From e85fc92a6ba4b2bf165b360846b6fb460e98ab52 Mon Sep 17 00:00:00 2001 From: zeertzjq Date: Sat, 28 Feb 2026 08:11:48 +0800 Subject: [PATCH] vim-patch:9.2.0075: [security]: Buffer underflow with emacs tag file Problem: When parsing a malformed Emacs-style tags file, a 1-byte heap-buffer-underflow read occurs if the 0x7f delimiter appears at the very beginning of a line. This happens because the code attempts to scan backward for a tag name from the delimiter without checking if space exists. (ehdgks0627, un3xploitable) Solution: Add a check to ensure the delimiter (p_7f) is not at the start of the buffer (lbuf) before attempting to isolate the tag name. GitHub Advisory: https://github.com/vim/vim/security/advisories/GHSA-xcc8-r6c5-hvwv https://github.com/vim/vim/commit/9b7dfa2948c9e1e5e32a5812812d580c7879f4a0 Co-authored-by: Christian Brabandt --- test/old/testdir/test_taglist.vim | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/test/old/testdir/test_taglist.vim b/test/old/testdir/test_taglist.vim index d2e6036e7b..869d684987 100644 --- a/test/old/testdir/test_taglist.vim +++ b/test/old/testdir/test_taglist.vim @@ -333,4 +333,20 @@ func Test_evil_emacs_tagfile() set tags& endfunc +" This used to crash Vim due to a heap-buffer-underflow +func Test_emacs_tagfile_underflow() + CheckFeature emacs_tags + " The sequence from the crash artifact: + let lines = [ + \ "\x0c\xff\xffT\x19\x8a", + \ "\x19\x19\x0dtags\x19\x19\x19\x00\xff\xff\xff", + \ "\x7f3\x0c" + \ ] + call writefile(lines, 'Xtags', 'D') + set tags=Xtags + call assert_fails(':tag a', 'E431:') + + set tags& +endfunc + " vim: shiftwidth=2 sts=2 expandtab