On November 10, CISA issued a blog
post called “TRANSFORMING THE VULNERABILITY MANAGEMENT LANDSCAPE”. It got a
lot of attention and widespread approval. It describes three techniques whose
implementation will, according to the post, lead to “more efficient, automated,
prioritized vulnerability management.” While these should be of interest to
both software (and intelligent device) suppliers and end users, the
recommendations are aimed primarily at the suppliers – since they need to take
the initiative in all three of these areas.
Since the third recommendation,
use of the new SSVC vulnerability categorization framework (which, not at all
coincidentally, is CVSS spelled backwards) isn’t closely related to the first two,
I’ll just focus on those two, although SSVC strikes me as a very good idea.
CISA’s first recommendation is
that software suppliers should “Publish machine-readable security advisories
based on the Common Security Advisory Framework (CSAF).” CSAF is currently on v2.0,
which is also its first versoin. CSAF is the replacement for the Common
Vulnerability Reporting Format (CVRF) version 1.2, which has been available
since 2017. CVRF was developed and maintained by the CSAF technical committee
of OASIS. I don’t know the full story, but at some point the committee presumably
decided that the new version they were contemplating was going to be so
different from CVRF that they should just name it after the committee. Sounds
like a smart move to me. After all, it’s all about branding.
Unfortunately, branding alone isn’t
enough when it comes to a machine-readable advisory format. You need two more
things. First, you need at least one software tool to create the advisories, for
use by suppliers who aren’t intimately familiar with the format. If you spend
five minutes looking through the CSAF format, I
think you’ll agree that it would take a lot of study for someone with no prior
knowledge of, or experience with, CSAF to create an advisory without the help
of a tool. Currently, the only available tool is Secvisogram, a CSAF editor (this was
also the only available tool when the VEX working group approved CSAF as the VEX
format in the spring of 2021). It will count brackets for you and perform
similar tasks, but you need a full understanding of the CSAF format in order to
use the tool to create a CSAF document.
There are a small number of mostly
very large organizations – including Oracle,
Cisco and Red Hat – that have announced support for CSAF 2.0. However, I could
only find actual CSAF files published by Red
Hat (and Red Hat labels the CSAF 2.0 format as “beta”, even though it was
finalized and approved more than a year ago). Presumably, those organizations
have been able to make the substantial investment of time required to create
CSAF advisories (I know that Cisco and Red Hat have been part of the CSAF technical
committee for years).
However, CISA’s blog post didn’t
limit its recommendations just to large, well-resourced companies. They clearly
want all software and device suppliers, large and small, to start issuing CSAF
vulnerability advisories. And this is where I see a problem: Expecting every supplier
of any size, large or small, to start creating CSAF advisories without having
to invest a huge amount of time learning the CSAF format requires a “CSAF for
Dummies” tool. I define this as a tool that prompts the user for the
information they want to represent in the advisory – the CVE or CVEs in question,
the affected products and versions, remediation advice for each affected version
(which might include a patch or upgrade, but might also include something else),
etc. To use the tool, the user shouldn’t need to understand the details of the
format; they should just be required to answer questions about what they want
in the advisory.
Currently, no such tool is available
for CSAF (one is under development, and
evidently has been for a long time); if a supplier wants to create CSAF
advisories now, they have to go Full Monty and learn CSAF well enough to be
able to use Secvisogram intelligently. And there are clearly a number of required
fields – like “product
name” (and the related concept of “product tree”) and “branches”
– whose meaning is anything but self-evident. Any supplier wishing to create CSAF
documents will need to have a good understanding of the huge number of options
available for creating these and other fields, as well as understand how versions
are represented, which is anything but straightforward.
Second, a machine-readable
advisory format, in order to be usable, requires tools that read the format.
And here the story is the same: There are no tools that read CSAF documents,
even a simple parser tool. There is a parser tool under development,
but that’s all. And frankly, a parser tool isn’t going to do end users a lot of
good. Since most medium-to-large organizations utilize some tool or tools to
manage vulnerabilities on their network (the tool may go under the name “scanner”,
“vulnerability management”, “configuration management”, “asset management”, and
probably other names as well), just parsing a CSAF file so that it’s readable
by ordinary humans doesn’t get the information into their vulnerability
management tool, where it’s needed. At the moment, the user is going to have to
key the information in by hand, unless they’ve created their own tool to do
this.
