libwmf integer/heap overflow

2006-07-10 / 2006-07-11
Risk: High
Local: Yes
Remote: Yes
CWE: N/A


CVSS Base Score: 7.5/10
Impact Subscore: 6.4/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

Sorry I don't have time to chase down multiple email addresses of alleged developers; so here this is after weeks of no response. POC is not attached unlike advisory says. It's not very difficult to exploit. ++++++++++++++++++++++++++++++++++++++++++++ Subject: libwmf integer/heap overflow ++++++++++++++++++++++++++++++++++++++++++++ Product: libwmf is a library for reading vector images in Micros&#248;ft's native Wind&#248;ws Metafile Format (WMF) and for either (a) displaying them in, e.g., an X window; or (b) converting them to more standard/open file formats such as, e.g., the W3C's XML-based Scaleable Vector Graphic (SVG) format. http://wvware.sourceforge.net/libwmf.html ++++++++++++++++++++++++++++++++++++++++++++ Vulnerable: I tested the most recent release, 0.2.8.4 ++++++++++++++++++++++++++++++++++++++++++++ Summary: An integer overflow in memory allocation leads to a heap overflow. ++++++++++++++++++++++++++++++++++++++++++++ Details: ------------------------------------------------------------------------ ------- file: src/meta.c +117 ------------------------------------------------------------------------ ------- wmf_error_t wmf_header_read (wmfAPI* API) { U16 u16a; U16 u16b; ...snip... if (API->File->wmfheader->HeaderSize == 9) { API->File->wmfheader->Version = wmf_read_16 (API); API->File->wmfheader->FileSize = wmf_read_32 (API,0,0); API->File->wmfheader->NumOfObjects = wmf_read_16 (API); 1] API->File->wmfheader->MaxRecordSize = wmf_read_32 (API,0,0); API->File->wmfheader->NumOfParams = wmf_read_16 (API); 1) This value is taken directly from the wmf file, later it will be used to allocate memory. It is not sanitized at any point. ------------------------------------------------------------------------ ------- ------------------------------------------------------------------------ ------- ------------------------------------------------------------------------ ------- file: src/player.c +86 ------------------------------------------------------------------------ ------- wmf_error_t wmf_scan (wmfAPI* API,unsigned long flags,wmfD_Rect* d_r) { wmfPlayer_t* P = (wmfPlayer_t*) API->player_data; ...snip... wmf_header_read (API); ...snip... 1] /* P->Parameters = (unsigned char*) wmf_malloc (API,(MAX_REC_SIZE (API)-3) * 2 * sizeof (unsigned char)); */ P->Parameters = (unsigned char*) wmf_malloc (API,(MAX_REC_SIZE(API) ) * 2 * sizeof (unsigned char)); /* HOLE */ WmfPlayMetaFile (API); 1) Overflow the calculation. ************************** static wmf_error_t WmfPlayMetaFile (wmfAPI* API) { int i; int byte; int changed; unsigned char* Par; ...snip... 1] Par = P->Parameters; ...snip... number = 0; do { if (++number < API->store.count) { atts = API->store.attrlist + number; } else { atts = &attrlist; wmf_attr_clear (API, atts); } 2] Size = wmf_read_32 (API,0,0); Function = wmf_read_16 (API); if ((Size == 3) && (Function == 0)) { if (SCAN (API)) wmf_write (API, Size, Function, "empty", atts->atts, 0, 0); break; /* Probably final record ?? */ } /* if ((Size > MAX_REC_SIZE (API)) || (Size < 3)) */ if (((Size - 3) > MAX_REC_SIZE (API)) || (Size < 3)) { WMF_ERROR (API,"libwmf: wmf with bizarre record size; bailing..."); WMF_ERROR (API," please send it to us at http://www.wvware.com/"); wmf_printf (API,"maximum record size = %un", (unsigned) MAX_REC_SIZE (API)); wmf_printf (API,"record size = %un",(unsigned) Size); API->err = wmf_E_BadFormat; break; } pos_params = WMF_TELL (API); if (pos_params < 0) { WMF_ERROR (API,"API's tell() failed on input stream!"); API->err = wmf_E_BadFile; break; } 3] for (i = 0; i < ((Size - 3) * 2); i++) { byte = WMF_READ (API); if (byte == (-1)) { WMF_ERROR (API,"Unexpected EOF!"); API->err = wmf_E_EOF; break; } Par[i] = (unsigned char) byte; /* VECTOR */ } 1) Points to the memory we allocated above. 2) Controls the number of bytes we write into the buffer. 3) Overflow the buffer by arbitrarily huge amounts. ------------------------------------------------------------------------ ------- ------------------------------------------------------------------------ ------- ++++++++++++++++++++++++++++++++++++++++++++ Mitigating factors: None. ++++++++++++++++++++++++++++++++++++++++++++ Workaround: Do not open up untrusted wmf files. ++++++++++++++++++++++++++++++++++++++++++++ Notes: libwmf is used by: wv abiword freetype gimp libgsf imagemagick ++++++++++++++++++++++++++++++++++++++++++++ Exploits: POC is provided that crashes in free(). The easiest way to test is to use the example conversion programs that come with libwmf, they are found in the src/convert/.libs directory: sean@hydra:~/libwmf-0.2.8.4/src/convert/.libs$ gcc -Wall exwmf.c sean@hydra:~/libwmf-0.2.8.4/src/convert/.libs$ ./a.out > evil.wmf sean@hydra:~/libwmf-0.2.8.4/src/convert/.libs$ gdb wmf2x GNU gdb 6.3-debian (gdb) r evil.wmf Starting program: /home/sean/libwmf-0.2.8.4/src/convert/.libs/wmf2x evil.wmf ERROR: player.c (482): Unexpected EOF! Program received signal SIGSEGV, Segmentation fault. 0x402d5354 in mallopt () from /lib/libc.so.6 (gdb) bt #0 0x402d5354 in mallopt () from /lib/libc.so.6 #1 0x402d415f in free () from /lib/libc.so.6 #2 0x402c283b in fclose () from /lib/libc.so.6 #3 0x4006e10e in wmf_file_close (API=0x804ad38) at bbuf.c:137 #4 0x4006d7d8 in wmf_lite_destroy (API=0x804ad38) at api.c:336 #5 0x40021e6f in wmf_api_destroy (API=0x804ad38) at wmf.c:167 #6 0x08048aec in wmf2x_draw (pdata=0xbffff8a0) at wmf2x.c:279 #7 0x08049518 in main (argc=1229353872, argv=0x49467390) at wmf2x.c:401 (gdb) up 1 #1 0x402d415f in free () from /lib/libc.so.6 (gdb) x/4x $ebp 0xbffff654: 0xbffff688 0x402c283b 0x08053258 0x00000000 ^^^ chunk being free()'d (gdb) x/30x 0x08053258-16 0x8053248: 0x41414141 0x41414141 0x41414141 0x41414141 ^^^^^ chunk header 0x8053258: 0x00000000 0x40087000 0x40087000 0x40087000 0x8053268: 0x40087000 0x40087000 0x40087000 0x40087000 0x8053278: 0x40088000 0x00000000 0x00000000 0x00000000 0x8053288: 0x00000000 0x4038c440 0x00000006 0x00000000 0x8053298: 0x0804bb70 0x08000000 0x080532f0 0x00001018 0x80532a8: 0x00000000 0x0804bbe8 0x08053308 0xffffffff 0x80532b8: 0x0804bc30 0x0804bc40 (gdb) ++++++++++++++++++++++++++++++++++++++++++++ -- [ sean ] [ pgp key id: 0x421C8CD9 ] [ The advantage of a bad memory is that one enjoys several ] [ times the same good things for the first time. ]


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