Exploit-DB #39494
Description: libxml2 - htmlCurrentChar Heap Buffer Overread
Type: dos
Platform: linux
Date: 2016-02-24
Author: Google Security Research

Exploit:
Source: https://code.google.com/p/google-security-research/issues/detail?id=636

The following crash due to a heap-based out-of-bounds memory read can be observed in an ASAN build of latest stable libxml2 (2.9.3, released 4 days ago), by feeding a malformed file to xmllint ("$ ./xmllint --html /path/to/file"):

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==26202==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x62100001c900 at pc 0x[PII_REDACTED]f9 bp 0x7ffd791c7f90 sp 0x7ffd791c7f88
READ of size 1 at 0x62100001c900 thread T0
    #0 0x8073f8 in htmlCurrentChar libxml2-2.9.3/HTMLparser.c:439:6
    #1 0x80ee62 in htmlParseCharDataInternal libxml2-2.9.3/HTMLparser.c:3011:8
    #2 0x821b85 in htmlParseCharData libxml2-2.9.3/HTMLparser.c:3061:5
    #3 0x7df875 in htmlParseContentInternal libxml2-2.9.3/HTMLparser.c:4634:3
    #4 0x7e2f0f in htmlParseDocument libxml2-2.9.3/HTMLparser.c:4769:5
    #5 0x802c55 in htmlDoRead libxml2-2.9.3/HTMLparser.c:6741:5
    #6 0x8030b6 in htmlReadFile libxml2-2.9.3/HTMLparser.c:6799:13
    #7 0x4f47a5 in parseAndPrintFile libxml2-2.9.3/xmllint.c:2248:8
    #8 0x4ebe8f in main libxml2-2.9.3/xmllint.c:3759:7

0x62100001c900 is located 0 bytes to the right of 4096-byte region [0x62100001b900,0x62100001c900)
allocated by thread T0 here:
    #0 0x4b8b68 in malloc llvm/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:40
    #1 0xa01a0c in xmlBufCreate libxml2-2.9.3/buf.c:137:32
    #2 0x550aca in xmlSwitchInputEncodingInt libxml2-2.9.3/parserInternals.c:1205:34
    #3 0x54f5ce in xmlSwitchToEncodingInt libxml2-2.9.3/parserInternals.c:1281:12
    #4 0x54f278 in xmlSwitchEncoding libxml2-2.9.3/parserInternals.c:1101:11
    #5 0x808eea in htmlCurrentChar libxml2-2.9.3/HTMLparser.c:518:13
    #6 0x804a38 in htmlParseNameComplex libxml2-2.9.3/HTMLparser.c:2496:9
    #7 0x7cc29d in htmlParseName libxml2-2.9.3/HTMLparser.c:2483:12
    #8 0x7ec211 in htmlParseDocTypeDecl libxml2-2.9.3/HTMLparser.c:3424:12
    #9 0x7debf4 in htmlParseContentInternal libxml2-2.9.3/HTMLparser.c:4585:3
    #10 0x7e2f0f in htmlParseDocument libxml2-2.9.3/HTMLparser.c:4769:5
    #11 0x802c55 in htmlDoRead libxml2-2.9.3/HTMLparser.c:6741:5
    #12 0x8030b6 in htmlReadFile libxml2-2.9.3/HTMLparser.c:6799:13
    #13 0x4f47a5 in parseAndPrintFile libxml2-2.9.3/xmllint.c:2248:8
    #14 0x4ebe8f in main libxml2-2.9.3/xmllint.c:3759:7

SUMMARY: AddressSanitizer: heap-buffer-overflow libxml2-2.9.3/HTMLparser.c:439:6 in htmlCurrentChar
Shadow bytes around the buggy address:
  0x0c427fffb8d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c427fffb8e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c427fffb8f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c427fffb900: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c427fffb910: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c427fffb920:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c427fffb930: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c427fffb940: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c427fffb950: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c427fffb960: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c427fffb970: 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
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  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
==26202==ABORTING
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The crash was reported at https://bugzilla.gnome.org/show_bug.cgi?id=758606. Attached is an XML file which triggers the crash.


Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39494.zip