We discover a buffer over-write problem in the T::NEFFillMapi functiion.
The root cause of this problem is zero-byte allocation problem.
in lib/ytnef.c:485
mp->data = "" sizeof(variableLength));
the value of mp->count can be zero and the write and read operation cause problems in
TNEFFillMapi (ytnef.c:508) ,TNEFFillMapi (ytnef.c:517), TNEFFillMapi (ytnef.c:526).
The following patch can solve this issue:
--- ../ytnef/lib/ytnef.c 2017-05-14 19:44:47.417979746 +0800
+++ lib/ytnef.c 2017-05-16 08:59:28.088356920 +0800
@@ -479,7 +482,9 @@
d += 4;
count = 0;
}
- mp->data = "" sizeof(variableLength));
+ if (mp->count>0){
+ mp->data = "" sizeof(variableLength));
+ }else{ mp->data="" }
ALLOCCHECK(mp->data);
vl = mp->data;
} else {
To verify this, use the testcase from:
https://github.com/bingosxs/fuzzdata/raw/master/ytnef-1.9/TNEFFillMapi-over-write.tnef
run the sample with command:
ytnef/.libs/ytnef -vTNEFFillMapi-over-write.tnef
The tracelog is:
=================================================================valgrind ./bin/ytnef -v ../../libytnef0/testenv/out/crashes/id\:000015\,sig\:06\,src\:000007\,op\:int16\,pos\:2540\,val\:+1 ==12741== Memcheck, a memory error detector ==12741== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al. ==12741== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info ==12741== Command: ./bin/ytnef -v ../../libytnef0/testenv/out/crashes/id:000015,sig:06,src:000007,op:int16,pos:2540,val:+1 ==12741== Attempting to parse ../../libytnef0/testenv/out/crashes/id:000015,sig:06,src:000007,op:int16,pos:2540,val:+1... ==12741== Invalid write of size 4 ==12741== at 0x4E3F89A: TNEFFillMapi (ytnef.c:504) ==12741== by 0x4E3D582: TNEFMapiProperties (ytnef.c:396) ==12741== by 0x4E46C49: TNEFParse (ytnef.c:1184) ==12741== by 0x4E45C85: TNEFParseFile (ytnef.c:1042) ==12741== by 0x4017F8: main (main.c:125) ==12741== Address 0x542a488 is 8 bytes after a block of size 0 alloc'd ==12741== at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==12741== by 0x4E3F213: TNEFFillMapi (ytnef.c:482) ==12741== by 0x4E3D582: TNEFMapiProperties (ytnef.c:396) ==12741== by 0x4E46C49: TNEFParse (ytnef.c:1184) ==12741== by 0x4E45C85: TNEFParseFile (ytnef.c:1042) ==12741== by 0x4017F8: main (main.c:125) ==12741== ==12741== Invalid write of size 8 ==12741== at 0x4E3FA0A: TNEFFillMapi (ytnef.c:513) ==12741== by 0x4E3D582: TNEFMapiProperties (ytnef.c:396) ==12741== by 0x4E46C49: TNEFParse (ytnef.c:1184) ==12741== by 0x4E45C85: TNEFParseFile (ytnef.c:1042) ==12741== by 0x4017F8: main (main.c:125) ==12741== Address 0x542a480 is 0 bytes after a block of size 0 alloc'd ==12741== at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==12741== by 0x4E3F213: TNEFFillMapi (ytnef.c:482) ==12741== by 0x4E3D582: TNEFMapiProperties (ytnef.c:396) ==12741== by 0x4E46C49: TNEFParse (ytnef.c:1184) ==12741== by 0x4E45C85: TNEFParseFile (ytnef.c:1042) ==12741== by 0x4017F8: main (main.c:125) ==12741== ==12741== Invalid read of size 4 ==12741== at 0x4E3FA50: TNEFFillMapi (ytnef.c:515) ==12741== by 0x4E3D582: TNEFMapiProperties (ytnef.c:396) ==12741== by 0x4E46C49: TNEFParse (ytnef.c:1184) ==12741== by 0x4E45C85: TNEFParseFile (ytnef.c:1042) ==12741== by 0x4017F8: main (main.c:125) ==12741== Address 0x542a488 is 8 bytes after a block of size 0 alloc'd ==12741== at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==12741== by 0x4E3F213: TNEFFillMapi (ytnef.c:482) ==12741== by 0x4E3D582: TNEFMapiProperties (ytnef.c:396) ==12741== by 0x4E46C49: TNEFParse (ytnef.c:1184) ==12741== by 0x4E45C85: TNEFParseFile (ytnef.c:1042) ==12741== by 0x4017F8: main (main.c:125) ==12741== ==12741== Invalid read of size 4 ==12741== at 0x4E3FAA1: TNEFFillMapi (ytnef.c:522) ==12741== by 0x4E3D582: TNEFMapiProperties (ytnef.c:396) ==12741== by 0x4E46C49: TNEFParse (ytnef.c:1184) ==12741== by 0x4E45C85: TNEFParseFile (ytnef.c:1042) ==12741== by 0x4017F8: main (main.c:125) ==12741== Address 0x542a488 is 8 bytes after a block of size 0 alloc'd ==12741== at 0x4C2FB55: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==12741== by 0x4E3F213: TNEFFillMapi (ytnef.c:482) ==12741== by 0x4E3D582: TNEFMapiProperties (ytnef.c:396) ==12741== by 0x4E46C49: TNEFParse (ytnef.c:1184) ==12741== by 0x4E45C85: TNEFParseFile (ytnef.c:1042) ==12741== by 0x4017F8: main (main.c:125) ==12741== Corrupted file detected at ytnef.c : 509 ERROR Parsing MAPI block ==12741== ==12741== HEAP SUMMARY: ==12741== in use at exit: 9 bytes in 1 blocks ==12741== total heap usage: 167 allocs, 166 frees, 18,316 bytes allocated ==12741== ==12741== LEAK SUMMARY: ==12741== definitely lost: 9 bytes in 1 blocks ==12741== indirectly lost: 0 bytes in 0 blocks ==12741== possibly lost: 0 bytes in 0 blocks ==12741== still reachable: 0 bytes in 0 blocks ==12741== suppressed: 0 bytes in 0 blocks ==12741== Rerun with --leak-check=full to see details of leaked memory ==12741== ==12741== For counts of detected and suppressed errors, rerun with: -v ==12741== ERROR SUMMARY: 5 errors from 4 contexts (suppressed: 0 from 0)Credits: National Computer Network Emergency Response Technical Team/Coordination Center of China. Wang Bo, Fan Lejun, Wu Qian. TCA, ISCAS.