Bound mcpb unpack against decompression bombs and malformed central directories#273
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aosmcleod wants to merge 1 commit into
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Bound mcpb unpack against decompression bombs and malformed central directories#273aosmcleod wants to merge 1 commit into
aosmcleod wants to merge 1 commit into
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…ories unpackExtension inflated the whole archive with unzipSync and no size limit, and trusted the central-directory entry count — a small, highly compressible .mcpb could exhaust memory. The central-directory parse also read at offsets derived from untrusted ZIP fields with no bounds checks. Add configurable maxUncompressedBytes (default 1 GiB) and maxEntries (default 100k) caps, enforced from the central directory before decompression. Make the central-directory pass run on all platforms with bounds-checked reads so a truncated/malformed directory can't throw a RangeError (Unix attribute extraction is still gated to Unix). Adds tests for normal unpack and for size/entry-limit rejection. Note: the size cap relies on the archive's declared uncompressed sizes; fully bounding a deliberately under-declaring archive needs streaming decompression with a running byte cap, which would be a larger change (follow-up). Fixes modelcontextprotocol#266 (central-directory bounds is item 4 of modelcontextprotocol#267)
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Problem
unpackExtensiondecompresses the whole archive withunzipSyncand no size limit, and trusts the central-directory entry count without bound — a small, highly compressible.mcpb(zip bomb) can exhaust memory and crash the process (#266). Separately, the central-directory pass reads at offsets derived from untrusted ZIP fields with no bounds validation, so a malformed/truncated directory throws aRangeError(item 4 of #267).Fix
maxUncompressedBytes(default 1 GiB) andmaxEntries(default 100k), enforced from the central directory before decompression.Limitation (called out honestly)
The size cap relies on the archive's declared uncompressed sizes. Fully bounding an archive that deliberately under-declares its sizes requires streaming decompression with a running byte cap (fflate
Unzip+ondata), which is a larger rewrite — flagged as a follow-up rather than done here.Test
Adds
test/unpack-limits.test.ts: a normal archive unpacks within defaults; archives exceedingmaxUncompressedBytesormaxEntriesare rejected without extracting.yarn lint+yarn test(this suite) green.Fixes #266.