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Message-ID: <e24f1ae1-32d5-4ed4-ba82-19f11cdf460f@rub.de>
Date: Thu, 26 Sep 2024 13:24:53 +0200
From: Fabian Bäumer <fabian.baeumer@....de>
To: oss-security@...ts.openwall.com
Subject: Re: CVE-2024-40761: Apache Answer: Avatar URL leaked
user email addresses
> Using the MD5 value of a user's email to access Gravatar is insecure and can lead to the leakage of user email.
Yes, but only through brute-force. The one-way property of MD5 is still
unbroken.
> The official recommendation is to use SHA256 instead.
This doesn't change a thing. You may as well brute-force SHA256 thus the
information leakage remains the same.
I'd recommend to switch to using HMAC (with SHA256 for good measure) as
a keyed pseudo-random function here. When the secret ist kept - well -
secret, negligible information about the user's email address is leaked.
Performing brute-force without knowledge of the secret key is also not
tractable.
Side note: This change does take away Gravatar's global property (i.e.
across multiple sites). I can't think of a straightforward way to
achieve global avatars without leaking any information about the user.
However, if the goal here is to have a simple avatar picture this should
be fine.
M. Sc. Fabian Bäumer
Chair for Network and Data Security
Ruhr University Bochum
Universitätsstr. 150, Building MC 4/145
44780 Bochum
Germany
Am 25.09.24 um 08:28 schrieb Enxin Xie:
> Severity: low
>
> Affected versions:
>
> - Apache Answer through 1.3.5
>
> Description:
>
> Inadequate Encryption Strength vulnerability in Apache Answer.
>
> This issue affects Apache Answer: through 1.3.5.
>
> 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.
> Users are recommended to upgrade to version 1.4.0, which fixes the issue.
>
> Credit:
>
> 张岳熙 (reporter)
>
> References:
>
> https://answer.incubator.apache.org
> https://www.cve.org/CVERecord?id=CVE-2024-40761
>
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