cyberstrikeus CIS 4.1 — Use TSIG Keys 256 Bits in Length
Profile Applicability
- Level 1 - Authoritative Name Server
- Level 1 - Caching Only Name Server
Description
The TSIG secret keys used by the name server should be generated from a good source of entropy and should be at least 256 bits in length.
Rationale
Weak cryptographic keys may allow cryptographic attacks to discover the key value, through repeated guesses. A strong HMAC key requires a good source of entropy and at least 256 bits in length.
Impact
None noted.
Audit Procedure
To check if the secret key is at least 256 bits long before encoding then the base64 encoded value should be 44 characters long or longer with the padding and a trailing =. To easily count the number of characters, copy the key value into the quoted value in the command below.
$ echo -n "ezoZopbE4Q73HShuFYlf3FRvLWjtNXI5fd0TeQAYOug=" | wc -c
44
Remediation
For remediation, replace any keys which are too short with a securely generated key with a length of 256 or 512. The dnssec-keygen command below can be used to generate a key.
$ dnssec-keygen -a HMAC-SHA256 -b 256 -n HOST ns1-ns2.cisecurity.org.
$ cat Kns1-ns2.cisecurity.org.+163+21730.key
ns1-ns2.cisecurity.org. IN KEY 512 3 163
ezoZopbE4Q73HShuFYlf3FRvLWjtNXI5fd0TeQAYOug=
Default Value
The rndc key is generated as 128 bits during bind-utils package install, while the nsupdate session key is dynamically generated with a length of 256 bits.
References
None listed.
CIS Controls
| Controls Version | Control | IG 1 | IG 2 | IG 3 |
|---|---|---|---|---|
| v6 | 14.2 - Encrypt All Sensitive Information Over Less-trusted Networks | Y | Y | Y |
MITRE ATT&CK Mappings
| Tactic | Technique |
|---|---|
| Credential Access | T1110 - Brute Force |
| Lateral Movement | T1557 - Adversary-in-the-Middle |
Profile
- Level 1 - Authoritative Name Server
- Level 1 - Caching Only Name Server