Re: Certificate validation vulnerability in Git

On Mon, Feb 25, 2013 at 8:46 AM, Jeff King [off-list ref] wrote:

On Sun, Feb 24, 2013 at 11:01:50PM +0530, Zubin Mithra wrote:

quoted

There seems to be a security issue in the way git uses openssl for
certificate validation. Similar occurrences have been found and
documented in other open source projects, the research can be found at
[1].

-=========]
- imap-send.c

Line 307

 307   ret = SSL_connect(sock->ssl);
 308   if (ret <= 0) {
 309     socket_perror("SSL_connect", sock, ret);
 310     return -1;
 311   }
 312

Certificate validation errors are signaled either through return
values of SSL_connect or by setting internal flags. The internal flags
need to be checked using the SSL_get_verify_result function. This is
not performed.

I'm not sure what you mean. We use SSL_CTX_set_verify to turn on peer
certificate verification, which will cause SSL_connect to return
failure if the certificate signature cannot be traced back to a CA cert
from our local store.

Is there some case where this does not happen properly? If so, can you
give an example? The paper you referenced says only that there are some
special cases where SSL_connect does not notice the error, but then
gives an example where the application does not turn on SSL_VERIFY_PEER.
But git does. Are there are other cases that SSL_VERIFY_PEER does not
handle?

Indeed -- it appears that I was mistaken. I had a quick look at the
openssl source code and it does seem that SSL_VERIFY_PEER is
equivalent to SSL_get_verify_result.

Thank you for your time!

- Zubin

There is a _different_ problem not handled by the code you show above,
which is that SSL_connect does not verify that the hostname we connected
to matches the signed certificate. But that was fixed already by b62fb07
(imap-send: the subject of SSL certificate must match the host,
2013-02-15), which is in git v1.8.1.4.

-Peff