Re: ssh-1.2.27 remote buffer overflow - exploitable

Daniel Jacobowitz (drowFALSE.ORG)
Tue, 9 Nov 1999 11:24:17 -0500

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On Tue, Nov 09, 1999 at 01:48:53AM -0000, Frank wrote:
> This is submitted to the Freebsd bug tracking system, although there
> are doubtless other vendors who leave this package, despite the
> existence of the ssh-2.X. While Debian appears to be immune, I was
> able to crash my ssh daemon (much to my dismay), and there appears
> the potential to execute arbitrary code, as long as you encrypt it
> first...
>
> Here is the freebsd report.. it describes the method to crash a
> remote Ssh daemon (lets hope you ran sshd from your xinetd, etc).
>
> http://www.freebsd.org/cgi/query-pr.cgi?pr=14749
>

And here's a patch. Not tested, as I don't use the rsaref glue on any
machine here.

Dan

/--------------------------------\ /--------------------------------\
| Daniel Jacobowitz |__| SCS Class of 2002 |
| Debian GNU/Linux Developer __ Carnegie Mellon University |
| dandebian.org | | dmj+andrew.cmu.edu |
\--------------------------------/ \--------------------------------/

--- rsaglue.c.orig Tue Nov 9 11:12:32 1999
+++ rsaglue.c Tue Nov 9 11:17:58 1999
-139,6 +139,10

   input_bits = mpz_sizeinbase(input, 2);
   input_len = (input_bits + 7) / 8;
+ if(input_bits > MAX_RSA_MODULUS_BITS)
+ fatal("Attempted to encrypt a block too large (%d bits, %d max) (malicious?).",
+ input_bits, MAX_RSA_MODULUS_BITS);
+
   gmp_to_rsaref(input_data, input_len, input);

   rsaref_public_key(&public_key, key);
-172,6 +176,10

   input_bits = mpz_sizeinbase(input, 2);
   input_len = (input_bits + 7) / 8;
+ if(input_bits > MAX_RSA_MODULUS_BITS)
+ fatal("Received session key too long (%d bits, %d max) (malicious?).",
+ input_bits, MAX_RSA_MODULUS_BITS);
+
   gmp_to_rsaref(input_data, input_len, input);

   rsaref_private_key(&private_key, key);

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