[NEWS] Clam AntiVirus Multiple DoS (MS-Expand File Handling, Cabinet File Handling)

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  Clam AntiVirus Multiple DoS (MS-Expand File Handling, Cabinet File 
Handling)
------------------------------------------------------------------------


SUMMARY

 <http://www.clamav.net/> Clam AntiVirus is a GPL anti-virus toolkit for 
UNIX.

Lack of proper validation by the Clam AntiVirus allows attackers to cause 
Clam AntiVirus to enter to infinite loop or exhaust file descriptors pool 
and memory.

DETAILS

Vulnerable Systems:
 * ClamAV version 0.85 and prior

Immune Systems:
 * ClamAV version 0.86

MS-Expand File Handling:
The vulnerability specifically exists due to improper behavior during 
exceptional conditions.

Code Snips:
libclamav/scanners.c:
    static int cli_scanszdd(...)
    {
      [...]
      FILE *tmp = NULL, *in;

      cli_dbgmsg("in cli_scanmscomp()\n");

      if((in = fdopen(dup(desc), "rb")) == NULL) {
        cli_dbgmsg("SZDD: Can't open descriptor %d\n", desc);
        return CL_EMSCOMP;
      }

      if((tmp = tmpfile()) == NULL) {
        cli_dbgmsg("SZDD: Can't generate temporary file.\n");
        fclose(in);
        return CL_ETMPFILE;
      }

      if(cli_msexpand(in, tmp) == -1) {
        cli_dbgmsg("SZDD: msexpand failed.\n");
        return CL_EMSCOMP;
      }

      [...]
    }

Each time the cli_msexpand() function fails , two file descriptors ('in'  
and 'tmp') are leaked. As they are both opened using fopen(), there is  
also a memory leak (2 * 364 bytes). This allows an attacker to exhaust all 
of the available file descriptors fairly quickly with around 1,000  
malformed files.

Successful exploitation allows attackers to exhaust file descriptors  pool 
and memory. Anti-virus detection functionality will fail if there is no 
file descriptors available with which to open files. Remote exploitation 
can be achieved by sending a malicious file in an e-mail message or during 
an HTTP session.

Cabinet File Handling:
The vulnerability specifically exists due to insufficient validation on 
cabinet file header data. The ENSURE_BITS() macro fails to check for zero 
length reads, allowing a carefully constructed cabinet file to cause an 
infinite loop. The ENSURE_BITS() macro is executed indirectly through the 
READ_BITS macro and is called from the mszipd_compress function.

Code Snips:
libclamav/mspack/mszipd.c
#define ENSURE_BITS(nbits) do { \
  while (bits_left < (nbits)) {  \
    if (i_ptr >= i_end) {  \
      if (zipd_read_input(zip)) return zip->error; \
        i_ptr = zip->i_ptr;  \
        i_end = zip->i_end; \
   } \
   bit_buffer |= *i_ptr++ << bits_left; bits_left += 8;  \
  }  \
} while (0)

#define READ_BITS(val, nbits) do {  \
 ENSURE_BITS(nbits); (val) = PEEK_BITS(nbits); REMOVE_BITS(nbits); \
} while (0)

static int zipd_read_input(struct mszipd_stream *zip) {
 int read = zip->sys->read(zip->input,  &zip->inbuf[0], 
(int)zip->inbuf_size);
  if (read < 0) return zip->error = MSPACK_ERR_READ;
  zip->i_ptr = &zip->inbuf[0];
  zip->i_end = &zip->inbuf[read];

  return MSPACK_ERR_OK;
}

int mszipd_decompress(...)
{
  [...]
  do {
    READ_BITS(i, 8);
    if (i == 'C') state = 1;
    else if ((state == 1) && (i == 'K')) state = 2;
    else state = 0;
  } while (state != 2);
  [...]
}

Modification of the cffile_FolderOffset to 0xff in a CAB file can cause a 
read of zero, resulting in the infinite loop.

ClamAV is used in a number of mail gateway products. Successful 
exploitation requires an attacker to send a specially constructed CAB file 
through a mail gateway or personal anti-virus client utilizing the ClamAV 
scanning engine. The infinite loop will cause the ClamAV software to use 
all available processor resources, resulting in a denial of service or 
severe degradation to system performance. Remote exploitation can be 
achieved by sending a malicious file in an e-mail message or during an 
HTTP session.

CVE Information:
 <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-1922> 
CAN-2005-1922
 <http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-1923> 
CAN-2005-1923

Disclosure Timeline:
06/07/2005 - Initial vendor notification
06/08/2005 - Initial vendor response
06/29/2005 - Public disclosure


ADDITIONAL INFORMATION

The information has been provided by  <mailto:[email protected]> 
iDEFENSE.
The original article can be found at:  
<http://www.idefense.com/application/poi/display?id=275&type=vulnerabilities> http://www.idefense.com/application/poi/display?id=275&type=vulnerabilities,
 
<http://www.idefense.com/application/poi/display?id=276&type=vulnerabilities> http://www.idefense.com/application/poi/display?id=276&type=vulnerabilities



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