How Many SANs are Insane?
x509 certificates, as they are used for TLS, can include multiple "Subject Alternative Names" (SANs) to be used with various websites. Experimenting with numerous ways to detect TLS anomalies, I looked at my Zeek x509 logs to summarize how many names are present in certificates.
My Zeek logs are stored in JSON format to make it easier to send them to Elasticsearch. But I also prefer the jq over the zeek native tool zeek-cut (personal preference).
I used this command line to summarize the logs:
zcat x509.log | jq '."san.dns" | length' | sort | uniq -c | sort -n
Based on this methodology, the maximum number of SANs per certificate is close to 500, but most are using 100 hostnames or less.
But the real question: What is normal?
It turns out there is no real "hard" limit. The RFCs leave it up to the implementation to define how many SANs to allow [1]. Different certificate authorities implement different limits:
Let's Encrypt [2] , GoDaddy[3]: 100
Comodo[4]: 1,000 (some older references appear to state 2,000 are allowed)
So, in short: it appears that 100 is "safe." For larger numbers, you may run into implementation-specific issues.
]1] https://datatracker.ietf.org/doc/html/rfc5280#section-4.2.1.6
[2] https://letsencrypt.org/docs/rate-limits/
[3] https://www.godaddy.com/web-security/multi-domain-san-ssl-certificat
[4] https://comodosslstore.com/comodo-mdc-ssl.aspx
---
Johannes B. Ullrich, Ph.D. , Dean of Research, SANS.edu
Twitter|
Comments
www
Nov 17th 2022
6 months ago
EEW
Nov 17th 2022
6 months ago
qwq
Nov 17th 2022
6 months ago
mashood
Nov 17th 2022
6 months ago
isc.sans.edu
Nov 23rd 2022
6 months ago
isc.sans.edu
Nov 23rd 2022
6 months ago
isc.sans.edu
Dec 3rd 2022
6 months ago
isc.sans.edu
Dec 3rd 2022
6 months ago
<a hreaf="https://technolytical.com/">the social network</a> is described as follows because they respect your privacy and keep your data secure. The social networks are not interested in collecting data about you. They don't care about what you're doing, or what you like. They don't want to know who you talk to, or where you go.
<a hreaf="https://technolytical.com/">the social network</a> is not interested in collecting data about you. They don't care about what you're doing, or what you like. They don't want to know who you talk to, or where you go. The social networks only collect the minimum amount of information required for the service that they provide. Your personal information is kept private, and is never shared with other companies without your permission
isc.sans.edu
Dec 26th 2022
5 months ago
isc.sans.edu
Dec 26th 2022
5 months ago