Description

OpenSSL has addressed a high-severity security vulnerability identified as CVE-2025-15467, which introduces a pre-authentication risk of denial-of-service and potential remote code execution. The flaw exists in the handling of Cryptographic Message Syntax (CMS) data and can be triggered by a specially crafted message without requiring prior authentication. Given OpenSSL’s widespread use across enterprise servers, security appliances, and cryptographic services, successful exploitation could have broad operational and security implications. The vulnerability stems from improper bounds checking during the parsing of CMS AuthEnvelopedData structures that use AEAD (Authenticated Encryption with Associated Data) ciphers, such as AES-GCM. When OpenSSL processes these CMS messages, it copies the Initialization Vector (IV) provided in the ASN.1 parameters into a fixed-size stack buffer. The code fails to adequately validate the IV length before the copy operation. An attacker can exploit this flaw by supplying a malicious CMS payload containing an oversized IV. Because the overflow occurs prior to cryptographic authentication or integrity verification, the attack can be launched pre-authentication. The resulting stack buffer overflow may cause the affected application to crash, leading to a denial-of-service condition. In environments lacking modern exploit mitigations, the overflow could theoretically be leveraged to achieve remote code execution. The vulnerability affects OpenSSL versions in the 3.x branch, including long-term supported releases, while older legacy versions are not impacted by this specific issue. Systems that automatically process untrusted CMS or PKCS#7 data such as email gateways, S/MIME services, certificate authorities, and security tooling—are at heightened risk. OpenSSL has released patches that introduce proper length validation to prevent out-of-bounds memory writes. Organizations are strongly advised to update affected OpenSSL versions promptly, review applications that rely on CMS parsing, and ensure standard exploit mitigations such as stack canaries and address space layout randomization are enabled. Early remediation is critical to reducing exposure to this pre-authentication attack vector.