Re: libpq compression

I will preface this with that I am not a security guy and that also do
not know how the Zstd vompression works, so take any of what I say with
a grain of salt.

On 2/8/19 8:14 AM, Andres Freund wrote:> I think compression is pretty
useful, and I'm not convinced that the
> threat model underlying the attacks on SSL really apply to postgres.
I think only because it is usually harder to intercept traffic between
the application server and the database than between the we bbrowser and
the web server.

Imagine the following query which uses the session ID from the cookie to
check if the logged in user has access to a file.

SELECT may_download_file(session_id => $1, path => $2);

When the query with its parameters is compressed the compressed size
will depend on the similarity between the session ID and the requested
path (assuming Zstd works similar to DEFLATE), so by tricking the web
browser into making requests with specifically crafted paths while
monitoring the traffic between the web server and the database the
compressed request size can be use to hone in the session ID and steal
people's login sessions, just like the CRIME attack[1].

So while compression is a very useful feature I am worried that it also
opens application developers to a new set of security vulnerabilities
which they previously were protected from when compression was removed
from SSL.

1. https://en.wikipedia.org/wiki/CRIME

Andreas