Advisory 01/2004: 12 x Gaim remote overflows Jan 26 2004 08:44AM
Stefan Esser (s esser e-matters de)
e-matters GmbH

-= Security Advisory =-

Advisory: 12 x Gaim remote overflows
Release Date: 2004/01/26
Last Modified: 2004/01/26
Author: Stefan Esser [s.esser (at) e-matters (dot) de [email concealed]]

Application: Gaim <= 0.75
Severity: 12 vulnerabilities were found in the instant
messenger GAIM that allow remote compromise
Risk: Critical
Vendor Status: Vendor has fixed in CVS, but feels not ready for
release because of problems with HEAD
Reference: http://security.e-matters.de/advisories/012004.html


Gaim is a multi-protocol instant messaging client for Linux, BSD,
MacOS X, and Windows. It is compatible with AIM (Oscar and TOC
protocols), ICQ, MSN Messenger, Yahoo, IRC, Jabber, Gadu-Gadu,
and Zephyr networks. It is a very popular choice among the users
of instant messaging networks and especially in the community of
migrated windows users.

While developing a custom add-on, an integer overflow in the
handling of AIM DirectIM packets was revealed that could lead
to a remote compromise of the IM client. After disclosing this
bug to the vendor, they had to make a hurried release because
of a change in the Yahoo connection procedure that rendered
GAIM useless. Unfourtunately at the same time a closer look
onto the sourcecode revealed 11 more vulnerabilities.

The 12 identified problems range from simple standard stack
overflows, over heap overflows to an integer overflow that can
be abused to cause a heap overflow. Due to the nature of instant
messaging many of these bugs require man-in-the-middle attacks
between client and server. But the underlying protocols are
easy to implement and MIM attacks on ordinary TCP sessions is
a fairly simple task.

In combination with the latest kernel vulnerabilities or the
habit of users to work as root/administrator these bugs can
result in remote root compromises.


While auditing the Gaim source code the following 12
vulnerabilities were discovered:

Overflows in YMSG protocol (yahoo messenger) handler

01) Yahoo Octal-Encoding Decoder Overflow
02) Yahoo Octal-Encoding Decoder Out-Of-Bounds Overflow
03) Yahoo Web Cookie Parser Overflow
04) Yahoo Login Page Name Parser Overflow
05) Yahoo Login Page Value Parser Overflow
06) Yahoo Packet Parser Overflow

Overflows in oscar protocol (AIM) handler

07) AIM/Oscar DirectIM Integer Overflow

Overflows in utility functions
(called in various protocols)

08) Quoted Printable Decoder Overflow
09) Quoted Printable Decoder Out-Of-Bounds Overflow
10) URL Parser Function Overflow
11) Extract Info Field Function Overflow

Overflows that do not fit into
the other categories

12) HTTP Proxy Connect Overflow

Detailed Bug Description

[01 - Yahoo Octal-Encoding Decoder Overflow]
[02 - Yahoo Octal-Encoding Decoder Out-Of-Bounds Overflow]

When the Yahoo Messenger handler decodes an octal value for
email notification functions 2 different kind of overflows
can be triggered

Affected version: 0.75 (only)
File: gaim/src/protocols/yahoo/yahoo.c
Function: yahoo_decode()

static char *yahoo_decode(const char *text)
char *converted;
char *p, *n, *new;

n = new = g_malloc(strlen (text) + 1);

for (p = (char *)text; *p; p++, n++) {
if (*p == '\\') {
sscanf(p + 1, "%3o\n", (int *)n); <-------- [01]
p += 3; <--------------------------------- [02]
*n = *p;

*n = '\0';

The way sscanf is used, it will always write 4 bytes to the
allocated buffer. The author did not see the possibility of
malformed input like "\1" (the backslash is only a backslash) it
is possible to write 1-2 zero bytes over the buffer boundaries.
On linux this is exploitable like any heap off by one into the
malloc() chunks. The second vulnerability is that no matter how
many bytes sscanf() consumes it always increases the pointer
with assumed 4 bytes. This can result in overjumping the
terminating zero byte and with special prepared memory after
the string it is possible to overwrite the heap with an
arbitrary amount of bytes.

These bugs are counted as 2 because for most people [02] is not
obvious. As an example the vendor fixed only [01] first, because
my description was not good enough. Additionally the misuse of
sscanf() caused an incompatibility to all big endian platforms.

