SSLv3 Padding Oracle On Downgraded Legacy Encryption Vulnerability (POODLE)
Medium Nessus Plugin ID 78479
Synopsis
It is possible to obtain sensitive information from the remote host
with SSL/TLS-enabled services.
Description
The remote host is affected by a man-in-the-middle (MitM) information
disclosure vulnerability known as POODLE. The vulnerability is due to
the way SSL 3.0 handles padding bytes when decrypting messages
encrypted using block ciphers in cipher block chaining (CBC) mode.
MitM attackers can decrypt a selected byte of a cipher text in as few
as 256 tries if they are able to force a victim application to
repeatedly send the same data over newly created SSL 3.0 connections.
As long as a client and service both support SSLv3, a connection can
be 'rolled back' to SSLv3, even if TLSv1 or newer is supported by the
client and service.
The TLS Fallback SCSV mechanism prevents 'version rollback' attacks
without impacting legacy clients; however, it can only protect
connections when the client and service support the mechanism. Sites
that cannot disable SSLv3 immediately should enable this mechanism.
This is a vulnerability in the SSLv3 specification, not in any
particular SSL implementation. Disabling SSLv3 is the only way to
completely mitigate the vulnerability.
Solution
Disable SSLv3.
Services that must support SSLv3 should enable the TLS Fallback SCSV
mechanism until SSLv3 can be disabled.