Researchers at Google have discovered a flaw in SSL 3 that allows "the plaintext of secure connections to be calculated by a network attacker." The vulnerability, known as POODLE (Padding Oracle On Downgraded Legacy Extension), is a form of man-in-the-middle attack, in which the attacker injects malicious JavaScript into the victim's browser. The attack, which is especially dangerous for an insecure wireless network such as a coffee house or other public space, results in information disclosure. For instance, the attacker can obtain session cookies from the target browser and use them to access the victim's online accounts.
SSL 3 is over 18 years old, and has long since been deprecated in favor of more advanced technologies, such as the heir-apparent TLS protocol, which is now the recommended replacement for SSL. The real problem is that browsers and servers are often configured to negotiate an encryption protocol. If the highest level protocol isn't available, the server will allow a connection with a less secure alternative. The attacker can thus coax the target to use SSL 3 even if more secure options are available.
The POODLE problem is not something that is easily patched, and, given the fact that SSL 3 is obsolete anyway, experts are advising users,admins, and developers to disable it. Mozilla has announced that SSL 3 will be disabled by default in the Firefox 34 release, which is due in November.
According to the post at the Google Online Security blog, "...our recommended response is to support TLS_FALLBACK_SCSV. This is a mechanism that solves the problems caused by retrying failed connections and thus prevents attackers from inducing browsers to use SSL 3.0. It also prevents downgrades from TLS 1.2 to 1.1 or 1.0 and so may help prevent future attacks." The TLS_FALLBACK_SCSV indicator was created by Google and implemented for Chrome browsers. Mozilla has announced that it will implement TLS_FALLBACK_SCSV in Firefox in early 2015.