref:System.Formats.Tar.TarFile.ExtractToDirectory*?displayProperty=nameWithType>, which otherwise rejects entries and link targets that escape the destination. When handling untrusted archives, extract into a fresh, application-controlled directory rather than a reused or externally writable location. |
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When handling untrusted archives, extract into a fresh, application-controlled directory rather than a reused or externally writable location.
This is inconsistent with line 44 in this same document, which says that ExtractToDirectory is meant only for trusted archives.
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updated the content to not include ExtractToDirectory
…chive note The note lives in the streaming/untrusted-input section, but referenced TarFile.ExtractToDirectory, which the article frames as a trusted-input convenience API. Reword to keep the note focused on manual boundary validation and avoid the inconsistency. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Updating the ZIP/TAR best-practices docs with security guidance for TAR API use: destination boundary validation, PAX extended attributes, and link names.
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