CVE-2026-25923 in mylittleforum
Summary
by MITRE • 02/10/2026
my little forum is a PHP and MySQL based internet forum that displays the messages in classical threaded view. Prior to 20260208.1, the application fails to filter the phar:// protocol in URL validation, allowing attackers to upload a malicious Phar Polyglot file (disguised as JPEG) via the image upload feature, trigger Phar deserialization through BBCode [img] tag processing, and exploit Smarty 4.1.0 POP chain to achieve arbitrary file deletion. This vulnerability is fixed in 20260208.1.
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Analysis
by VulDB Data Team • 03/17/2026
The vulnerability identified as CVE-2026-25923 affects my little forum, a PHP and MySQL based internet forum application that utilizes classical threaded message display. This security flaw exists in versions prior to 20260208.1 and represents a critical path to arbitrary file deletion through a sophisticated attack chain. The vulnerability stems from insufficient input validation within the application's URL handling mechanisms, specifically failing to properly filter the phar:// protocol during URL validation processes.
The technical exploitation begins with an attacker leveraging the image upload feature to upload a malicious Phar Polyglot file that appears as a legitimate JPEG image to end users. This file serves as a deceptive payload that bypasses initial security checks due to the application's inadequate protocol filtering. The malicious file triggers Phar deserialization when processed through the BBCode [img] tag functionality, which represents a common attack vector in web applications where user-supplied content is parsed and executed. The vulnerability specifically exploits the Smarty 4.1.0 PHP template engine's Property Overriding and POP (Point of No Return) chain, which allows attackers to manipulate object states and execute arbitrary code. The POP chain leverages the template engine's object serialization mechanism to achieve arbitrary file deletion through carefully crafted object manipulation.
This vulnerability demonstrates a classic case of insufficient input validation and improper protocol handling that directly relates to CWE-20, which covers improper input validation, and CWE-77, which addresses command and control injection flaws. The attack scenario aligns with ATT&CK techniques such as T1059.007 for PHP and T1566.001 for malicious file execution through web applications. The operational impact is severe as it allows attackers to delete arbitrary files on the server, potentially compromising the entire application infrastructure and leading to complete system compromise. The vulnerability's exploitation requires user interaction through the BBCode image tag processing, making it particularly dangerous in collaborative environments where users can submit content. The fix implemented in version 20260208.1 addresses the core issue by properly filtering the phar:// protocol in URL validation and strengthening the input sanitization processes. Organizations should immediately upgrade to the patched version and implement additional monitoring for suspicious file uploads and image processing activities. The vulnerability highlights the importance of comprehensive protocol filtering and the need for robust input validation in web applications, particularly those that process user-supplied content through template engines. Security teams should also consider implementing web application firewalls and additional file type validation measures to prevent similar vulnerabilities in other components of their infrastructure.