[03 - Yahoo Web Cookie Parser Overflow]

When parsing the cookies within the HTTP reply header of a
yahoo web connection a bufferoverflow can happen.

Affected version: <= 0.75
File: gaim/src/protocols/yahoo/yahoo.c
Function: yahoo_web_pending()

void yahoo_web_pending(gpointer data, gint source, ...
GaimConnection *gc = data;
GaimAccount *account = gaim_connection_get_account(gc);
struct yahoo_data *yd = gc->proto_data;
char buf[1024], buf2[256], *i = buf, *r = buf2;
int len, o = 0;

len = read(source, buf, sizeof(buf));
while ((i = strstr(i, "Set-Cookie: ")) && 0 < 2) {
i += strlen("Set-Cookie: ");
for (;*i != ';'; r++, i++) {
*r = *i;

Here all cookie data contained in the first 1024 byte of a
HTTP reply header is copied into a 256 byte buffer without
a size check. Because source and destination buffer are
both on the stack and stack layout will most probably
result in the smaller buffer overflowing into the smaller
one this bug is believed to be not exploitable with the
normal stack layout. Note also the typo in the while()
condition 0 < 2 which should be o < 2

[04 - Yahoo Login Page Name Parser Overflow]
[05 - Yahoo Login Page Value Parser Overflow]

When parsing the Yahoo Login Webpage the YMSG protocol overflows
stachbuffers if the webpage returns oversized values.

Affected version: <= 0.75
File: gaim/src/protocols/yahoo/yahoo.c
Function: yahoo_login_page_hash()

GHashTable *yahoo_login_page_hash(const char *buf,size_t len)
GHashTable *hash = g_hash_table_new_full(g_str_hash, g_s...
const char *c = buf;
char *d;
char name[64], value[64];
while ((c < (buf + len)) && (c = strstr(c, "<input "))) {
c = strstr(c, "name=\"") + strlen("name=\"");
for (d = name; *c!='"'; c++, d++) <----------- [04]
*d = *c; <---------/
*d = '\0';
d = strstr(c, "value=\"") + strlen("value=\"");
if (strchr(c, '>') < d)
for (c = d, d = value; *c!='"'; c++, d++) <--- [05]
*d = *c; <-----------------------------/
*d = '\0';
g_hash_table_insert(hash, g_strdup(name), g_strdup(value));
return hash;

The content of the yahoo login webpage is trusted although it
could be changed with a simple man-in-the-middle attack on the
HTTP session. name and value are filled directly from the page
without any kind of size check. This results in two independent
ways to overflow the stack.

[06 - Yahoo Packet Parser Overflow]

A Yahoo Messenger packet consist of a header and a list of keys
with their associated values. When reading an oversized keyname
a standard stackoverflow can be triggered. This is nost probably
the most dangerous discovered vulnerability because the nature
of the bug makes it very easy to exploit and additonally a TCP
man-in-the-middle attack is NOT needed. It is possible to send
a malicious YMSG packet to the yahoo server so that it will
be forwarded like any normal message.

Affected version: <= 0.75
File: gaim/src/protocols/yahoo/yahoo.c
Function: yahoo_packet_read()

static void yahoo_packet_read(struct yahoo_packet *pkt,
guchar *data, int len)
int pos = 0;

while (pos + 1 < len) {
char key[64], *value = NULL, *esc;
int accept;
int x;

struct yahoo_pair *pair = g_new0(struct yahoo_pair, 1);

x = 0;
while (pos + 1 < len) {
if (data[pos] == 0xc0 && data[pos + 1] == 0x80)
key[x++] = data[pos++]; <----------------- [06]
key[x] = 0;
pos += 2;

Everytime the YMSG handler receives a complete packet it will
give it this function to split it into its keys and values.
Because the keyname is copied without any kind of size check
into the key variable which is a 64 byte stackbuffer it is very
easy to exploit.
NOTE: This bug is also exploitable on systems with non executable
stacks, or stack overflow detections as long free() exploits are
possible on that platform,

[07 - AIM/Oscar DirectIM Integer Overflow]

Integer Overflow when allocating memory for a directIM packet
results in heap overflow. directIM is a client 2 client protocol
and therefore does not require a mim.

