CVE-2025-13516
Published: 02 December 2025
Description
The SureMail – SMTP and Email Logs Plugin for WordPress is vulnerable to Unrestricted Upload of File with Dangerous Type in versions up to and including 1.9.0. This is due to the plugin's save_file() function in inc/emails/handler/uploads.php which duplicates all…
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email attachments to a web-accessible directory (wp-content/uploads/suremails/attachments/) without validating file extensions or content types. Files are saved with predictable names derived from MD5 hashes of their content. While the plugin attempts to protect this directory with an Apache .htaccess file to disable PHP execution, this protection is ineffective on nginx, IIS, and Lighttpd servers, or on misconfigured Apache installations. This makes it possible for unauthenticated attackers to achieve Remote Code Execution by uploading malicious PHP files through any public form that emails attachments, calculating the predictable filename, and directly accessing the file to execute arbitrary code granted they are exploiting a site running on an affected web server configuration.
Mitigating Controls (NIST 800-53 r5)AI
Directly addresses the lack of file extension and content type validation in the plugin's save_file() function, preventing storage of malicious PHP files in the web-accessible directory.
Requires restrictions on access to publicly accessible content in wp-content/uploads/suremails/attachments/, blocking unauthenticated attackers from directly accessing predictable MD5-named malicious files.
Mandates secure web server configuration settings to disable PHP execution in upload directories, mitigating ineffective .htaccess protections on nginx, IIS, Lighttpd, and misconfigured Apache servers.
Security SummaryAI
CVE-2025-13516 is an unrestricted upload of file with dangerous type vulnerability affecting the SureMail – SMTP and Email Logs Plugin for WordPress in versions up to and including 1.9.0. The issue stems from the plugin's save_file() function in inc/emails/handler/uploads.php, which duplicates all email attachments to the web-accessible directory wp-content/uploads/suremails/attachments/ without validating file extensions or content types. Files are stored with predictable names derived from MD5 hashes of their content. Although the plugin includes an Apache .htaccess file in this directory to disable PHP execution, this protection fails on nginx, IIS, and Lighttpd servers, as well as misconfigured Apache setups. The vulnerability was published on 2025-12-02 and carries a CVSS v3.1 base score of 8.1 (AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H), mapped to CWE-434.
Unauthenticated attackers can exploit this flaw by submitting malicious PHP files as attachments through any public form on the site that triggers an email. By calculating the predictable MD5-based filename of the uploaded file, attackers can directly access and execute the malicious code via a web request, achieving remote code execution on affected server configurations. The attack requires no privileges but depends on the target site's web server not enforcing the .htaccess protections.
References include the CWE-434 definition and WordPress plugin trac links to the affected code in plugin.php and uploads.php, along with changeset 3403145, which documents changes to the trunk that may address the vulnerability.
Details
- CWE(s)
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Unrestricted file upload vulnerability in public-facing WordPress plugin enables unauthenticated RCE via malicious PHP webshells, directly facilitating T1190 (Exploit Public-Facing Application) and T1100 (Web Shell).