CVE-2026-53756: Emlog CMS Pro Blind SQL Injection Vulnerability

CVE-2026-53756 Overview

Emlog is an open source website building system. Versions of Emlog CMS Pro prior to 2.6.16 contain a blind SQL injection vulnerability in the User_Model::getUserDataByLogin() function. The $account parameter is interpolated directly into SQL queries without any filtering or parameterization. The injection point is reachable through the authentication cookie validation path, where the $username value is extracted from the cookie and passed unfiltered into the SQL query. The vulnerable code path is guarded only by an HMAC signature that requires knowledge of AUTH_KEY to forge, limiting exploitation to actors who already possess elevated privileges. The issue has been patched in version 2.6.16.

Critical Impact
Attackers with knowledge of AUTH_KEY can craft forged authentication cookies containing SQL payloads, enabling blind extraction of arbitrary database content including user credentials.

Affected Products

Emlog CMS Pro versions prior to 2.6.16
Component: include/model/user_model.php (User_Model::getUserDataByLogin())
Authentication path: cookie validation flow

Discovery Timeline

2026-09-04 - CVE-2026-53756 published to NVD
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-53756

Vulnerability Analysis

The vulnerability is a classic SQL injection [CWE-89] in the login lookup routine of Emlog Pro. When a user presents an authentication cookie, the application extracts the $username field and forwards it to getUserDataByLogin($account). That function concatenates the value into a raw SQL statement without escaping or binding parameters. Because no result is returned to the response body on this path, exploitation relies on blind techniques such as boolean-based or time-based inference. The HMAC signature check on the cookie constrains exploitation to actors who can forge valid cookies, which requires the server-side AUTH_KEY secret.

Root Cause

The root cause is unsafe string interpolation of user-controlled input into a dynamic SQL query. The original implementation of getUserDataByLogin() built the query using the raw $account variable in a double-quoted string. No call to escape_string() or prepared statement API preceded query execution, violating standard input sanitization requirements for database access layers.

Attack Vector

The attack requires network access to the Emlog application and knowledge of the AUTH_KEY value used to sign authentication cookies. Given that key, an attacker forges a cookie whose $username component contains a SQL payload. When the cookie validation path invokes getUserDataByLogin(), the payload executes inside the SELECT query against the user table. Response timing or conditional behavior can be used to infer the contents of arbitrary rows and columns.

php

         return $row;
     }
 
+    /**
+     * 根据用户名或邮箱获取用户信息
+     */
     public function getUserDataByLogin($account)
     {
         if (empty($account)) {
             return false;
         }
+        $account = $this->db->escape_string($account);
         $ret = $this->db->once_fetch_array("SELECT * FROM " . DB_PREFIX . "user WHERE username = '$account'");
         if (!$ret) {
             $ret = $this->db->once_fetch_array("SELECT * FROM " . DB_PREFIX . "user WHERE email = '$account'");

Source: GitHub Commit 92b6eea. The patch introduces a call to $this->db->escape_string($account) before the value is interpolated into either the username or email lookup query.

Detection Methods for CVE-2026-53756

Indicators of Compromise

Authentication cookies containing SQL metacharacters such as single quotes, UNION, SLEEP(, or BENCHMARK( in the $username field.
Database query logs showing malformed SELECT * FROM <prefix>user WHERE username = '...' statements with injected clauses.
Repeated authentication requests with consistent HMAC signatures but varying $username payloads, indicative of blind inference loops.
Unusual outbound query latency correlating with time-based blind SQLi payloads.

Detection Strategies

Enable MySQL general query logging temporarily and grep for anomalous patterns against the emlog_user table.
Deploy a web application firewall rule that inspects decoded cookie values for SQL syntax before requests reach the application.
Alert on any cookie payload where the decoded $username field exceeds normal length or contains SQL keywords.
Correlate authentication requests with response time deltas to identify time-based blind injection attempts.

Monitoring Recommendations

Monitor application error logs for database driver exceptions originating from user_model.php.
Track failed login rates from single source IPs to detect enumeration attempts leveraging the injection.
Audit access to the AUTH_KEY configuration value and rotate it if any exposure is suspected.

How to Mitigate CVE-2026-53756

Immediate Actions Required

Upgrade Emlog Pro to version 2.6.16 or later, which applies the escape_string() sanitization fix.
Rotate the AUTH_KEY value in the Emlog configuration to invalidate any previously forged authentication cookies.
Force logout of all active sessions and require users to re-authenticate after the upgrade.
Review database logs and user table contents for signs of unauthorized queries or data extraction.

Patch Information

The fix is available in the Emlog Pro 2.6.16 release. The specific code change is documented in GitHub commit 92b6eea and the coordinated disclosure is tracked in GHSA-xq97-53c2-vvfg.

Workarounds

Restrict access to the Emlog administrative interface using network-layer controls until the patch can be applied.
Deploy a WAF signature that blocks requests whose decoded authentication cookie contains SQL metacharacters.
Ensure the AUTH_KEY value has never been committed to source control, backup archives, or shared configuration stores.

bash

# Verify installed Emlog Pro version and upgrade path
grep -R "Version" /var/www/emlog/include/lib/version.php

# Rotate AUTH_KEY after upgrade (example: generate 64-char random key)
php -r "echo bin2hex(random_bytes(32)) . PHP_EOL;"

# Update config/config.php with the new AUTH_KEY value, then restart PHP-FPM
sudo systemctl restart php-fpm