[openssl-dev] Fwd: CVE-2014-8730 TLS CBC Incorrect Padding Abuse Vulnerability

[Kurt Roeckx]

On Wed, Feb 03, 2016 at 05:11:34PM +0530, Shyamal Bhowmik wrote:
> 
>     /* enc_err is:
>      * 0: (in non-constant time) if the record is publically invalid.
>      * 1: if the padding is valid
>      * -1: if the padding is invalid */
>     if (enc_err == 0)
>         {
>         al=SSL_AD_DECRYPTION_FAILED;
>         SSLerr(SSL_F_SSL3_GET_RECORD,SSL_R_BLOCK_CIPHER_PAD_IS_WRONG);
>         goto f_err;
>         }
> 
> As seen from above, error is thrown only for 0 return value and -1 return
> value is not handled. So if i change the code  if (enc_err == 0)  to  if
> (enc_err <= 0) will solve my problem?

If you change that to <= 0 you will introduce a security problem
by leaking timing information.  There is an other check for < 0
below.

> There was no specific way to reproduce this issue and it was seen very
> sporadically.

I'm not sure what you're trying to fix, but if you're getting
padding it's also possible that you actually received a padding
error.

This also doesn't seem to have anything to do with CVE-2014-8730
which we weren't vulnerable to, as you actually explained
yourself.


Kurt