CVE-2026-59989 in Phalcon
Summary
by MITRE • 08/21/2026
Phalcon is a high-performance, full-stack PHP framework. In 5.15.0 and earlier, resolveFilter in phalcon/Mvc/View/Engine/Volt/Compiler.zep builds the join filter by inserting the raw separator and array token values into generated PHP without passing them through expression(). An attacker who can influence Volt template source can place quote-breaking content in a join argument, inject PHP into the compiled cache file, and execute it when Phalcon\Mvc\View\Engine\Volt::render() loads the template. This issue is fixed in version 5.16.0.
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Analysis
by VulDB Data Team • 08/21/2026
The vulnerability identified in Phalcon versions prior to 5.16.0 represents a critical server-side code injection flaw within the Volt templating engine, specifically located in the resolveFilter function of the Mvc/View/Engine/Volt/Compiler component. As a high-performance full-stack PHP framework, Phacon relies on its template engines to generate dynamic web content efficiently. The core technical deficiency arises from improper input validation and sanitization during the compilation phase of Volt templates. When processing join filters, which are used to concatenate array elements into strings using a specified separator, the compiler directly inserts raw user-supplied values for both the separator and the array tokens into the generated PHP code cache files without passing them through the necessary expression() function or other escaping mechanisms designed to neutralize malicious payloads.
This architectural oversight allows an attacker who possesses the ability to influence the source of Volt templates to inject arbitrary PHP code directly into the compiled cache file. By crafting a join argument that includes quote-breaking content, such as unescaped double quotes followed by closing tags and new PHP statements, the attacker can break out of the intended string context within the generated PHP syntax. Once this malicious payload is embedded in the cache file, it remains dormant until the Phalcon MVC view engine attempts to render the template via the Volt::render() method. At that point, the web server interprets the injected code as valid PHP instructions, leading to immediate execution with the privileges of the web application process.
The operational impact of this vulnerability is severe, effectively resulting in remote code execution (RCE) on the target system. An attacker can leverage this flaw to execute arbitrary commands, exfiltrate sensitive data from the database or file system, modify application logic, or establish persistent backdoors within the server environment. Because the vulnerability resides in a core templating component used for rendering views, it is particularly dangerous as it may be triggered by any user input that flows into template variables involved in join operations. The persistence of the malicious code in the cache files means that even if the initial request vector is mitigated or patched at the application logic level, previously cached templates containing the injected payload will continue to execute until the cache is explicitly cleared or expires.
To mitigate this vulnerability, organizations must immediately upgrade Phalcon to version 5.16.0 or later, where the issue has been resolved by ensuring that all inputs passed to join filters are properly sanitized and escaped before being inserted into the generated PHP code. In environments where an immediate upgrade is not feasible, administrators should implement strict input validation on any user-supplied data that is used within Volt templates, particularly in arguments for filter functions like join. Additionally, disabling or restricting access to template editing capabilities if they are exposed to end-users can significantly reduce the attack surface. Regularly clearing the view cache after deployment updates ensures that no stale or potentially compromised compiled templates remain active on the server. This incident highlights the importance of rigorous input handling in templating engines and aligns with CWE-94, which describes Improper Control of Generation of Code (Code Injection), as well as MITRE ATT&CK techniques related to Server-Side Request Forgery and Command Execution via web application vulnerabilities.