CVE-2026-94389 in SMTP Newsletter Plugin
Summary
by MITRE • 09/30/2026
Unauthenticated Remote Code Execution (RCE) in AcyMailing SMTP Newsletter <= 11.0.5 versions.
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified as an unauthenticated remote code execution flaw within AcyMailing SMTP Newsletter versions prior to or equal to 11.0.5 represents a critical security failure that allows attackers to execute arbitrary commands on the target server without requiring valid credentials. This specific weakness stems from insufficient input validation and sanitization mechanisms in the plugin's handling of user-supplied data, particularly within components related to SMTP configuration or newsletter management interfaces that are accessible via HTTP requests. The absence of proper authentication checks for certain endpoints creates a direct pathway for exploitation by any remote actor with network access to the vulnerable WordPress instance. This type of vulnerability is classified under CWE-94 as Improper Control of Generation of Code, often referred to colloquially as code injection, where the application fails to neutralize special elements that could be interpreted as executable commands by the underlying system or scripting engine.
From an operational perspective, the impact of this vulnerability is severe and potentially catastrophic for organizations relying on AcyMailing for their email marketing operations. An attacker who successfully exploits this flaw gains full control over the web server process running the application. This level of access typically allows the adversary to read sensitive data such as database credentials, user passwords stored in plaintext or weakly hashed formats, and proprietary business information contained within newsletters. Furthermore, the compromised system can be used as a pivot point for further attacks against internal network resources, deployed as part of a botnet for distributed denial-of-service attacks, or utilized to distribute malware to unsuspecting visitors who interact with the infected website. The ability to execute code remotely without authentication significantly lowers the barrier to entry for attackers, enabling automated scanning tools and opportunistic scripts to compromise vulnerable sites at scale across the internet.
The technical mechanism behind this exploitation often involves crafting a malicious HTTP request that injects shell commands or PHP code into parameters expected to contain safe data such as email addresses, SMTP hostnames, or subject lines. Because the application processes these inputs without adequate filtering against dangerous characters like semicolons, pipes, or backticks in contexts where they trigger system-level execution, the injected payload is executed by the server's interpreter. This aligns with common attack patterns observed in web application security assessments and is frequently mapped to MITRE ATT&CK techniques such as T1059 Command and Scripting Interpreter for initial access and lateral movement within compromised environments. The lack of input validation suggests a fundamental oversight in secure coding practices, where developers assumed that the context of data usage was safe or relied on client-side validations which can be easily bypassed by modifying requests directly at the network level using tools like Burp Suite or curl.
Mitigation strategies must prioritize immediate remediation through software updates and defensive configuration changes. The most effective solution is to upgrade AcyMailing SMTP Newsletter to a version greater than 11.0.5, where the vendor has presumably implemented proper input sanitization and output encoding techniques to prevent code injection. In cases where an immediate update is not feasible due to compatibility constraints or deployment cycles, temporary mitigations should include restricting access to WordPress admin areas via IP whitelisting if possible, although this may be challenging for cloud-hosted environments with dynamic IPs. Additionally, implementing a Web Application Firewall can help detect and block malicious payloads attempting to exploit known injection patterns before they reach the application logic. Security teams should also conduct thorough audits of other plugins installed on the same WordPress instance, as attackers often chain vulnerabilities or use one compromised component to escalate privileges across multiple applications sharing the same database credentials. Regular vulnerability scanning and monitoring for unusual outbound network traffic from the server can aid in early detection of exploitation attempts post-deployment.