vim-patch:9.2.0299: runtime(zip): may write using absolute paths (#38810)

Problem:  runtime(zip): may write using absolute paths
          (syndicate)
Solution: Detect this case and abort on Unix, warn in the documentation
          about possible issues

46f530e517

Co-authored-by: Christian Brabandt <cb@256bit.org>
(cherry picked from commit 4aa8969d29)

runtime/autoload/zip.vim

@@ -21,6 +21,7 @@
 " 2026 Feb 08 by Vim Project: use system() instead of :!
 " 2026 Mar 08 by Vim Project: Make ZipUpdatePS() check for powershell
 " 2026 Apr 01 by Vim Project: Detect more path traversal attacks
+" 2026 Apr 05 by Vim Project: Detect more path traversal attacks
 " License:	Vim License  (see vim's :help license)
 " Copyright:	Copyright (C) 2005-2019 Charles E. Campbell {{{1
 "		Permission is hereby granted to use and distribute this code,
@@ -395,9 +396,16 @@ fun! zip#Write(fname)
   if has("unix")
     let zipfile = substitute(a:fname,'zipfile://\(.\{-}\)::[^\\].*$','\1','')
     let fname   = substitute(a:fname,'zipfile://.\{-}::\([^\\].*\)$','\1','')
+    " fname should not start with a leading slash to avoid writing anywhere into the system
+    if fname =~ '^/'
+      call s:Mess('Error', "***error*** (zip#Write) Path Traversal Attack detected, not writing!")
+      call s:ChgDir(curdir,s:WARNING,"(zip#Write) unable to return to ".curdir."!")
+      return
+    endif
   else
     let zipfile = substitute(a:fname,'^.\{-}zipfile://\(.\{-}\)::[^\\].*$','\1','')
     let fname   = substitute(a:fname,'^.\{-}zipfile://.\{-}::\([^\\].*\)$','\1','')
+    " TODO: what to check on MS-Windows to avoid writing absolute paths?
   endif
   if fname =~ '^[.]\{1,2}/'
     let gnu_cmd = g:zip_zipcmd . ' -d ' . s:Escape(fnamemodify(zipfile,":p"),0) . ' ' . s:Escape(fname,0)

runtime/doc/pi_zip.txt

@@ -33,6 +33,10 @@ Copyright: Copyright (C) 2005-2015 Charles E Campbell	 *zip-copyright*
    also write to the file.  Currently, one may not make a new file in
    zip archives via the plugin.
 
+   The zip plugin tries to detect some common path traversal attack
+   patterns, but it may not catch all possible cases.  Please be very
+   careful when using this plugin with untrusted input.
+
    COMMANDS~
 								*zip-x*
    x : extract a listed file when the cursor is atop it

test/old/testdir/test_plugin_zip.vim

@@ -297,3 +297,22 @@ func Test_zip_fname_evil_path2()
   call assert_match('zipfile://.*::.*tmp/foobar', @%)
   bw!
 endfunc
+
+func Test_zip_fname_evil_path3()
+  CheckNotMSWindows
+  " needed for writing the zip file
+  CheckExecutable zip
+
+  call s:CopyZipFile("evil.zip")
+  defer delete("X.zip")
+  e X.zip
+
+  :1
+  let fname = 'payload.txt'
+  call search('\V' .. fname)
+  exe "normal \<cr>"
+  :w!
+  let mess  = execute(':mess')
+  call assert_match('Path Traversal Attack', mess)
+  bw!
+endfunc