CVE-2017-14032 - certificate authentication bypass

[James Cowgill]

The following security bug was published for mbedtls:

[Vulnerability]
If a malicious peer supplies an X.509 certificate chain that has more
than MBEDTLS_X509_MAX_INTERMEDIATE_CA intermediates (which by default is
8), it could bypass authentication of the certificates, when the
authentication mode was set to 'optional' eg.
MBEDTLS_SSL_VERIFY_OPTIONAL. The issue could be triggered remotely by
both the client and server sides.

If the authentication mode, which can be set by the function
mbedtls_ssl_conf_authmode(), was set to 'required' eg.
MBEDTLS_SSL_VERIFY_REQUIRED which is the default, authentication would
occur normally as intended.

[Impact]
Depending on the platform, an attack exploiting this vulnerability could
allow successful impersonation of the intended peer and permit
man-in-the-middle attacks.

https://tls.mbed.org/tech-updates/security-advisories/mbedtls-security-advisory-2017-02

As far as I can tell, mbed TLS in xenial, zesty and artful are affected. No version of polarssl is affected.

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "mbedtls-2.2.1-2ubuntu0.2.debdiff" seems to be a debdiff. The ubuntu-sponsors team has been subscribed to the bug report so that they can review and hopefully sponsor the debdiff. If the attachment isn't a patch, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are member of the ~ubuntu-sponsors, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issue please contact him.]

[James Cowgill (jcowgill)]

The attached patches should fix this bug in xenial, zesty and artful. I have tested them using the certificate chain I used in the Debian bug report. The existing build tests / autopkgtests still pass.

[Simon Quigley (tsimonq2)]

Sponsoring to Artful (patch lgtm, thank you!) and unsubscribing ~ubuntu-sponsors. ~ubuntu-security-sponsors can take it from here.

Thank you for your contribution to Ubuntu!

[Launchpad Janitor (janitor)]

This bug was fixed in the package mbedtls - 2.5.1-1ubuntu1

---------------
mbedtls (2.5.1-1ubuntu1) artful; urgency=medium

  * SECURITY UPDATE: If optional authentication is configured, allows
    remote attackers to bypass peer authentication via an X.509 certificate
    chain with many intermediates. (LP: #1714640)
    - debian/patches/CVE-2017-14032.patch, backport two upstream patches to
      return and handle a new "fatal error" error code in case of long
      certificate chains.
    - CVE-2017-14032

 -- James Cowgill <email address hidden> Wed, 06 Sep 2017 21:11:46 -0500

[Tyler Hicks (tyhicks)]

These debdiffs look good to me. They're currently building in the ubuntu-security-proposed PPA and I'll be releasing them in xenial and zesty shortly. Thanks!

[Launchpad Janitor (janitor)]

This bug was fixed in the package mbedtls - 2.4.2-1ubuntu0.1

---------------
mbedtls (2.4.2-1ubuntu0.1) zesty-security; urgency=medium

  * SECURITY UPDATE: If optional authentication is configured, allows
    remote attackers to bypass peer authentication via an X.509 certificate
    chain with many intermediates. (LP: #1714640)
    - debian/patches/CVE-2017-14032.patch, backport two upstream patches to
      return and handle a new "fatal error" error code in case of long
      certificate chains.
    - CVE-2017-14032

 -- James Cowgill <email address hidden> Wed, 06 Sep 2017 21:03:02 +0100

[Launchpad Janitor (janitor)]

This bug was fixed in the package mbedtls - 2.2.1-2ubuntu0.2

---------------
mbedtls (2.2.1-2ubuntu0.2) xenial-security; urgency=medium

  * SECURITY UPDATE: If optional authentication is configured, allows
    remote attackers to bypass peer authentication via an X.509 certificate
    chain with many intermediates. (LP: #1714640)
    - debian/patches/CVE-2017-14032.patch, backport two upstream patches to
      return and handle a new "fatal error" error code in case of long
      certificate chains.
    - CVE-2017-14032

 -- James Cowgill <email address hidden> Wed, 06 Sep 2017 21:00:51 +0100