On Wednesday, March 11, 2020 12:20:38 PM EDT Reese, Brian J CTR (USA) wrote:
> Having the CBC mode ciphers enabled will trigger Nessus Plugin ID 70658:
>
> https://www.tenable.com/plugins/nessus/70658
>
> This was likely a factor in DISA's decision to remove them from the STIG.
> Older versions of the STIG (at least the RHEL 6 STIG) had the CBC modes
> enabled, but they were taken out at some point for reasons unrelated to
> FIPS 140-2.
Right. There was a vulnerability on RHEL 5 & 6 that was fixed. This is
CVE-2008-5161. Fixed long ago.
-Steve
> On Wed, Mar 11, 2020, at 11:36 AM, Matěj Týč wrote:
> > One of RHEL7 bugzillas [1] shows an interesting discrepancy between our
> >
> > content and STIG:
> > * We feature [2] a rule "Use Only FIPS 140-2 Validated Ciphers"
> > * STIG has its own [3] "A FIPS 140-2 approved cryptographic algorithm
> >
> > must be used for SSH communications."
> > There is a discrepancy between the two - while we claim that the
> > following ciphers are FIPS 140-2 certified on Red Hat Enterprise Linux
> >
> > 7, only three of them are recognized as such by the STIG:
> > * aes128-ctr(STIG)
> > * aes192-ctr(STIG)
> > * aes256-ctr(STIG)
> > * aes128-cb
> > * aes192-cbc
> > * aes256-cbc
> > * 3des-cbc
> > * rijndael-cbc@lysator.liu.se
> >
> > I have confirmed correctness of our description with our FIPS SME Tomas
> > Mraz (in CC), so this issue looks as a bug in STIG - either the
> > requirement is too strict, so it is incorrect, or it is supposed to be
> > strict, and it should therefore be reworded, and we need to create a
> > new rule in our content.
>
> Indeed, the STIG allows fewer ciphers than FIPS allows; the STIG currently
> says "If any ciphers other than "aes128-ctr", "aes192-ctr", or
> "aes256-ctr" are listed, the "Ciphers" keyword is missing, or the returned
> line is commented out, this is a finding." [4]
>
> Similarly, for the MACs allowed, "If any ciphers other than "hmac-sha2-256"
> or "hmac-sha2-512" are listed or the returned line is commented out, this
> is a finding." [5]
>
> More are permitted by FIPS than by SSH, but the STIG is FIPS compliant
> as-is, using a subset of the FIPS ciphers. From the Security Policy
> document for the certification [6],
>
> Only the following ciphers are allowed:
> - aes128-ctr
> - aes192-ctr
> - aes256-ctr
> - aes128-cbc
> - aes192-cbc
> - aes256-cbc
> - 3des-cbc
> - rijndael-cbc@lysator.liu.se
> Only the following message authentication codes are allowed:
> - hmac-sha1
> - hmac-sha2-256
> - hmac-sha2-512
> - hmac-sha1-etm@openssh.com
> - hmac-sha2-256-etm@openssh.com
> - hmac-sha2-512-etm@openssh.com
>
> > What is the procedure in cases like this?
>
> I'd just configure the STIG subset of FIPS, and maybe ask DISA to add a
> clarification note to the STIG. Many folks are concerned about the
> FIPS-permitted 3DES algorithm [7], "3DES is deprecated for all new
> applications and usage is disallowed after 2023"
>
>
> V/r,
> James Cassell
>
>
> [4]
> Caution-https://vaulted.io/library/disa-stigs-srgs/red_hat_enterprise_linu
> x_7_security_technical_implementation_guide/V-72221?version=V2R6
>
> [5]
> Caution-https://vaulted.io/library/disa-stigs-srgs/red_hat_enterprise_linu
> x_7_security_technical_implementation_guide/V-72253?version=V2R6
>
> [6]
> Caution-https://csrc.nist.gov/CSRC/media/projects/cryptographic-module-val
> idation-program/documents/security-policies/140sp3067.pdf
>
> [7]
> Caution-https://www.cryptomathic.com/news-events/blog/3des-is-officially-b
> eing-retired
> > References:
> > > [1]: Caution-https://bugzilla.redhat.com/show_bug.cgi?id=1781244
> > >
> > > [2]:
> > > Caution-https://static.open-scap.org/ssg-guides/ssg-rhel7-guide-stig.
> > > html#xccdf_org.ssgproject.content_rule_sshd_use_approved_ciphers>
> > > [3]:
> > Caution-https://www.stigviewer.com/stig/red_hat_enterprise_linux_7/2017-1
> > 2-14/finding/V-72221
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