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Two Exploitable Overflows in PINE

09.10.03

BACKGROUND

PINE (The Program for Internet News & Email) is a popular e-mail client shipped with many Linux and Unix distributions. It was developed at the University of Washington; more information is available at http://www.washington.edu/pine/.

DESCRIPTION

PINE contains two exploitable vulnerabilities that can be triggered when a victim opens a specially crafted email sent by an attacker.

- --- Vulnerability 1: Buffer Overflow ---

A remotely exploitable buffer overflow exists within the parsing of the message/external-body type attribute name/value pairs. Failure to check that the length of the longest attribute is less than the space available allows a maliciously formed e-mail message to overwrite control structures. Careful modification of these values allows arbitrary code execution. However, exploitation requires knowledge of the targeted version of PINE.

A 20kb character array is declared as:

headers.h:
#define SIZEOF_20KBUF (20480)
pine.c: char tmp_20k_buf[SIZEOF_20KBUF];

The tmp_20k_buf[] array is stored within the .bss section and referenced with a character pointer 'd'.  The overflow occurs within the following snippet of code from the display_parameters() routine in mailview.c:

d = tmp_20k_buf;
if(parmlist = rfc2231_newparmlist(params)){
    while(rfc2231_list_params(parmlist) && d < tmp_20k_buf + 10000){
        sprintf(d, "%-*s: %sn", longest, parmlist->attrib,
                parmlist->value ? strsquish(tmp_20k_buf + 11000, parmlist->value, 100)
                : "");
        d += strlen(d);
    }

Starting at 'd', the code adds spaces to the left of the string as padding to make the total length of the parameter attribute string equal to that of the 'longest'. Later displaying the Attribute name/value pairs.

Example:

Access-Type: ftp
        URL: ftp://localhost/pub/interesting.ps

Supplying any attribute name that is over 20kb in length will overflow the buffer, eventually allowing for arbitrary code execution.

- --- Vulnerability 2: Integer Overflow ---

A remotely exploitable integer overflow exists in the parsing of e-mail headers, allowing for arbitrary code execution upon the opening of a malicious e-mail. The vulnerability exists within the rfc2231_get_param() routine found in the strings.c file. A character array of size 64 is declared:

#define RFC2231_MAX 64
...
char *pieces[RFC2231_MAX];
and indexed by the signed integer variable 'n':
if(n < RFC2231_MAX){
    pieces[n] = parms->value;

The variable 'n' is attacker-controlled and can be set to contain a negative value that satisfies the if statement yet references an out-of-bounds index within the pieces[] array. Arbitrary code execution is possible by storing assembly code within the parms->value structure and writing beyond the 64-byte character array, thereby overwriting the stored instruction pointer on the stack.

ANALYSIS

If an attacker were to socially engineer a PINE user into opening a malformed e-mail message, arbitrary code embedded within can then run with privileges of the currently logged on user. It would be trivial for this exploit to be fashioned into a worm, targeting e-mail addresses found in any readable text files (inbox, etc.).

DETECTION

PINE 4.56 and earlier is vulnerable.

VENDOR RESPONSE

PINE 4.58, which fixes both of these issues, is available at http://www.washington.edu/pine/getpine/.

CVE INFORMATION

The Mitre Corp.'s Common Vulnerabilities and Exposures (CVE) Project has assigned the following identification numbers to these issues:

CAN-2003-0720: Vulnerability 1 - PINE buffer overflow in its handling of the 'message/external-body' type.
CAN-2003-0721: Vulnerability 2 - PINE integer overflow in MIME header parsing.

DISCLOSURE TIMELINE

08/15/2003                   Issues acquired by iDEFENSE
08/25/2003                   Issues disclosed to pine@cac.washington.edu
08/25/2003                   Response from Mark Crispin, University of Washington
08/26/2003                   Issues disclosed to iDEFENSE clients
09/04/2003                   Issues disclosed to Linux vendors: vendor-sec@lst.de
09/10/2003                   Coordinated Public Disclosure

CREDIT

zen-parse (zen-parse@gmx.net) discovered these vulnerabilities.