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fix(nbt): cap skim recursion depth to reject hostile region files - #1
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A region file can nest NBT tags deeply enough to overflow the stack while the map skims block-state names, which aborts the whole process. The region decoder runs on untrusted input from map ingest, so the crash is remotely reachable. Bound the skim to a fixed recursion depth and treat anything deeper as corrupt.
dekrom
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Aug 28, 2026
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Verified the crash reproduces on main (deeply-nested NBT in an ingested region overflows the stack and aborts the process) and that this cap rejects it cleanly. The skim is the only recursive path in the codec and both entry points are bounded. Thanks for catching this.
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A crafted region can nest NBT tags deeply enough to overflow the stack while the map skims block-state names, which aborts the process. The decoder runs on untrusted ingest input, so the crash is remotely reachable. The skim is now bounded to a fixed recursion depth and anything deeper is treated as corrupt.