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List:       full-disclosure
Subject:    [FD] OpenSSL 1.1.0 remote client memory corruption
From:       Guido Vranken <guidovranken () gmail ! com>
Date:       2016-10-13 16:06:48
Message-ID: CAO5O-E+Mnk6DkT8_yHhnczS77gHVKzYiw_AKjTyG9OFi211_aw () mail ! gmail ! com
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Triggering this requires that the client sets a very large ALPN list
(several thousand bytes). This would be very unusual in a real-world
application. For this reason OpenSSL does not treat this as a security
vulnerability and I am inclined to agree with this decision. However, if an
attacker can somehow influence the ALPN list of an OpenSSL-enabled
application (perhaps through another vulnerability), the attacker can write
arbitrary data past OpenSSL's heap buffer.

openssl s_client -reconnect -status -alpn `python -c "import sys;
sys.stdout.write('x,'*4000+'x')"`

If the server sends a session ticket with a special length (16022 bytes),
the client will crash.

More technical details here:

https://guidovranken.wordpress.com/2016/10/13/openssl-1-1-0-remote-client-memory-corruption-in-ssl_add_clienthello_tlsext/


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