[tor-relays] Long-term effect of Heartbleed on Tor

[Tom van der Woerdt]

I just had a quick look at the code that caused the bug (good overview 
at 
http://blog.existentialize.com/diagnosis-of-the-openssl-heartbleed-bug.html). 
The problem is that a length (unsigned short) is read from the incoming 
data but then it doesn't check whether there's actually enough data to 
read all of it.

The only way I can think of to check this is to manipulate the payload 
length. Making this length something lower than what we actually send 
should return in only a part of the original data being sent back. Of 
course this is behavior in both the bad and good versions, so we can't 
check it that way. We could also make the length field something higher 
than what we actually send, but this would mean getting back data.

*However*, if there's a way to specify the data it sends back, that 
wouldn't be a problem (I'm no legal specialist though). I have not yet 
tested my theory, but sending a few extra bytes in the heartbeat message 
(and of course incrementing 'length' in the 'ssl3_record_st' struct) 
should do that. It would allow causing the server to return data the 
client sent. If it's not sent back, the server isn't vulnerable. No 
random memory is read as the server did in fact allocate the memory, 
it's simply not supposed to use it.

Just a thought, maybe someone with more knowledge of these things can 
confirm it?

Tom


Alexander Dietrich schreef op 09/04/14 21:07:
> According to Qualys, they have developed a test that "verifies the 
> problem without retrieving any bytes from the server, other than the 
> bytes we send in the heartbeat request":
> https://community.qualys.com/blogs/securitylabs/2014/04/08/ssl-labs-test-for-the-heartbleed-attack 
>
>
> Best regards,
> Alexander
> ---
> PGP Key: 0xC55A356B | https://dietrich.cx/pgp
>
> On 2014-04-09 20:51, Paul Pearce wrote:
>>> * Should authorities scan for bad OpenSSL versions and force their 
>>> weight
>>> down to 20?
>>
>> I'd be interested in hearing people's thoughts on how to do such
>> scanning ethically (and perhaps legally). I was under the impression
>> the only way to do this right now is to actually trigger the bounds
>> bug and export some quantity (at least 1 byte) of memory from the
>> vulnerable machine.
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