LG MRA58K – Missing Bounds-Checking in AVI Stream Parsing

• Exploit Database
• 117 阅读

• 作者： Google Security Research
  日期： 2017-06-13
• 类别：

  • dos
  平台：

  • android
• 来源：https://www.exploit-db.com/exploits/42170/
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  Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1206   Missing bounds-checking in AVI stream parsing   When parsing AVI files, CAVIFileParser uses the stream count from the AVI header to allocate backing storage for storing metadata about the streams (member variable m_aStream). However, the number of stream headers we parse is never validated against this allocation size during parsing, so we can write further metadata past the end of this buffer by constructing a file which contains more stream headers than expected.   The allocation happens here:   int CAVIFileParser::ParseChunkAviHdr(int a2, unsigned int chunk_size) { struct AviHeader *avih; int result;   // snip some sanity checking (have we already found an &apos;avih&apos; chunk, is this // chunk large enough to contain an avi header.)   result = AVISourceReader::AVI_fread(this->source, avih, sizeof(struct AviHeader), 1); if ( result <= 0 ) { // snip... } else { stream_count = avih->dwStreams; // <-- this is an attacker-controlled count this->m_aStreamCount = stream_count; this->m_aStream = malloc(stream_count * sizeof(struct AviStream)); this->m_aStreamIndex = -1;   // snip... }   return 1; }   There doesn&apos;t appear to be any integer overflow checking in the multiplication either; so if the current issue is directly fixed there could still be a vulnerability if stream_count * sizeof(struct AviStream) overflows.   this->m_aStreamIndex is incremented without checking in CAVIFileParser::ParseChild and used as an index into m_aStream in several places without checking, including in CAVIFileParser::ParseChunkStrHdr and CAVIFileParser::ParseChunkStrFmt.   Several of the values that we can get written out of bounds are pointers to controlled data, which is an interesting exploitation primitive. I&apos;ve attached a PoC file and script to generate it which results in overlapping a SRIFFNode* with the contents of a &apos;strf&apos; chunk, resulting in a free of an attacker controlled pointer - in this case, 0x41414141. Since the structure sizes are dependent on the version of the library, this may not work on different builds, but it will hopefully cause a crash regardless.   Build fingerprint: &apos;lge/p1_global_com/p1:6.0/MRA58K/1624210305d45:user/release-keys&apos; Revision: &apos;11&apos; ABI: &apos;arm&apos; pid: 19481, tid: 19585, name: Binder_2>>> /system/bin/mediaserver <<< signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x4140007c r0 00000002r1 00000012r2 ffffffd0r3 f6b572f0 AM write failed: Broken pipe r4 f6b572e8r5 41414141r6 f5fb6000r7 41400000 r8 f155c748r9 f6b4a594sl 00000001fp f000081c ip 41400048sp f00005f8lr f6b2c7a7pc f6b29826cpsr 200f0030   backtrace: #00 pc 00055826/system/lib/libc.so (ifree+49) #01 pc 000587a3/system/lib/libc.so (je_free+374) #02 pc 000058f3/system/lib/liblg_parser_avi.so (_ZN14CAVIFileParser15DeleteSRIFFNodeEP9SRIFFNode+54) #03 pc 00005915/system/lib/liblg_parser_avi.so (_ZN14CAVIFileParser7DestroyEv+12) #04 pc 00005a33/system/lib/liblg_parser_avi.so (_ZN14CAVIFileParserD1Ev+14) #05 pc 00005a45/system/lib/liblg_parser_avi.so (_ZN14CAVIFileParserD0Ev+4) #06 pc 0000442f/system/lib/liblg_parser_avi.so (_ZN9AVIParser5CloseEv+12) #07 pc 00025baf/system/lib/libLGParserOSAL.so (_ZN7android14LGAVIExtractorD1Ev+26)     Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/42170.zip