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Date: Wed, 25 Jun 2014 19:07:27 -0400 (EDT)
Subject: Re: Question regarding CVE applicability of missing HttpOnly flag

Hash: SHA1

There admittedly isn't a precise distinction between "opportunity for
security improvement" (a CVE ID cannot be assigned) and "exposure" (a
CVE ID can be assigned in some cases).

In web applications that function correctly with the HTTPOnly flag for
a cookie, absence of this flag might be categorized as a CWE-668
("Exposure of Resource to Wrong Sphere") issue. In general, factors
that can be considered include:

  -- are there compatibility downsides to setting the flag? (An
     example of a downside might be: a popular but noncompliant
     browser completely ignores the cookie if the flag is set.)

     [ Obviously each CVE assignment is on a per-product basis, and
       there wouldn't be a CVE about HTTPOnly if a product's design
       relies on script access to a cookie. ]

  -- does the flag interfere with plausible use cases? (An example of
     a use case might be: script code that doesn't need to know the
     value of a cookie, but was designed to read the cookie anyway to
     assess whether an attack involving long cookie values is

  -- are there vendors who recommend against the flag?

  -- compared to the development cost in arranging for the flag to be
     set, is it possible that the real-life benefit is too small?

  -- are there other known or potential costs to setting the flag?
     (There might not be a good example here, e.g., there probably
     aren't bandwidth considerations where 9 or 10 more bytes is a
     deal breaker.)

If the answer to all of these questions is no, then it starts becoming
reasonable to argue that absence of the flag is an implementation

> like running SELinux (or AppArmor), running a virus scanner, and
> having a firewall

All of those seem to, in practice, have a relatively much greater
chance of introducing new vulnerabilities because of the required
implementation complexity.

- -- 
CVE assignment team, MITRE CVE Numbering Authority
M/S M300
202 Burlington Road, Bedford, MA 01730 USA
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