commit 7679fd1: [Minor] Magic: try avoid false positive exe detection

[Andrew Lewis]

Author: Andrew Lewis
Date: 2021-01-04 13:41:04 +0200
URL: https://github.com/rspamd/rspamd/commit/7679fd1222d6e7b6bbead83aa0ea7c2a5effdc21 (refs/pull/3595/head)

[Minor] Magic: try avoid false positive exe detection

---
 lualib/lua_magic/heuristics.lua | 18 ++++++++++++++++++
 lualib/lua_magic/patterns.lua   |  3 ++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/lualib/lua_magic/heuristics.lua b/lualib/lua_magic/heuristics.lua
index d9a7702a4..fb0a4b7c2 100644
--- a/lualib/lua_magic/heuristics.lua
+++ b/lualib/lua_magic/heuristics.lua
@@ -471,4 +471,22 @@ exports.pdf_format_heuristic = function(input, log_obj, pos, part)
   return 'pdf',weight
 end
 
+exports.pe_part_heuristic = function(input, log_obj, pos, part)
+  if not input then
+    return
+  end
+
+  local pe_ptr_bin = input:sub(60, 64)
+  if #pe_ptr_bin ~= 4 then
+    return
+  end
+
+  local pe_ptr = rspamd_util.unpack("<H", pe_ptr_bin)
+  if pe_ptr ~= pos then
+    return
+  end
+
+  return 'exe',15
+end
+
 return exports
diff --git a/lualib/lua_magic/patterns.lua b/lualib/lua_magic/patterns.lua
index 5e62b47f9..8bdc7ea44 100644
--- a/lualib/lua_magic/patterns.lua
+++ b/lualib/lua_magic/patterns.lua
@@ -105,6 +105,7 @@ local patterns = {
         string = [[PE\x{00}\x{00}]],
         position = {'>=', 0x3c + 4},
         weight = 15,
+        heuristic = heuristics.pe_part_heuristic,
       }
     }
   },
@@ -458,4 +459,4 @@ local patterns = {
   },
 }
 
-return patterns
\ No newline at end of file
+return patterns