Based on writing the code to these checks, I think it would be good
for the CAB Forum to consider the following clarifications/changes:

1) for dNSname type GeneralNames, make sure implementers are aware
that the "preferred name synatx" in RFC1034  does not allow a trailing
period on a Domain Name ( is not valid) and are aware that
leading and trailing whitespace is not allowed.

2) For commonName attributes in subject DNs, clarify that they can only contain:
- IPv4 address in dotted-decimal notation (specified as IPv4address
from section 3.2.2 of RFC 3986)
- IPv6 address in coloned-hexadecimal notation (specified as
IPv6address from section 3.2.2 of RFC 3986)
- Fully Qualified Domain Name or Wildcard Domain Name in the
"preferred name syntax" (specified by Section 3.5 of RFC1034 and as
modified by Section 2.1 of RFC1123)
- Fully Qualified Domain Name or Wildcard Domain Name in containing
u-labels (as specified in RFC 5890)

3) Forbid commonName attributes in subject DNs from containing a Fully
Qualified Domain Name or Wildcard Domain Name that contains both one
or more u-labels and one or more a-labels (as specified in RFC 5890).

4) Forbid all IP addresses that are listed in
or in
except those with global = true.

If the Forum decides to allow an exception to RFC 5280 to permit IP
address strings in dNSName general names, then require the same format
as allowed for common names.


On Tue, Nov 17, 2015 at 1:17 PM, Jeremy Rowley
<> wrote:
> They were until Feb 2013 :)
> Sure - let's discuss these issues at the CAB Forum. Based on the spreadsheet, 
> I'm pretty sure lots of CAs would like to re-address the elimination of all 
> SANs except iPAddress and dNSANames.
> -----Original Message-----
> From: Rob Stradling []
> Sent: Tuesday, November 17, 2015 2:12 PM
> To: Jeremy Rowley
> Cc: Richard Wang;; Peter Bowen; 
> Peter Gutmann
> Subject: Re: [FORGED] Name issues in public certificates
> On 17/11/15 18:27, Jeremy Rowley wrote:
>> Encoding an IP Address in a dNSName is not permitted by the BRs.  This is 
>> what Peter's "_ipv4_not_allowed_here" rule refers to, IIUC.
>> [JR] I suppose that is true under but how would you get the 
>> browsers to work back then? Chrome and IE did not process ipAddress properly.
> Jeremy, I don't recall any clause in the BRs that permits CAs to ignore 
> requirements that they or their customers don't like.
> They are not Baseline Suggestions! ;-)
> If (whilst the BRs have been in force) there's been a perceived need to 
> encode IP addresses in dNSName fields, then don't you think that the correct 
> thing to do would've been to take the matter to CABForum and seek to update 
> the BRs so that this practice is permitted?
>> Jeremy
>>> Regards,
>>> Richard
>>> -----Original Message-----
>>> From: dev-security-policy
>>> [
>>> o
>>> rg] On Behalf Of Rob Stradling
>>> Sent: Tuesday, November 17, 2015 9:32 PM
>>> To: Peter Gutmann <>; Peter Bowen
>>> <>;
>>> Subject: Re: [FORGED] Name issues in public certificates
>>> On 17/11/15 08:25, Peter Gutmann wrote:
>>>> Peter Bowen <> writes:
>>>>> There are a couple of rules that may create false positives, so
>>>>> please don't assume every certificate on the sheet is problematic.
>>>> That's still pretty scary, nearly 50,000 names from a who's-who of
>>>> commercial CAs.  Yet more evidence that, like the output from the
>>>> EFF SSL Observatory, we need independent assessment of browser PKI
>>>> rather than self-certification ("we define ourselves to be in full
>>>> compliance with everything we need to be compliant with, as far as we can 
>>>> tell").
>>>> Peter.
>>> Peter (G),
>>> I fully agree that independent assessment is useful, but independent
>>> assessments need to be assessed too (preferably before the press
>>> start quoting soundbites! :-) )
>>> Peter (B),
>>> Thanks for doing this report.  There are definitely some interesting 
>>> findings.
>>> However, I would like to discuss several classes of (what I think
>>> are) false positives that cover a significant number of the "anomalies" 
>>> you've found:
>>>      - RFC5280 sections 7.2 and 7.3 do indeed talk about the need for
>>> dNSNames, domainComponents, etc, to only contain ASCII data.
>>> However, your report also flags Subject CNs with non-ASCII data -
>>> AFAICT, this is permitted by both
>>> RFC5280 and the BRs.  It is common practice to put the "xn--" ASCII
>>> string in a dNSName and the UTF-8 string in the Subject CN.
>>>      - You wanted to check that "public CAs were following the
>>> CA/Browser Forum baseline requirements" when issuing certs.  However,
>>> some of the certs in your report were issued before any of the
>>> browsers / audit regimes demanded that public CAs be compliant with the BRs.
>>> Furthermore, some of the certs in your report were issued before the
>>> BRs even existed.
>>>      - You wanted to check "server auth certificates issued by public CAs".
>>> However, I see some Code Signing Certificates in your report.
>>> I'm pretty optimistic that all of the "anomalies" issued by Comodo's
>>> CA system (except for the 8 mentioned in our recent incident report)
>>> will be found to fall into these categories, although I haven't done
>>> an exhaustive analysis yet.  If there are any other "anomalies",
>>> they're a bit lost in the noise at present!
> --
> Rob Stradling
> Senior Research & Development Scientist
> COMODO - Creating Trust Online
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