Affected version: <= 0.74
File: gaim/src/protocols/oscar/ft.c
Function: handlehdr_odc()

static int handlehdr_odc(aim_session_t *sess, aim_...
aim_frame_t fr;
int ret = 0;
aim_rxcallback_t userfunc;
fu32_t payloadlength;
fu16_t flags, encoding;
char *snptr = NULL;

fr.conn = conn;

/* AAA - ugly */
aim_bstream_setpos(bs, 20);
payloadlength = aimbs_get32(bs);


if (payloadlength) {
char *msg;

if (!(msg = calloc(1, payloadlength+1))) { <--- [07]
return -ENOMEM;

while (payloadlength - recvd) {
if (payloadlength - recvd >= 1024)
i = aim_recv(conn->fd, &msg[recvd], 1024);

Within this code snipset payloadlength is taken directly from the
network and passed to the calloc() function in an unsafe manner.

A user supplied payloadlength of UINT_MAX (0xffffffff) will cause
an integer overflow within the second parameter of calloc() and
therefore only allocate a 0 byte buffer. Please notice that this
bug is not an integer overflow due to the multiplication within
calloc() and therefore it is not catched by the recent security
patches to calloc() on different platforms. Please also note that
calloc(1, 0) will not return a NULL pointer but a pointer into
the legal heap on at least all tested platforms (f.e. linux, bsd)
On BSD systems this is configureable but it defaults to this
behaviour. After allocating the 0 byte buffer aim_recv() is called
repeatedly by the while loop to read and overwrite with up to 4GB
of data.

[08 - Quoted Printable Decoder Overflow]
[09 - Quoted Printable Decoder Out-Of-Bounds Overflow]

When the MIME decoder decosed a quoted printable encoded string
for email notification 2 different kind of overflows can be

Affected version: 0.75 (only)
File: gaim/src/util.c
Function: quotedp_decode()

gaim_quotedp_decode(const char *str, char **ret_str, int ...
char *p, *n, *new;

n = new = g_malloc(strlen (str) + 1);

for (p = (char *)str; *p; p++, n++) {
if (*p == '=') {
sscanf(p + 1, "%2x\n", (int *)n); <-------- [08]
p += 2; <--------------------------------- [09]
else if (*p == '_')
*n = ' ';
*n = *p;

*n = '\0';

Because these bugs are very similar to [01] and [02] only the
vulnerable code snipset is shown here. For an explanation read
the yahoo_decode() vulnerability description.

[10 - URL Parser Function Overflow]

At various placed this utility function is used to split an
url into its parts. Because temporary fixed size stackbuffers
are used in an unsafe way a standard stackoverflow can be

Affected version: <= 0.75
File: gaim/src/util.c
Function: gaim_url_parse()

gaim_url_parse(const char *url, char **ret_host,
int *ret_port, char **ret_path)
char scan_info[255];
char port_str[5];
int f;
const char *turl;
char host[256], path[256];
int port = 0;
/* hyphen at end includes it in control set */
static char addr_ctrl[] = "A-Za-z0-9.-";
static char port_ctrl[] = "0-9";
static char page_ctrl[] = "A-Za-z0-9.~_/:*!@&%%?=+^-";

g_snprintf(scan_info, sizeof(scan_info),
"%%[%s]:%%[%s]/%%[%s]", addr_ctrl,
port_ctrl, page_ct

f = sscanf(url, scan_info, host, port_str, path); <-- [10]

Here sscanf() is again used in an unsafe manner. When this
function is called with an oversized url, which can be triggered
from several protocol handlers in different ways sscanf() will
overwrite the stackbuffers host and path. The problem at this
point is, that it is only possible to overwrite the buffers with
a limited characterset which makes exploitation tricky.

[11 - Extract Info Field Function Overflow]

At various places this utility function is called to copy the
data between 2 tokens into a fixed size stackbuffer without a
size check.

Affected version: <= 0.74
File: gaim/src/util.c
Function: gaim_markup_extract_info_field()

const char *p, *q;
char buf[1024];

p = strstr(str, start_token);
p += strlen(start_token) + skip;
q = strstr(p, end_token);

if (q != NULL && (!no_value_token ||
(no_value_token && strncmp(p, no_value

if (is_link)
strcat(dest_buffer, "<br><a href=\"");
memcpy(buf, p, q - p); <---------------------- [11]
buf[q - p] = '\0';

Here it is obvious that if q - p is bigger than 1024 bytes
memcpy() will overwrite the stack which will result in a
standard stack overflow. At the moment this routine is
called from within the get_user_info functions of the MSN
and YMSG protocol handlers.

