ytnef: heap-based buffer overflow in SwapDWord (ytnef.c)

Description:
ytnef is Yeraze’s TNEF Stream Reader – for winmail.dat files.

The complete ASan output of the issue:

# ytnefprint $FILE
==12532==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000000014 at pc 0x7f8e3c35544e bp 0x7ffeb883d890 sp 0x7ffeb883d888                                                                         
READ of size 1 at 0x602000000014 thread T0                                                                                                                                                                        
    #0 0x7f8e3c35544d in SwapDWord /tmp/ytnef-1.9.2/lib/ytnef.c:180:28                                                                                                                                            
    #1 0x7f8e3c35544d in TNEFFillMapi /tmp/ytnef-1.9.2/lib/ytnef.c:430                                                                                                                                            
    #2 0x7f8e3c360b47 in TNEFParse /tmp/ytnef-1.9.2/lib/ytnef.c:1184:15                                                                                                                                           
    #3 0x7f8e3c35f9d3 in TNEFParseFile /tmp/ytnef-1.9.2/lib/ytnef.c:1042:10                                                                                                                                       
    #4 0x508814 in main /tmp/ytnef-1.9.2/ytnefprint/main.c:80:9                                                                                                                                                   
    #5 0x7f8e3b47578f in __libc_start_main /tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/csu/../csu/libc-start.c:289                                                                                        
    #6 0x419c38 in _start (/usr/bin/ytnefprint+0x419c38)                                                                                                                                                          
                                                                                                                                                                                                                  
0x602000000014 is located 0 bytes to the right of 4-byte region [0x602000000010,0x602000000014)                                                                                                                   
allocated by thread T0 here:                                                                                                                                                                                      
    #0 0x4cf7e0 in calloc /tmp/portage/sys-libs/compiler-rt-sanitizers-4.0.0/work/compiler-rt-4.0.0.src/lib/asan/asan_malloc_linux.cc:74                                                                          
    #1 0x7f8e3c36072a in TNEFParse /tmp/ytnef-1.9.2/lib/ytnef.c:1154:12                                                                                                                                           
    #2 0x7f8e3c35f9d3 in TNEFParseFile /tmp/ytnef-1.9.2/lib/ytnef.c:1042:10                                                                                                                                       
    #3 0x508814 in main /tmp/ytnef-1.9.2/ytnefprint/main.c:80:9                                                                                                                                                   
    #4 0x7f8e3b47578f in __libc_start_main /tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/csu/../csu/libc-start.c:289                                                                                        
                                                                                                                                                                                                                  
SUMMARY: AddressSanitizer: heap-buffer-overflow /tmp/ytnef-1.9.2/lib/ytnef.c:180:28 in SwapDWord                                                                                                                  
Shadow bytes around the buggy address:                                                                                                                                                                            
  0x0c047fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00                                                                                                                                                 
  0x0c047fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00                                                                                                                                                 
  0x0c047fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00                                                                                                                                                 
  0x0c047fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00                                                                                                                                                 
  0x0c047fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00                                                                                                                                                 
=>0x0c047fff8000: fa fa[04]fa fa fa fa fa fa fa fa fa fa fa fa fa                                                                                                                                                 
  0x0c047fff8010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa                                                                                                                                                 
  0x0c047fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa                                                                                                                                                 
  0x0c047fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa                                                                                                                                                 
  0x0c047fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa                                                                                                                                                 
  0x0c047fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa                                                                                                                                                 
Shadow byte legend (one shadow byte represents 8 application bytes):                                                                                                                                              
  Addressable:           00                                                                                                                                                                                       
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==12532==ABORTING

Affected version:
1.9.2

Fixed version:
N/A

Commit fix:
N/A

Credit:
This bug was discovered by Agostino Sarubbo of Gentoo.

CVE:
CVE-2017-9472

Reproducer:
https://github.com/asarubbo/poc/blob/master/00245-ytnef-heapoverflow-SwapDWord

Timeline:
2017-03-27: bug discovered and reported to upstream
2017-05-24: blog post about the issue
2017-06-07: CVE assigned

Note:
This bug was found with American Fuzzy Lop.

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ytnef: heap-based buffer overflow in SwapDWord (ytnef.c)

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