TSIG authentication bypass through signature forgery in ISC BIND

[Nytro]

TSIG authentication bypass through signature forgery in ISC BIND

 

Synacktiv experts discovered a flaw within the TSIG protocol implementation in BIND that would allow an

attacker knowing a valid key name to bypass the TSIG authentication on zone updates, notify and transfers

operations.

This issue is due to the fact that when a wrong TSIG digest length is provided (aka the digest doesn’t have

a length that matches the hash algorithm used), the server still signs its answer by using the provided

digest as a prefix. This allows an attacker to forge the signature of a valid request, hence bypassing the

TSIG authentication.

 

Download: http://www.synacktiv.ninja/ressources/CVE-2017-3143_BIND9_TSIG_dynamic_updates_vulnerability_Synacktiv.pdf