CVE-2026-77939 in Flextype
Summary
by MITRE • 08/28/2026
Flextype CMS through v1.0.0-dev contains an expression language injection vulnerability that allows authenticated attackers with a valid API token to read arbitrary files by passing unsanitized user-supplied input to the Symfony ExpressionLanguage engine via the POST /api/v1/query endpoint. Attackers can leverage exposed application objects including filesystem() and serializers() within the evaluation scope to read arbitrary server files and achieve conditional remote code execution if a PHP file can be placed on disk through a secondary vector.
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Analysis
by VulDB Data Team • 08/28/2026
The vulnerability identified in Flextype CMS versions up to 1.0.0-dev represents a critical security flaw rooted in improper neutralization of special elements used in an expression language, commonly categorized under CWE-94 as Improper Control of Generation of Code or Script. This specific implementation weakness allows authenticated attackers who possess valid API tokens to inject malicious expressions into the Symfony ExpressionLanguage engine. The attack vector is facilitated through the POST /api/v1/query endpoint, where user-supplied input is passed directly for evaluation without adequate sanitization or validation mechanisms in place.
The technical core of this vulnerability lies in the exposure of powerful application objects within the expression language's evaluation scope. Specifically, functions such as filesystem() and serializers() are accessible to the injected expressions. This access grants the attacker the ability to interact with the underlying server infrastructure directly through the CMS interface. By leveraging these exposed services, an authenticated user can construct payloads that traverse the file system hierarchy, effectively bypassing standard application-level restrictions on data access.
The operational impact of this vulnerability is severe, primarily manifesting as unauthorized arbitrary file read capabilities. Attackers can exploit this flaw to extract sensitive configuration files, source code containing hardcoded credentials, database connection strings, or other proprietary information stored on the server. This level of access compromises the confidentiality and integrity of the entire system environment managed by Flextype CMS.
Furthermore, while the primary impact is data exfiltration via file reading, there exists a secondary vector that elevates this vulnerability to remote code execution under specific conditions. If an attacker can leverage other vulnerabilities or misconfigurations within the same application to upload a PHP script to a location accessible by the web server, they can utilize the expression language injection to trigger its execution. This conditional path transforms a data breach into full system compromise, allowing for complete control over the affected host.
From a threat intelligence perspective, this vulnerability aligns with ATT&CK techniques related to Command and Scripting Interpreter abuse as well as Data from Local System Retrieval. The reliance on authenticated access means that the attack surface is limited to users who have already obtained valid credentials or API tokens, which may involve credential theft via phishing or other initial access vectors prior to exploitation of this specific flaw.
Mitigation strategies must focus on immediate remediation and defensive hardening. The most effective solution is to upgrade Flextype CMS to a version where the Symfony ExpressionLanguage engine has been patched to restrict access to dangerous functions like filesystem() and serializers(). In cases where upgrading is not immediately feasible, administrators should implement strict input validation at the API gateway level to filter out expression language syntax characters such as parentheses, dots, and function names. Additionally, enforcing principle of least privilege for API tokens can limit the potential impact if a token is compromised by ensuring that only necessary endpoints are accessible with those credentials. Regular security audits and static code analysis should be employed to detect similar patterns in custom modules or extensions integrated into the CMS environment.