Description

openssl_encrypt before 1.4.9 executes untrusted third-party plugins with insufficient controls: the plugin signature policy defaulted to WARN, so an unsigned/unverifiable non-built-in plugin was compiled and executed in the host process at import time, before the runtime sandbox is installed. The only default gate was an incomplete, bypassable AST denylist. If a user is induced to load an attacker's plugin, this results in arbitrary code execution with the privileges of the user running openssl_encrypt. Fixed in 1.4.9 by defaulting the signature policy to ENFORCE for non-built-in plugins.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.8",
  "pubDate": "2026-08-27T17:21:02.320Z",
  "pubdate": "2026-08-27T17:21:02.320Z",
  "executiveSummary": "The openssl_encrypt library prior to version 1.4.9 contains a critical vulnerability stemming from insecure handling of third-party plugins. By defaulting the signature verification policy to a 'WARN' state, the library permits the execution of unsigned or unverifiable code within the host process at import time. This execution occurs prior to the initialization of the runtime security sandbox, effectively bypassing intended security controls. An attacker capable of inducing a user to load a malicious plugin can achieve arbitrary code execution, inheriting the full privilege level of the host process user. The vulnerability is characterized by an insufficient AST-based denylist, which fails to act as a robust security boundary. The primary risk implication is a total system compromise if the host process operates with elevated permissions or within a sensitive environment. Exploitation requires user interaction to facilitate the loading of the malicious plugin, after which the library's flawed policy enforcement mechanism facilitates weaponization.",
  "technicalDetails": "The vulnerability originates from the architectural decision within openssl_encrypt to perform plugin initialization and compilation at import time before the application's runtime sandbox is fully instantiated. In versions prior to 1.4.9, the signature verification policy for third-party plugins was set to 'WARN' by default. This design choice permitted the execution of unsigned, unverifiable, or untrusted plugins within the host memory space.\nThe technical attack flow begins when an attacker provides a malicious plugin to a victim. When the victim’s environment attempts to import or load this plugin, the openssl_encrypt library initiates a compilation process. Because the signature policy is configured to 'WARN', the system logs the lack of a valid signature but proceeds to execute the plugin code. Since this occurs at import time, the sandbox—which is intended to restrict the capabilities of loaded code—has not yet been initialized. This creates a race condition and a privilege escalation vector where the plugin operates with the full execution context and permissions of the host process.\nFurthermore, the library attempted to mitigate risks using an AST (Abstract Syntax Tree) denylist. This mechanism is fundamentally insufficient as it is easily bypassed by obfuscated code or alternative syntax structures that fall outside the defined denylist parameters. The absence of strict enforcement (ENFORCE) means that any plugin not explicitly signed by a trusted authority is treated as legitimate, provided it avoids the flawed denylist.\nUpon successful exploitation, the payload executes within the address space of the target process. This allows for arbitrary code execution, which can be leveraged to extract sensitive cryptographic material, exfiltrate data from the host, or establish persistence within the execution environment. The vulnerability affects all versions of openssl_encrypt prior to 1.4.9. Successful execution does not require explicit authentication to the library itself, but rather relies on the user's implicit trust in the plugin source, leveraging the privileges associated with the user account running the process."
}