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Message-ID:
<BY3PR13MB4769D5EB969804CD5B905A748B692@BY3PR13MB4769.namprd13.prod.outlook.com>
Date: Wed, 25 Sep 2024 17:38:03 +0000
From: "Goldberg, Adam" <Adam.Goldberg@...y.com>
To: "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com>
Subject: RE: CVE-2024-40761: Apache Answer: Avatar URL leaked
user email addresses
> 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://urldefense.com/v3/__https://docs.gravatar.com/api/avatars/hash/__;!!JmoZiZGBv3RvKRSx!6zoU_J4wgUshOcGT7WCRwWgz0hjESorDYcuCX8cOARG6zrVpuLHmeayYJmf2ZnIO1QaQVFfeopQ2u6GQ6g$ 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
Note that this is a recommendation, "the following steps *should* ...", which doesn't require that those three steps be taken.
> 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.
See above, it seems to be an implementation issue (at least in part -- an application must take specific actions in order to create the hash in a secure way).
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