CVE-2015-2721

Mozilla Network Security Services (NSS) anterior a 3.19, utilizado en Mozilla Firefox anterior a 39.0, Firefox ESR 31.x anterior a 31.8 y 38.x anterior a 38.1, Thunderbird anterior a 38.1, y otros productos, no determina correctamente las transiciones de estado para la máquina de estados TLS, lo que permite a atacantes man-in-the-middle derrotar los mecanismos de protección criptográfica mediante el bloqueo de mensajes, tal y como fue demostrado mediante la eliminación de una propiedad de confidencialidad adelantada mediante el bloqueo de un mensaje ServerKeyExchange, también conocido como un problema de 'SMACK SKIP-TLS' .

It was found that NSS permitted skipping of the ServerKeyExchange packet during a handshake involving ECDHE (Elliptic Curve Diffie-Hellman key Exchange). A remote attacker could use this flaw to bypass the forward-secrecy of a TLS/SSL connection.

USN-2656-1 fixed vulnerabilities in Firefox for Ubuntu 14.04 LTS and later releases. This update provides the corresponding update for Ubuntu 12.04 LTS. Karthikeyan Bhargavan discovered that NSS incorrectly handled state transitions for the TLS state machine. If a remote attacker were able to perform a man-in-the-middle attack, this flaw could be exploited to skip the ServerKeyExchange message and remove the forward-secrecy property. Looben Yan discovered 2 use-after-free issues when using XMLHttpRequest in some circumstances. If a user were tricked in to opening a specially crafted website, an attacker could potentially exploit these to cause a denial of service via application crash, or execute arbitrary code with the privileges of the user invoking Firefox. Various other issues were also addressed.