critical CVSS 9.8

CVE-2026-21875·PHP vulnerability

ClipBucket v5 is an open source video sharing platform. 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 to /actions/ajax.php 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, and a user-supplied input like 1' or 1=1-- - can be used to trigger the injection. This issue does not have a fix at the time of publication.

Severity
critical
Software
PHP
Fixed in
5.5.2-191
Published
2026-01-08

Affected versions

From: 5.3

Until: 5.5.2-191

Fixed in: 5.5.2-191

How to fix this CVE

ClipBucket v5 versions up to 5.5.2-#187 contain a critical blind SQL injection vulnerability in the comment functionality that allows unauthenticated attackers to extract sensitive database information. Update ClipBucket immediately to version 5.5.2-#191 or later, which patches the unsafe parameter handling in the ajax.php endpoint. Review your PHP application code to ensure all user inputs are parameterized using prepared statements before passing them to database queries.

sudo dnf update php

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST /actions/ajax.php.*obj_id=.*['\"]\s*(OR|AND|UNION|--|;|/\*)

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement a WAF rule to block POST requests to /actions/ajax.php where the obj_id parameter contains SQL metacharacters or common injection patterns. Specifically, deny requests matching: obj_id parameter contains single quotes, double quotes, SQL keywords (UNION, SELECT, OR, AND), SQL comments (-- or /*), or semicolons. Additionally, enforce strict input validation requiring obj_id to be numeric only.

How to check if you are affected

  1. Run `php -v` to confirm the installed PHP version and verify your ClipBucket installation version by checking the VERSION file in the ClipBucket root directory
  2. Verify the vulnerable /actions/ajax.php endpoint exists and check file permissions with `ls -la /path/to/clipbucket/actions/ajax.php`
  3. Search your web server logs (Apache/Nginx) for POST requests to /actions/ajax.php containing SQL metacharacters like single quotes, dashes, or 'or 1=1' patterns: `grep -i "ajax.php.*\('+\|or\s*1=1\)" /var/log/apache2/access.log`
  4. Confirm the patch by checking if ClipBucket version is 5.5.2-#191 or higher via `grep -i 'version' /path/to/clipbucket/VERSION` and verify that the user.class.php file uses parameterized queries in the user_exists function

FAQ

What is CVE-2026-21875?

CVE-2026-21875 is a critical blind SQL injection vulnerability in ClipBucket v5 that exists in the comment submission feature. An attacker can manipulate the obj_id parameter sent to /actions/ajax.php to execute arbitrary SQL queries without authentication, potentially exposing or modifying the entire database.

Is CVE-2026-21875 being actively exploited?

No, CVE-2026-21875 is not currently listed in the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits have been released as of this advisory.

What versions of PHP are affected by CVE-2026-21875?

ClipBucket v5 versions 5.3 through 5.5.2-#187 are vulnerable. The vulnerability was remediated in version 5.5.2-#191 and later.

How do I check if my server is vulnerable to CVE-2026-21875?

Determine your ClipBucket version by examining the VERSION file in your ClipBucket installation directory. If the version is 5.5.2-#187 or earlier, your instance is vulnerable. You can also test by sending a POST request with a malicious SQL payload to /actions/ajax.php with the obj_id parameter set to `1' or 1=1-- -` and observing if the application behavior changes unexpectedly.

Does Defensia detect CVE-2026-21875?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PHP is installed on a monitored server, CVE-2026-21875 will appear in your dashboard with remediation steps.

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References

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