Re: CVE-2024-40761: Apache Answer: Avatar URL leaked user email addresses

[LinkinStar <linkinstar () apache org>]

Hi Alexander,

First of all, thank you very much for your feedback.

Because *Gravatar recommends using sha-256*, we believe there must be a
reason for its modification. Since the official recommendation is to change
the encryption method, why not implement it according to the official
requirements? You must admit that sha-256 is more difficult than md5, even
if only slightly. Although this may not completely solve the problem, I
believe following the official recommendation would be marginally better,
wouldn't it? So I think this fix itself is acceptable.

Best regards,
LinkinStar

On Wed, Sep 25, 2024 at 11:21 PM Solar Designer <solar () openwall com> wrote:

> On Wed, Sep 25, 2024 at 06:28:16AM +0000, Enxin Xie wrote:
> > Using the MD5 value of a user's email to access Gravatar is insecure and
> can lead to the leakage of user email. The official recommendation is to
> use SHA256 instead.
>
> For practical purposes, this sounds like almost no change to me.  I've
> just checked and https://docs.gravatar.com/api/avatars/hash/ does say:
>
> > All URLs on Gravatar are based on the use of the hashed value of an
> > email address. Images and profiles are both accessed via the hash of an
> > email, and it is considered the primary way of identifying an identity
> > within the system. To ensure a consistent and accurate hash, the
> > following steps should be taken to create a hash:
> >
> > 1. Trim leading and trailing whitespace from an email address
> > 2. Force all characters to lower-case
> > 3. hash the final string with SHA256
>
> So Gravatar URLs by design allow for quick checking of email addresses
> against them, and thus allow to infer not-too-cryptic addresses.  Both
> MD5 and SHA-256 are very fast, with speeds in many billion per second
> per GPU, with SHA-256 being only a few times slower than MD5.  MD5's
> cryptographic weaknesses are irrelevant to this use case.
>
> So I think this CVE should either be rejected (as the issue is with
> Gravatar, not with implementations) or considered unfixable (within
> spec) and thus not fixed.
>
> Alexander