new file mode 100644
@@ -0,0 +1,110 @@
+From 48287480f53acfb5e6f9172e571ed2f0508dfab2 Mon Sep 17 00:00:00 2001
+From: Hirohito Higashi <h.east.727@gmail.com>
+Date: Mon, 22 Jun 2026 13:00:36 +0900
+Subject: [PATCH 16/17] patch 9.2.0725: [security]: Stack out-of-bounds write
+ in spell_soundfold_sal()
+
+Problem: [security]: A crafted spell file with non-collapsing SAL rules
+ can make soundfold() write one byte past the end of the
+ MAXWLEN result buffer. This is the same class of
+ out-of-bounds write as GHSA-q8mh-6qm3-25g4 (fixed in 9.2.0698
+ for the SOFO branch), found while auditing the surrounding
+ code.
+Solution: Bound the single-byte SAL result writes and the terminating
+ NUL to MAXWLEN - 1, matching the SOFO branch.
+
+The single-byte branch of spell_soundfold_sal() guarded its writes with
+"reslen < MAXWLEN", allowing reslen to reach MAXWLEN (254). The trailing
+"res[reslen] = NUL" then wrote at index 254 of the 254-byte stack buffer
+res[MAXWLEN], an off-by-one out-of-bounds write. Input is case-folded to
+about 253 characters, so a 253-character argument together with a SAL map
+that does not collapse (collapse_result false) reaches the boundary.
+
+Related to previous issue
+[GHSA-q8mh-6qm3-25g4](https://github.com/vim/vim/security/advisories/GHSA-q8mh-6qm3-25g4)
+(9.2.0698)
+
+Github Security Advisory:
+https://github.com/vim/vim/security/advisories/GHSA-m3hf-xcm3-xhm2
+
+Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
+Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
+Signed-off-by: Christian Brabandt <cb@256bit.org>
+
+Upstream-Status: Backport [https://github.com/vim/vim/commit/d22ff1c955ff87e8273210eae125aab0e85b6c30]
+CVE: CVE-2026-59857
+Signed-off-by: Siddharth Doshi <sdoshi@mvista.com>
+---
+ src/spell.c | 6 +++---
+ src/testdir/test_spellfile.vim | 24 ++++++++++++++++++++++++
+ 2 files changed, 27 insertions(+), 3 deletions(-)
+
+diff --git a/src/spell.c b/src/spell.c
+index a7909ef46e..05d6f0159d 100644
+--- a/src/spell.c
++++ b/src/spell.c
+@@ -3516,7 +3516,7 @@ spell_soundfold_sal(slang_T *slang, char_u *inword, char_u *res)
+ // no '<' rule used
+ i += k - 1;
+ z = 0;
+- while (*s != NUL && s[1] != NUL && reslen < MAXWLEN)
++ while (*s != NUL && s[1] != NUL && reslen < MAXWLEN - 1)
+ {
+ if (reslen == 0 || res[reslen - 1] != *s)
+ res[reslen++] = *s;
+@@ -3526,7 +3526,7 @@ spell_soundfold_sal(slang_T *slang, char_u *inword, char_u *res)
+ c = *s;
+ if (strstr((char *)pf, "^^") != NULL)
+ {
+- if (c != NUL)
++ if (c != NUL && reslen < MAXWLEN - 1)
+ res[reslen++] = c;
+ STRMOVE(word, word + i + 1);
+ i = 0;
+@@ -3545,7 +3545,7 @@ spell_soundfold_sal(slang_T *slang, char_u *inword, char_u *res)
+
+ if (z0 == 0)
+ {
+- if (k && !p0 && reslen < MAXWLEN && c != NUL
++ if (k && !p0 && reslen < MAXWLEN - 1 && c != NUL
+ && (!slang->sl_collapse || reslen == 0
+ || res[reslen - 1] != c))
+ // condense only double letters
+diff --git a/src/testdir/test_spellfile.vim b/src/testdir/test_spellfile.vim
+index d04d024911..c8c7ac2642 100644
+--- a/src/testdir/test_spellfile.vim
++++ b/src/testdir/test_spellfile.vim
+@@ -383,6 +383,30 @@ func Test_spellfile_format_error()
+ let &rtp = save_rtp
+ endfunc
+
++" An over-length soundfold() argument must not overflow the MAXWLEN result
++" buffer in the single-byte branch of spell_soundfold_sal().
++func Test_spellfile_soundfold_sal_overflow()
++ let save_enc = &encoding
++ set encoding=latin1
++ " A SAL map that appends without collapsing, so the result is not shorter
++ " than the input.
++ call writefile(['SET ISO8859-1', 'SAL collapse_result false',
++ \ 'SAL a aaaa', 'SAL b bbbb'], 'Xsal.aff')
++ call writefile(['2', 'hello', 'world'], 'Xsal.dic')
++ mkspell! Xsal Xsal
++ set spl=Xsal.latin1.spl spell
++
++ " 253 input characters hit the buffer boundary; the result must not exceed
++ " MAXWLEN - 1.
++ call assert_true(strlen(soundfold(repeat('a', 253))) <= 253)
++
++ set nospell spl& spelllang&
++ call delete('Xsal.aff')
++ call delete('Xsal.dic')
++ call delete('Xsal.latin1.spl')
++ let &encoding = save_enc
++endfunc
++
+ " Test for format errors in suggest file
+ func Test_sugfile_format_error()
+ let save_rtp = &rtp
+--
+2.44.4
+
@@ -44,6 +44,7 @@ SRC_URI = "git://github.com/vim/vim.git;branch=master;protocol=https \
file://CVE-2026-57452.patch \
file://CVE-2026-57455.patch \
file://CVE-2026-59856.patch \
+ file://CVE-2026-59857.patch \
"
PV .= ".1683"