[12 - HTTP Proxy Connect Overflow]

When Gaim is setup to use a HTTP proxy for connecting to the
server a malicious HTTP proxy can exploit it.

Affected version: <= 0.75
File: gaim/src/proxy.c
Function: http_canread()

static void
http_canread(gpointer data, gint source, GaimInputCondit...
int nlc = 0;
int pos = 0;
int minor, major, status, error=0;
struct PHB *phb = data;
char inputline[8192], *p;


while ((nlc != 2) &&
(read(source, &inputline[pos++], 1) == 1)) {
if (inputline[pos - 1] == '\n')
else if (inputline[pos - 1] != '\r')
nlc = 0;
inputline[pos] = '\0';

Here the author never thought about the possibility that a
proxy server could be malicious. The inputline is read into
the 8192 byte buffer byte after byte until a double \r\n is
found. Because there is no size check at all the buffer will
overflow as soon the proxy sends more than 8192 bytes in a
line. This bug is exploitable even if stack overwrite
protections are in place because it is possible to overwrite
the pointer phb which points to a struct that contains a
callback function which is later called in the function.
By overwriting the pointer and so controlling the callback
function pointer it is possible to gain control over the
instruction pointer before the function is left.

Proof of Concept:

e-matters is not going to release exploit for any of the these
vulnerability to the public.

CVE Information:

The Common Vulnerabilities and Exposures project (cve.mitre.org)
has assigned the following names to these issues.

CAN-2004-0005: version 0.75 only, buffer overflows:

[01 - Yahoo Octal-Encoding Decoder Overflow]
[02 - Yahoo Octal-Encoding Decoder Out-Of-Bounds Overflow]
[08 - Quoted Printable Decoder Overflow]
[09 - Quoted Printable Decoder Out-Of-Bounds Overflow]

CAN-2004-0006: 0.75 and earlier, buffer overflows:

[03 - Yahoo Web Cookie Parser Overflow]
[04 - Yahoo Login Page Name Parser Overflow]
[05 - Yahoo Login Page Value Parser Overflow]
[06 - Yahoo Packet Parser Overflow]
[10 - URL Parser Function Overflow]
[12 - HTTP Proxy Connect Overflow]

CAN-2004-0007: 0.74 and earlier, buffer overflows:

[11 - Extract Info Field Function Overflow]

CAN-2004-0008: 0.74 and earlier, integer overflow:

[07 - AIM/Oscar DirectIM Integer Overflow]

Disclosure Timeline:

04. January 2004 - The Oscar filetransfer bug was sent to the
Gaim vendor by email. Within an hour the bug
was fixed within the CVS
10. January 2004 - Gaim vendor released version 0.75 because of
a Yahoo protocol change problem(?)
Some freetime allowed deeper analysis of the
new version. This revealed more bugs: 1 fixed
in 0.75, some new in 0.75 and some old which
are still in 0.75. All these bugs were again
mailed to the vendor
15. January 2004 - Vendor was contacted with a patch because
they had not fixed the bugs yet. Our Patch
was applied in the same night
16. January 2004 - Vendor-sec was contacted to coordinate the
disclosure process. Vendor was asked by email
when 0.76 is about to come out and that this
should be as soon as possible because the
bugfixes were visible in their CVS with
explicit commit messaged. No response to this
mail until today
23. January 2004 - Vendor was notified about public disclosure
at the 26th.
25. January 2004 - Notification by the vendor that gaim 0.76
releasedate is not planned yet.
26. January 2004 - Public Disclosure


Because there is no official new version out yet, you can download
a diff against version 0.75 from


This patch was done by the FreeBSD security team. It is different
from the official patches in the Gaim CVS. We suggest that you
upgrade as soon as possible, because the explicit commit message
into the official CVS tree seems to have leaked. At least it was
reported to us that a link to the message on the sourceforge
WebCVS was pasted into an IRC channel.



pub 1024D/75E7AAD6 2002-02-26 e-matters GmbH - Securityteam
Key fingerprint = 43DD 843C FAB9 832A E5AB CAEB 81F2 8110 75E7 AAD6

Copyright 2004 Stefan Esser. All rights reserved.


Stefan Esser s.esser (at) e-matters (dot) de [email concealed]
e-matters Security http://security.e-matters.de/

GPG-Key gpg --keyserver pgp.mit.edu --recv-key 0xCF6CAE69
Key fingerprint B418 B290 ACC0 C8E5 8292 8B72 D6B0 7704 CF6C AE69
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