WPvivid Backup & Migration plugin, with more than 900,000 active installations, has patched a critical vulnerability (CVE-2026-1357) that could result in Remote Code Execution through an unauthenticated arbitrary file upload. The flaw, which carries a CVSS score of 9.8, affects versions up to and including 0.9.123.
The issue is considered critically exploitable only on websites where administrators enabled the backup transfer functionality by generating a key that allows backups to be sent from another site. This option is turned off by default, and any generated key can remain valid for no longer than 24 hours.
The issue was discovered by security researcher Lucas Montes, also known as NiRoX, and responsibly disclosed through the Wordfence Bug Bounty Program, earning him a reward of $2,145.
Root Cause of the Vulnerability
According to the Wordfence disclosure, the vulnerability was traced to improper error handling during RSA decryption and inadequate validation of uploaded files. “ This is due to improper error handling in the RSA decryption process combined with a lack of path sanitization when writing uploaded files. “
When decryption of a session key failed, the plugin did not halt execution and instead proceeded with a null-byte key. “When the plugin fails to decrypt a session key using openssl_private_decrypt(), it does not terminate execution and instead passes the boolean false value to the phpseclib library’s AES cipher initialization. The library treats this false value as a string of null bytes, allowing an attacker to encrypt a malicious payload using a predictable null-byte key.”
The plugin also did not properly sanitize filenames from decrypted data, making directory traversal possible. This could enable unauthenticated attackers to upload arbitrary PHP files to publicly accessible locations and achieve remote code execution as highlighted: “ This makes it possible for unauthenticated attackers to upload arbitrary PHP files to publicly accessible directories and achieve Remote Code Execution via the wpvivid_action=send_to_site parameter.”
The Patch
The WPvivid team has patched the vulnerability in version 0.9.124 by adding an empty check to the $key value in the decrypt_message() function, and also implemented a file extension check, which restricts uploads to approved backup file types only.