[gnutls-devel] DER decoding errors due to time format

Kurt Roeckx kurt at roeckx.be
Tue May 9 20:47:10 CEST 2017

On Tue, May 09, 2017 at 02:48:08PM +0200, Nikos Mavrogiannopoulos wrote:
> Hi,
>  gnutls 3.5.x is more strict in certificate decoding and performs
> various checks in the Time fields to ensure they are properly DER
> formatted. However, it is seems that this caused regressions with
> certain certificates generated by ovirt as seen in [0]. I am not sure
> which software was used to generate the problematic ones, however, it
> is most likely openssl, or some other open source software. Are you
> aware of other or similar decoding issues which were a result of 3.5.x
> being more strict in DER rules?
> The options we have are:
>  1. Ignore the error and insist on DER correctness in input certificates.
>  2. Allow incorrect formatted time fields in certificates
> unconditionally, e.g., with a special libtasn1 flag:
> https://gitlab.com/gnutls/libtasn1/commit/16bad0c72dcdfbe5512cdd6b46b251ab7484e5dc
> any other option I've missed? While I favor the first for its
> simplicity, reality has shown over the years we must yield towards the
> 'work' part.

NSS is strict in what it accepts. We've recently changed openssl to be
more strict too (commit 80770da39ebba0101079477611b7ce2f426653c5,
https://github.com/openssl/openssl/issues/2620), but maybe not
strict enough yet.

Anyway, as the github issue says, I could only find 35
certificates that chain to the mozilla root store that fail
the most strict check.


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