OpenSSL Vulnerability Allows Tampering with CMS AuthEnvelopedData Messages
A vulnerability in OpenSSL, CVE-2026-34182, permits network-adjacent attackers to tamper with CMS AuthEnvelopedData messages by improperly validating integrity check values.
The Zero Day Initiative (ZDI) has disclosed a vulnerability in OpenSSL, tracked as ZDI-26-790 and CVE-2026-34182, that could allow network-adjacent attackers to tamper with CMS AuthEnvelopedData messages. This flaw stems from an improper validation of the integrity check value within the handling of AES-GCM message authentication codes.
To successfully exploit this vulnerability, an attacker must first possess the capability to modify CMS AuthEnvelopedData messages. Once this prerequisite is met, the attacker can leverage the improper integrity check to alter authenticated data within these messages. The specific technical mechanism involves a flaw in how OpenSSL processes the authentication tag generated by the AES-GCM authenticated encryption mode.
OpenSSL has released an update to address this vulnerability. Users are strongly advised to apply the patch as soon as possible to mitigate the risk of message tampering. The Common Vulnerability Scoring System (CVSS) rating for this vulnerability is 3.1, indicating a moderate level of severity. While exploitation requires a specific network position and the ability to intercept or modify traffic, the potential for data integrity compromise makes it a significant concern.
The disclosure timeline indicates that the vulnerability was initially reported to the vendor on April 9, 2026. Following a coordinated disclosure process, the advisory was publicly released on October 22, 2026, with an update to the advisory also published on the same date. This timeline suggests a thorough vetting and patching process.
This vulnerability affects the security of data that relies on the integrity guarantees provided by CMS AuthEnvelopedData. This data format is used in various security protocols and applications where authenticated encryption is crucial for protecting both confidentiality and integrity. Tampering with these messages could lead to various security breaches, depending on the context in which OpenSSL is used.
The vulnerability was discovered and reported by TrendAI, with the Zero Day Initiative facilitating the coordinated public release. This collaboration highlights the ongoing efforts by security researchers and organizations like ZDI to identify and address vulnerabilities in widely used cryptographic libraries.
While the CVSS score is moderate, the implications of compromised data integrity can be severe. Organizations utilizing OpenSSL for secure communication or data storage should prioritize updating their systems to the patched versions. Network-adjacent attackers could potentially manipulate critical data, leading to system malfunctions or security bypasses.
Further technical details and mitigation guidance can be found in the official advisory and the OpenSSL security advisory. The prompt patching of this vulnerability is essential to prevent potential exploitation and maintain the security of systems relying on OpenSSL's cryptographic functions.