question about gsi -ca:verifyss option

[rptaylor]

Hello,

https://xrootd.slac.stanford.edu/doc/dev56/sec_config.htm#_Toc119617433

describes the -ca option:

verifyss     verify if self-signed, issuing a warning if not;

Default is verifyss. 

I can understand only verifying self-signed certificates as those would be the trust anchor roots which are distributed in /etc/grid-security/certificates, but if the result of verification failure is only a warning, it seems that verifyss as the default option is insecure. Does this mean that any certificate issued by any unverified self-signed certificate would be accepted with only a warning?

[amadio]

You may want to have a look at #2150, in particular this comment.

[bbockelm]

Does this mean that any certificate issued by any unverified self-signed certificate would be accepted with only a warning?

The documentation is misleading. It says:

Defines the CA verification level.

It really should say "define the trusted root CA verification level".

That is, if you have a fully verified chain, leading to a root CA found in the CA trust store (e.g., CA file or /etc/grid-security/certificates), do you check the signature on the trusted root CA itself?

Validating the trusted root CA makes little sense to me: if an attacker is competent enough to modify your CA store, they're probably competent enough to correctly self-sign their malicious CA.

At best, it's a waste of CPU cycles. At worst, since root CAs still are permitted to be SHA-1 self-signed, it causes a failure as in #2150.

[abh3]

Hi Brian,

OK, I agree. Could you come up withe the appropriate verbiage to substitute for the existing text and the change will happen.

Andy

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Does this mean that any certificate issued by any unverified self-signed certificate would be accepted with only a warning?

The documentation is misleading. It says:

Defines the CA verification level.

It really should say "define the trusted root CA verification level".

That is, if you have a fully verified chain, leading to a root CA found in the CA trust store (e.g., CA file or /etc/grid-security/certificates), do you check the signature on the trusted root CA itself?

Validating the trusted root CA makes little sense to me: if an attacker is competent enough to modify your CA store, they're probably competent enough to correctly self-sign their malicious CA.

At best, it's a waste of CPU cycles. At worst, since root CAs still are permitted to be SHA-1 self-signed, it causes a failure as in #2150https://github.com/xrootd/xrootd/issues/2150.

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[bbockelm]

How about replacing this:

Defines the CA verification level: noverify do not verify; verifyss verify if self-signed, issuing a warning if not; verify always verify the CA in the chain, failing when not possible. Default is verifyss.

with

Defines the trusted root CA self-signature verification level. The trusted root CAs are those installed in the CA file or directory. Options are: noverify do not verify the self-signature; this is the default behavior in OpenSSL; verifyss verify the self-signature, issuing a warning if verification fails; verify verify the self-signature, failing authentication when the verification fails. Default is verifyss.

[abh3]

Looks good to me, I'll make the documentation change. Thanks Brian.

[rptaylor]

I see, thanks for clarifying what the verification is referring to.

[abh3]

Documentation has been updated.