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What Is CVE-2025-27920?

In early 2025, a serious security issue was found in Output Messenger, specifically in versions before 2..63. The vulnerability (tracked as CVE-2025-27920) allows attackers to launch a directory traversal attack. This flaw happens when Output Messenger does not properly check user-supplied file paths, letting attackers sneak out of allowed folders and grab files from anywhere on the system.

Why Is This Dangerous?

Directory traversal (sometimes called "../" attack or path traversal) means an attacker can request files they shouldn't have access to—like configuration files, database details, or even secret keys. This could lead to leaked passwords, database access, or worse.

How Does the Attack Work?

When you upload or download files using Output Messenger, the system takes a file path as a parameter. But: in versions before 2..63, the input isn't filtered or sanitized well enough. Attackers can use ../ (dot-dot-slash) patterns to move up the folder tree—giving them access to private files outside the Messenger’s main data directory.

Suppose Output Messenger’s file download URL is

http://example.com/download?file=userdocs/report.txt

An attacker could modify this parameter to

http://example.com/download?file=../../../../windows/win.ini

Or, on Linux servers

http://example.com/download?file=../../../../etc/passwd

This sneaky ../../../../ part tells the server to go "up" directories before looking for the file. The result? The attacker gets files they shouldn’t be able to!

Here’s a very basic code sample of how this can go wrong

<?php
// BAD EXAMPLE (Vulnerable)
$file = $_GET['file'];
$base_dir = '/var/www/app/data/';
$path = $base_dir . $file;

if (file_exists($path)) {
    readfile($path);
} else {
    echo "File not found!";
}
?>

With no validation, attackers can break out of /var/www/app/data/ by using ../.

Proof-of-Concept (PoC) Exploit

If you want to test if your Output Messenger is vulnerable, try accessing a sensitive file with ../ sequences. For example:

curl "http://target-server/download?file=../../../../etc/hosts";

Or, replace with any file you want to sneak a peek at.

How To Fix and Protect Yourself

Output Messenger fixed this vulnerability in version 2..63.

Safe coding looks like this

<?php
// GOOD EXAMPLE (Safe)
$file = basename($_GET['file']); // strips path
$base_dir = '/var/www/app/data/';
$path = realpath($base_dir . $file);

if (strpos($path, realpath($base_dir)) !== ) {
    die("Access Denied!");
}
if (file_exists($path)) {
    readfile($path);
} else {
    echo "File not found!";
}
?>

References and Learn More

- Output Messenger Official Release Notes
- OWASP Directory Traversal Cheat Sheet
- CVE Details: CVE-2025-27920

Summary

CVE-2025-27920 is a real risk if you’re running Output Messenger below 2..63. Attackers can jump outside the intended folders and grab sensitive files with simple tricks. Protect your data and your users—update now, check your server logs, and always validate user input!

Have questions or need a hand? Drop a comment below. Stay safe!

Timeline

Published on: 05/05/2025 16:15:50 UTC
Last modified on: 05/21/2025 19:40:21 UTC