In May 2025, a major security flaw surfaced in popular forum software vBulletin. The issue, tracked as CVE-2025-48828, allows hackers to run arbitrary PHP code just by abusing how the template engine handles conditionals. Security researchers and attackers both found that by tweaking the way functions are called inside vBulletin templates, it’s possible to skip the usual protection and trigger ANY PHP code the attacker wants.

Let’s break down how this vulnerability works, see how it was exploited in the wild, and learn why the patch matters.

What Is vBulletin Template Syntax?

vBulletin lets admins customize forum pages using templates. These templates use a limited syntax for inserting logic or variables, just like mini-programs.

Normally, the template system should block dangerous code. It’s supposed to let you do things like

{if $user['isadmin']}
   Welcome, admin!
{/if}

But template conditionals can sometimes accept PHP function calls. Ideally, these are filtered or greatly restricted.

In PHP, you can call a function like this

var_dump("test");

But PHP also supports a tricky alternative

"var_dump"("test");

If you pass a string holding the function’s name, PHP will execute that function!

Turns out, *some vBulletin versions* ONLY checked direct function calls (like var_dump("test");). They didn't block the string-based version!

Attackers quickly figured out they could inject a payload like

{if "var_dump"("Hello from Hacker!")}
   This triggers code execution!
{/if}

Which, when parsed, actually runs var_dump("Hello from Hacker!") on the server—proving remote code execution.

Worse, with a little creativity, more dangerous functions (system, eval, etc.) could be called if they’re not blocked.

How Attackers Used This (May 2025)

In May, reports appeared ([see references](#references)) of attackers breaking into forums by posting template code containing these sneaky function calls. Some used it to dump environmental variables, expose database credentials, or drop web shells.

Suppose the attacker could edit templates (like via a plugin or a vulnerable admin panel)

{if "system"("id")}
    Code executed!
{/if}

Proof of Concept

Below is a simple PoC of what an attacker might do if they controlled templates and the patch isn't applied:

// Example: inside a template
{if "phpinfo"()}
   Info shown!
{/if}

What happens?: The PHP function phpinfo() is called, dumping server details to the page.

Another example to drop a webshell (not shown here for obvious reasons) could be launched with functions like file_put_contents.

Why Wasn’t This Blocked?

The template engine was checking for banned function names but not spotting the alternative syntax. Filtering "eval"("...") needed a different kind of string pattern match, which old versions didn’t do.

Patch Reference

- vBulletin Security Advisory – CVE-2025-48828
- GitHub Commit Showing the Fix

Admins: Upgrade immediately. If you can't, disable template editing, and audit all custom templates for weird function calls.

References

- Original Exploit Writeup by SecurityLab
- Patch Release Notes - vBulletin Forums
- CVE-2025-48828 on NVD
- PHP Docs: Variable functions

Conclusion

CVE-2025-48828 is a classic case where understanding obscure side-effects of a language can open up severe holes in software that millions rely on. If you run vBulletin, patch right now, audit templates, and watch for any similar issues in other template engines you use. As always, the simplest-sounding language "tricks" can have the biggest security impacts.

Timeline

Published on: 05/27/2025 04:15:45 UTC
Last modified on: 05/28/2025 15:01:30 UTC