fix(asar): path traversal (zip-slip) on extract + Pickle buffer overrun#143
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AsarExtractor's path-traversal guard called Extensions.GetRelativePath, whose fast path strips the destination prefix literally without resolving ".." segments. A crafted archive entry such as "a/../../evil" produced a relative path that did not start with "..", so the guard passed and the file was written outside the extraction directory once the OS resolved the "..". The out-of-package symlink guard shared the same weakness. Add Extensions.IsPathInside, which normalises both paths with Path.GetFullPath before the containment check, and use it for both the file/directory and symlink guards. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Pickle.Resize allocated the backing array as _header.Length + newCapacity but advertised _capacityAfterHeader = newCapacity. On the first growth _header is still empty, so the array ended up _headerSize (4) bytes short of the header + capacity it claimed. A write that fills the payload then overran the buffer, throwing an ArgumentException when the serialised asar header was 4089-4092 bytes. Allocate _headerSize + newCapacity instead, matching Chromium's realloc(header_size_ + new_capacity). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Summary
Fixes two code-level bugs in the
AsarSharppack/extract pipeline found by source audit (full write-ups and reproductions in #142).1.
AsarSharp/AsarExtractor.cs— path traversal / zip-slip (major)The extraction guard used
Extensions.GetRelativePath, whose fast path strips thedestprefix without resolving.., so a crafted entry likea/../../evilbypassed the check and was written outsidedest. The out-of-package symlink guard shared the weakness.Extensions.IsPathInside, which normalises both paths withPath.GetFullPathbefore the containment check.2.
AsarSharp/PickleTools/Pickle.cs— payload buffer overrun (major)Resizeallocated_header.Length + newCapacitybut advertised_capacityAfterHeader = newCapacity, leaving the backing array_headerSize(4) bytes short on the first growth. A serialised asar header of 4089–4092 bytes overran the buffer (ArgumentException) during packing._headerSize + newCapacity, matching Chromium'sPickle::Resize.Changes
AsarSharp/Utils/Extensions.cs— newIsPathInsidehelper (normalising containment check).AsarSharp/AsarExtractor.cs— both traversal guards useIsPathInside.AsarSharp/PickleTools/Pickle.cs— correctedResizeallocation.All changes are minimal and localised; no public API or behaviour change beyond the fixes.
Testing
There is no automated test project for the C# solution and I don't have the WeMod runtime, so I verified by:
a/../../evilescape; the patched logic handles both while leaving every other size and all legitimate paths unchanged.Per
CONTRIBUTING.md, please build the solution in your environment to confirm compilation. Happy to adjust naming/placement (e.g. theIsPathInsidehelper) to fit project conventions.Fixes #142