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GHSA-gq27-fc8w-vcmp
No affected components available
Summary
An unauthenticated attacker can execute arbitrary JavaScript in any Admidio user's browser through a reflected XSS in system/msg_window.php. The endpoint passes user input through htmlspecialchars(), which does not encode square brackets. A subsequent call to Language::prepareTextPlaceholders() converts those brackets into HTML angle brackets, producing executable markup.
Details
The msg_window.php endpoint accepts message_id and message_var1 as GET parameters. At line 146, the code passes message_var1 through htmlspecialchars() before inserting it into the language string as a placeholder:
// system/msg_window.php:146
$messageText = $gL10n->get($messageId, array(htmlspecialchars($messageVar1)));
htmlspecialchars() encodes <, >, &, ", and ' but leaves [ and ] untouched. The Language::get() method calls Language::prepareTextPlaceholders(), which performs a character-level translation:
// src/Infrastructure/Language.php:497
$text = strtr($text, '[]', '<>');
This converts all square brackets in the output string, including those from user input, into angle brackets. An attacker submits [script]alert(document.domain)[/script], which survives htmlspecialchars() unchanged, then becomes <script>alert(document.domain)</script> after placeholder preparation.
The application sets no Content-Security-Policy headers, so inline scripts execute without restriction.
Proof of Concept
Visit the following URL on any Admidio installation (no authentication required):
https://<admidio-host>/system/msg_window.php?message_id=INS_INSTALLATION_VERSION&message_var1=%5Bscript%5Dalert(document.domain)%5B/script%5D
The server responds with an HTML page containing:
Installation version <script>alert(document.domain)</script>
The JavaScript executes in the context of the Admidio origin, displaying the current domain in an alert dialog.
Impact
An attacker crafts a malicious URL and sends it to any Admidio user. When the victim clicks the link, attacker-controlled JavaScript runs in their browser session. The attacker can steal session cookies, perform administrative operations on behalf of the victim, or redirect the victim to phishing pages. The endpoint requires no authentication.
Recommended Fix
Apply output encoding after Language::prepareTextPlaceholders() runs, or stop translating square brackets that originate from user-supplied placeholder values. A targeted fix: escape [ and ] in user input before passing it into Language::get().
Found by aisafe.io
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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