Description

openssl_encrypt versions before 1.4.9 use a denylist to identify trusted built-in plugins, allowing unsigned plugins in top-level plugins/ directories and unknown subdirectories to bypass signature verification. Attackers can place malicious unsigned plugins following documented installation paths to achieve arbitrary code execution in the CLI process with access to passwords and cryptographic keys.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.8",
  "pubDate": "2026-08-27T17:21:00.533Z",
  "pubdate": "2026-08-27T17:21:00.533Z",
  "executiveSummary": "The openssl_encrypt library, in versions prior to 1.4.9, contains a critical security flaw involving insecure plugin validation logic. The vulnerability stems from the use of an ineffective denylist-based mechanism for identifying trusted built-in plugins, which fails to enforce strict cryptographic signature verification.\nThis flaw allows for the loading of unsigned, malicious plugins located within top-level 'plugins/' directories or arbitrary subdirectories. An attacker can leverage this misconfiguration to achieve arbitrary code execution within the context of the CLI process.\nThe successful exploitation of this vulnerability grants an attacker unauthorized access to sensitive information, specifically cryptographic keys and stored passwords accessible by the process. Given the nature of the library, the risk implication is severe, as it facilitates full compromise of the application's security posture and the secrets it manages.\nNo specific authentication or specialized privileges are mentioned as requirements for this exploit, provided the attacker can influence the filesystem or installation path of the target environment. The vulnerability represents a bypass of primary security controls intended to ensure code integrity and system trustworthiness.",
  "technicalDetails": "The root cause of this vulnerability lies in the implementation of a denylist security model within the openssl_encrypt plugin loading mechanism. Rather than employing a robust allowlist or mandatory signature verification, the library checks plugins against a list of known 'trusted' components. This logic is inherently flawed as it defaults to trusting any plugin not explicitly excluded, thereby permitting the execution of unsigned or malicious binaries.\nThe vulnerable component resides within the plugin discovery and loading subsystem of openssl_encrypt, specifically in how the library traverses directory structures. Because the verification logic does not restrict plugin loading to authorized, cryptographically signed files, it permits the execution of files located in the 'plugins/' top-level directory or any unknown subdirectories accessible by the application.\nThe attack flow proceeds as follows: First, an attacker identifies a target installation path where the openssl_encrypt CLI process expects plugin modules. Second, the attacker places a crafted, unsigned malicious plugin payload into the 'plugins/' directory or a nested subdirectory. Third, upon the next execution or initialization of the CLI process, the application automatically scans these directories and loads the attacker-controlled code into its own memory space.\nBecause the library fails to validate the cryptographic signature, the operating system and the CLI process treat the malicious plugin as a legitimate extension. Once loaded, the malicious plugin executes with the same privilege level as the CLI process. This provides the attacker full visibility into the runtime environment, allowing for the exfiltration of sensitive cryptographic material, such as private keys and plaintext passwords residing in memory.\nThis vulnerability affects all versions of openssl_encrypt prior to 1.4.9. Exploitation is facilitated by the library's permissive search path logic, which does not differentiate between cryptographically verified assets and attacker-injected files. The post-exploitation impact includes complete loss of confidentiality and integrity regarding the secrets managed by the application, effectively bypassing any downstream security controls that rely on the integrity of the CLI process for key management or encryption operations."
}