CVE-2025-47784: Emlog Deserialization Vulnerability

CVE-2025-47784 Overview

CVE-2025-47784 is an insecure deserialization vulnerability affecting Emlog, an open source website building system. Versions 2.5.13 and prior contain a flaw where a user can create a carefully crafted nickname that causes str_replace to replace the value of name_orig with an empty string, resulting in deserialization failure and returning false. This vulnerability could allow attackers to manipulate the deserialization process through network-based attacks without requiring authentication.

Critical Impact
Attackers can exploit the str_replace function behavior in the cache parsing mechanism to cause deserialization failures, potentially leading to integrity violations in the affected Emlog installations.

Affected Products

Emlog versions 2.5.13 and prior
Emlog Pro editions (all versions prior to the fix)
Emlog installations using the vulnerable cache.php implementation

Discovery Timeline

2025-05-15 - CVE-2025-47784 published to NVD
2025-10-20 - Last updated in NVD database

Technical Details for CVE-2025-47784

Vulnerability Analysis

This insecure deserialization vulnerability exists in the cache handling mechanism of Emlog. The root issue lies in how the application processes cached data using str_replace to strip a PHP exit header (<?php exit;//) before deserializing the content. An attacker who creates a nickname containing the exact string <?php exit;// can cause the str_replace function to match and replace unintended portions of the cached data, corrupting the serialized content and causing the unserialize function to fail.

The vulnerability is network-accessible and requires no authentication or user interaction to exploit. While the immediate impact is integrity-focused rather than achieving code execution, deserialization failures in PHP applications can have cascading effects on application stability and data integrity.

Root Cause

The vulnerability stems from the use of str_replace for stripping the PHP header prefix from cached data. The str_replace function performs global replacement of all occurrences of the search string, not just the prefix. This means if user-controlled data (such as a nickname) contains the string <?php exit;//, it will also be replaced with an empty string, corrupting the serialized data structure.

Attack Vector

The attack is network-based and can be executed by any user capable of setting a nickname within the Emlog system. The attacker crafts a nickname containing the exact header string <?php exit;//. When this nickname is serialized and cached, subsequent cache reads will:

Load the cache file contents
Apply str_replace to remove the header prefix
Inadvertently also remove the attacker's nickname content
Attempt to deserialize the now-corrupted data
Fail deserialization, returning false

php

// Vulnerable code in include/lib/cache.php
if ($cacheData = file_get_contents($cacheFile)) {
    clearstatcache();
-   $this->{$cacheProperty} = unserialize(str_replace("<?php exit;//", '', $cacheData));
+   $prefixLen = 13; // Length of "<?php exit;//"
+   $this->{$cacheProperty} = unserialize(substr($cacheData, $prefixLen));
    return $this->{$cacheProperty};
}

Source: GitHub Commit Details

Detection Methods for CVE-2025-47784

Indicators of Compromise

User accounts with nicknames containing <?php exit;// or similar PHP code patterns
Cache file corruption or deserialization errors in Emlog application logs
Unexpected false return values from cache retrieval operations
Application errors related to unserialize() function failures

Detection Strategies

Monitor application logs for PHP deserialization warnings or errors in include/lib/cache.php
Implement input validation rules to detect and flag nicknames containing PHP opening tags or exit statements
Review user database entries for suspicious patterns matching <?php or exit;
Deploy web application firewall (WAF) rules to detect PHP code injection patterns in form submissions

Monitoring Recommendations

Enable detailed error logging for the Emlog application to capture deserialization failures
Set up alerts for repeated cache-related errors that may indicate exploitation attempts
Monitor user registration and profile update activities for suspicious nickname patterns
Implement file integrity monitoring on cache directories to detect unexpected corruption

How to Mitigate CVE-2025-47784

Immediate Actions Required

Update Emlog to a version containing commit 9643250802188b791419e3c2188577073256a8a2 or later
Audit existing user accounts for nicknames containing suspicious patterns like <?php exit;//
Clear and regenerate all cache files after applying the patch
Review and sanitize any user-controlled data that may be serialized and cached

Patch Information

The vulnerability has been addressed in commit 9643250802188b791419e3c2188577073256a8a2. The fix replaces the vulnerable str_replace approach with substr, which only removes the fixed-length prefix (13 characters) rather than replacing all occurrences of the header string throughout the data. This ensures user-controlled content cannot interfere with the header stripping process.

For detailed patch information, see the GitHub Security Advisory and the GitHub Commit Details.

Workarounds

Implement server-side input validation to reject nicknames containing <?php, exit;, or similar PHP code patterns
Add a web application firewall rule to block requests containing PHP code in user input fields
Temporarily disable user self-registration or profile editing capabilities until the patch is applied
Implement content security policies that sanitize all user inputs before storage

bash

# Configuration example
# Apply the official patch by updating to the fixed version
cd /path/to/emlog
git fetch origin
git checkout 9643250802188b791419e3c2188577073256a8a2

# Clear cache files after patching
rm -rf content/cache/*

# Verify the fix is in place
grep -n "substr" include/lib/cache.php