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Problem: read_compound() in spellfile.c computes the size of the regex
pattern buffer using signed-int arithmetic on the attacker
controlled SN_COMPOUND sectionlen. With sectionlen=0x40000008
and UTF-8 encoding active the multiplication wraps to 27 while
the per-byte loop writes up to ~1B bytes, overflowing the heap.
Reachable when loading a crafted .spl file (e.g. via 'set spell'
after a modeline sets 'spelllang'). The cp/ap/crp allocations
have the same int + 1 overflow class (Daniel Cervera)
Solution: Use type size_t as buffer size and reject values larger than
COMPOUND_MAX_LEN (100000). Apply the same size_t treatment to
the cp/ap/crp allocations.
Github Advisory:
https://github.com/vim/vim/security/advisories/GHSA-q4jv-r9gj-6cwv
9299332917
Co-authored-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>