CVE-2026-21875: ClipBucket Blind SQL Injection Vulnerability

CVE-2026-21875 Overview

ClipBucket v5 is an open source video sharing platform affected by a critical Blind SQL Injection vulnerability. Versions 5.5.2-#187 and below allow an attacker to perform Blind SQL Injection through the add comment section within a channel. When adding a comment within a channel, there is a POST request to the /actions/ajax.php endpoint. The obj_id parameter within the POST request is then used within the user_exists function of the upload/includes/classes/user.class.php file as the $id parameter. It is then used within the count function of the upload/includes/classes/db.class.php file. The $id parameter is concatenated into the query without validation or sanitization, allowing attackers to inject malicious SQL code.

Critical Impact

This SQL Injection vulnerability allows unauthenticated remote attackers to extract sensitive database information, modify data, or potentially gain complete control of the underlying database server. No patch is currently available.

Affected Products

• ClipBucket v5 versions 5.5.2-#187 and below

Discovery Timeline

• 2026-01-08 - CVE-2026-21875 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2026-21875

Vulnerability Analysis

This vulnerability represents a classic example of Blind SQL Injection (CWE-89) where user-supplied input is directly concatenated into a database query without proper validation or sanitization. The attack surface exists in the channel comment functionality, which is typically accessible to authenticated users of the platform.

The vulnerable code path begins when a user submits a comment on a channel page. The application sends a POST request to /actions/ajax.php containing the obj_id parameter. This parameter is passed through the user_exists function in user.class.php and ultimately reaches the count function in db.class.php, where it is directly incorporated into a SQL query.

Since the injection is blind, attackers cannot directly see the query results. However, they can infer information by observing application behavior differences (boolean-based blind injection) or by measuring response times (time-based blind injection). Using payloads like 1' or 1=1-- -, an attacker can manipulate the query logic to extract data character by character.

Root Cause

The root cause of this vulnerability is the direct concatenation of user-supplied input into SQL queries without implementing prepared statements or parameterized queries. The $id parameter received from user input flows through multiple class files without any input validation, sanitization, or escaping before being used in the database query. This violates secure coding principles and allows attackers to break out of the intended query context and inject arbitrary SQL commands.

Attack Vector

The attack is network-accessible and requires no user interaction or special privileges beyond potentially being an authenticated user of the platform. An attacker can exploit this vulnerability by:

1. Navigating to a channel page on the vulnerable ClipBucket instance
2. Using the comment functionality to submit a specially crafted payload
3. Injecting malicious SQL through the obj_id parameter in the POST request to /actions/ajax.php
4. Using boolean-based or time-based inference techniques to extract database contents

A payload such as 1' or 1=1-- - can be used to trigger the injection and verify the vulnerability exists. More sophisticated payloads can then be used to enumerate database structure and extract sensitive data including user credentials, session tokens, and other confidential information stored in the database.

Detection Methods for CVE-2026-21875

Indicators of Compromise

• Unusual or malformed POST requests to /actions/ajax.php containing SQL syntax characters
• Requests with obj_id parameters containing single quotes, double dashes, or SQL keywords like UNION, SELECT, or SLEEP
• Abnormal database query patterns or errors in application logs
• Increased database load or unusual response time patterns indicating time-based SQL injection attempts

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect SQL injection patterns in POST parameters
• Monitor application logs for requests containing SQL metacharacters such as single quotes, semicolons, and comment sequences
• Deploy database activity monitoring to detect anomalous query patterns or unauthorized data access
• Use intrusion detection systems with signatures for common SQL injection attack patterns

Monitoring Recommendations

• Enable detailed logging for all requests to /actions/ajax.php and review for suspicious patterns
• Set up alerts for database query errors that may indicate injection attempts
• Monitor for unusual data exfiltration patterns from the database server
• Track failed and successful authentication attempts that may indicate credential theft via SQL injection

How to Mitigate CVE-2026-21875

Immediate Actions Required

• Consider taking vulnerable ClipBucket instances offline until a patch is available
• Implement a Web Application Firewall (WAF) with SQL injection protection rules
• Restrict network access to the ClipBucket application to trusted IP ranges where possible
• Review database permissions and ensure the application uses a least-privilege database account
• Back up database contents and enable database audit logging

Patch Information

This issue does not have a fix at the time of publication. Organizations should monitor the GitHub Security Advisory for updates on patch availability. Until an official patch is released, implementing the workarounds below is strongly recommended.

Workarounds

• Deploy a Web Application Firewall (WAF) configured to block SQL injection attempts targeting the /actions/ajax.php endpoint
• Disable or restrict access to the channel comment functionality if not business-critical
• Implement input validation at the application layer to reject requests containing SQL metacharacters in the obj_id parameter
• Consider implementing prepared statements manually in the affected code files if you have development resources

# Example WAF rule for ModSecurity to block SQL injection in obj_id parameter
SecRule ARGS:obj_id "@rx (?i)(\b(and|or)\b.+?(>|<|=|!)|union.+?select|select.+?from|insert.+?into|update.+?set|delete.+?from|drop.+?table|truncate.+?table|exec.+?master\.\.xp_|sleep\s*\()" \
    "id:1001,phase:2,deny,status:403,log,msg:'SQL Injection attempt detected in obj_id parameter'"