Title: tinc Weak Salt Length Traffic Pattern Analysis Vulnerability
Severity: MODERATE
Description:
tinc is a Virtual Private Network (VPN) daemon designed for Linux and Unix based systems. It acts as a tunnel for a network interface, and embeds all communication into a sequence of encrypted UDP packets. This allows private network communication to occur through a larger network. tinc uses blowfish in cipher block chaining (CBC) mode to encrypt packets. The secret key is shared via a PKI-style handshake during the authentication process between two tinc daemons.
In order to avoid the detection of regular traffic patterns (specifically, the ability to recognize repeated, identical packets), tinc prepends a two byte random salt to each packet before it is encrypted. While this is sufficient for many applications, under some circumstances traffic analysis may still be possible.
Due to the birthday paradox, the number of identical packets (excluding the random salt) that must be sent before a collision in salt values is likely is much less than the 65536 values possible. In fact, if approximately 2-300 identical packets are sent, a salt collision is over 50% probable.
This vulnerability is unlikely to affect most applications. For example, the TCP protocol includes a random sequence number, which may prevent a large number of completely identical packets from ever being transmitted. However, applications using a protocol such as UDP may be vulnerable.
Affected Products:
- tinc tinc 1.0.0pre3
- tinc tinc 1.0.0pre4
References:
- tinc: tinc Homepage
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