You probably get the idea: CSAF is
a machine-readable vulnerability reporting format, but currently no machine can
create or read CSAF documents – which raises the question what “machine
readable” means in practice. If CSAF 2.0 had just been recently released, I wouldn’t
be too bothered by this fact. Indeed, I wasn’t bothered a year ago that there
weren’t any tools for it, since it was then only three months since CSAF 2.0
had been approved (although it had been under development for at least a couple
of years).
But to be honest, the fact that it’s
a year later and there still aren’t tools available for producing or utilizing CSAF
documents makes me wonder why that’s the case and when this situation will
change. The VEX working group has been repeatedly assured that such tools are
under development (as we were 18 months ago, when we decided to base the VEX
format on CSAF); and it’s certainly true that they’re under development. But I
won’t recommend that any software supplier even start learning to create CSAF
documents until someone can provide me a firm date by which a CSAF creation tool
will be ready (and the date had better be before say July 1, 2023. Anything beyond
that isn’t a firm date; it’s a wish and a prayer).
Of course, it still won’t help
when there’s a CSAF creation tool, if there aren’t also CSAF consumption tools.
And those need to be something more than a parser, as described above. But I’ll
cut CSAF some slack: If there’s a parser ready by next July 1 along with a CSAF
production tool, I’m willing to stipulate that it might not take a huge
additional effort to put together the required interfaces to vulnerability management
tools (in fact, the tool vendors themselves might create them). So, by the end
of 2023, end user organizations might be able to actually utilize CSAF
advisories, if the production and parser tools are ready by July 1.
Getting back to the CISA blog
post, it seems clear that CISA should never have advised that suppliers start
putting out CSAF vulnerability advisories without also warning them that a)
they need to be prepared to invest a lot of time learning the CSAF format, and
b) they have to understand that currently no end user organization will be able
to do anything with the advisories when they get them.
CISA’s second recommendation was “Use
Vulnerability Exploitability eXchange (VEX) to communicate whether a product is
affected by a vulnerability and enable prioritized vulnerability response”. So
how about this? Are there tools to produce and utilize VEX documents?
Fortunately, the picture is much brighter there. There is at least one open
source tool now, Dependency-Track,
that both creates and reads VEX documents. Plus, I know of at least one other
tool today, Stack Aware, that reads
VEX documents. Moreover, I’ve been told there are a number of other tools, for
both creating and ingesting VEX documents, that will be available soon.
So, it seems that CISA’s second
recommendation was a good one. However, there’s one small problem in what they
recommended: They only mentioned the CSAF based VEX format. Since that format
is just a subset of the full CSAF format (and that subset still hasn’t been spelled
out, beyond a short
NTIA document that I prepared the first draft of in 2021, but which I now
realize isn’t complete), any tools to create or read CSAF VEX documents will
need to wait on tools that do the same for all CSAF documents – thus, what I just said about CSAF documents
in general applies directly to CSAF VEX documents as well.
However, there is another
VEX format. In January 2022, Steve Springett and Patrick Dwyer, co-leaders of
the OWASP CycloneDX (CDX) project, surprised everyone (including me, who had by
then become friends with Steve) by announcing
that CycloneDX v1.4 includes VEX capability. I can confirm that the CDX VEX
implementation is quite straightforward, so it doesn’t surprise me that there
are already tools both to read and write CycloneDX VEX documents.
So, CISA provided great advice in
their second recommendation: Software suppliers should create VEX documents in
CDX format, since there are currently tools both to create and read them. In
fact, the same applies to the first recommendation: The CycloneDX format can be
used to create Vulnerability
Disclosure Reports (VDR) just as easily as it can be used to create VEX
documents. As long as they’re not committed to CSAF and nothing else, a
supplier will be able to “Publish machine-readable security advisories” per
CISA’s recommendation.
Funny how these things work out…
Reminder: I'll be doing a podcast that will discuss VEX in depth on Wednesday, Nov. 30 at 10AM ET. I'll be able to discuss these issues in a lot more detail. Hope you can join me!
Any opinions expressed in this
blog post are strictly mine and are not necessarily shared by any of the
clients of Tom Alrich LLC. If you would
like to comment on what you have read here, I would love to hear from you.
Please email me at tom@tomalrich.com.
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