Medium [CVE-2026-57455] Denial of Service via stack out-of-bounds write in spell_soundfold_sofo

Vim is an open source, command line text editor. Prior to 9.2.0698, the single-byte branch of spell_soundfold_sofo() in src/spell.c translates a word through a spell file's SOFO (sound-folding) byte map into a caller-owned result buffer.

Its copy loop advances the output index ri with no upper bound and terminates only on the input NUL, writing one byte per input byte into the MAXWLEN-element stack buffer the caller provides.

A word longer than MAXWLEN, passed to soundfold() (or reached via sound-based spell suggestion) while a SOFO-based spell language is active, therefore writes past the end of that buffer. This is a stack out-of-bounds write that corrupts the call frame and crashes the editor.

This vulnerability is fixed in 9.2.0698. A memory corruption flaw in Vim allows an attacker to cause a Denial of Service (DoS).

When a SOFO-based spell language is active, providing an excessively long word to the spell checker triggers a stack out-of-bounds write in the spell_soundfold_sofo() function, causing the editor to crash.

Exploitation requires a user to open a specially crafted file or encounter a long word via spell suggestion while a SOFO-based spell language is active, leading to a Denial of Service. This is not a default configuration in most Red Hat environments, limiting the attack surface.