CVE-2026-81703 in openssl_encrypt
Summary
by MITRE • 08/27/2026
openssl_encrypt versions before 1.4.9 fail to validate encryption status of embedded post-quantum private keys in file metadata. Attackers can craft files with unencrypted embedded PQC keys that decrypt under any password, bypassing authentication and producing attacker-chosen plaintext with false integrity verification.
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Analysis
by VulDB Data Team • 08/27/2026
The vulnerability identified in openssl_encrypt versions prior to 1.4.9 represents a critical failure in the cryptographic implementation of file metadata handling, specifically concerning post-quantum cryptography (PQC) keys. This flaw stems from an insufficient validation mechanism when processing embedded private keys within encrypted containers. In standard secure implementations, any modification or decryption attempt must strictly verify that the underlying data has not been tampered with and that the encryption status is authentic before proceeding with key extraction or usage. However, in these affected versions, the software fails to rigorously validate whether an embedded post-quantum private key was originally encrypted using a password-based scheme or if it exists as plaintext within the metadata structure. This oversight creates a significant gap between the intended security model and the actual runtime behavior of the library.
From a technical perspective, this defect allows attackers to craft malicious files where the embedded PQC keys are stored in an unencrypted state despite being placed in sections that should enforce encryption integrity checks. When such a file is processed by vulnerable instances of openssl_encrypt, the system incorrectly assumes the key material has undergone proper authentication and decryption procedures. Consequently, the library proceeds to decrypt or expose these keys without requiring valid credentials. This behavior effectively bypasses password-based authentication mechanisms designed to protect sensitive cryptographic materials. The root cause lies in the lack of strict state verification during the parsing phase, where the application does not cross-reference the encryption flag with the actual ciphertext status of the embedded key data.
The operational impact of this vulnerability is severe, as it leads directly to unauthorized access and potential compromise of secure communications or stored secrets. Attackers can exploit this flaw by constructing specially crafted input files containing unencrypted PQC keys that are accepted as valid under any provided password string. This means that even if a user provides an incorrect or random password, the system may still successfully decrypt the key material because it is not actually encrypted in the first place within the malicious payload. Furthermore, this bypass extends to integrity verification processes; since the decryption succeeds without proper authentication, the resulting plaintext appears valid and untampered, leading downstream applications to trust data that was intentionally crafted by an adversary. This undermines both confidentiality and integrity guarantees provided by the cryptographic suite.
This vulnerability aligns with CWE-327, which describes the use of a broken or risky cryptographic algorithm, specifically in the context of improper key management and authentication bypasses due to flawed implementation logic. It also maps closely to MITRE ATT&CK technique T1558, particularly sub-technique T1558.004 related to Steal or Forge Kerberos Tickets via Golden Ticket attacks if applied to identity systems, but more broadly fits under general cryptographic bypass patterns where authentication controls are circumvented through malformed inputs. The exploitation vector typically involves social engineering or supply chain compromise to deliver the crafted file, followed by automated processing that triggers the vulnerable code path within openssl_encrypt.
Mitigation strategies must prioritize immediate upgrading of the openssl_encrypt library to version 1.4.9 or later, where this validation logic has been corrected to enforce strict checks on encryption status before exposing key material. In environments where an upgrade is not immediately feasible, administrators should implement input sanitization layers that reject files with suspicious metadata structures or unexpected plaintext indicators in encrypted sections. Additionally, enabling comprehensive logging and monitoring for decryption failures can help detect attempted exploitation activities. Security teams should also review their cryptographic workflows to ensure that no legacy modes of operation are being used inadvertently, as these often lack the rigorous state validation present in modern implementations. Regular audits of third-party dependencies and continuous integration testing with fuzzing tools targeting metadata parsing routines will further reduce the risk surface associated with such implementation flaws.