CVE-2026-84962 in libmongocrypt
Summary
by MITRE • 09/03/2026
An unauthorized user with key vault write access may cause an authorized client to issue arbitrary authenticated Google Cloud KMS API calls under the authorized user's identity, escalating database-level access into cloud key control and defeating client-side encryption.
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Analysis
by VulDB Data Team • 09/03/2026
The vulnerability described represents a critical authorization bypass within Google Cloud Key Management Service (KMS) that exploits the relationship between Identity and Access Management policies and cryptographic operations. Specifically, it allows an entity with write permissions to a secret or configuration in a key vault to manipulate the context under which authorized clients execute API calls against KMS resources. This flaw effectively decouples the identity of the actor initiating the request from the intended scope of their privileges, enabling privilege escalation that transcends standard database-level access controls. The core technical issue lies in how the system validates and processes authentication tokens or service account credentials when interacting with key management endpoints after a write operation has been performed on associated vault configurations.
From a technical perspective, this vulnerability likely stems from improper validation of resource ownership or context isolation during cryptographic operations. When an unauthorized user modifies settings within a key vault, they may be able to alter metadata, policy bindings, or routing information that influences how subsequent requests are authenticated and authorized by the KMS service layer. This manipulation allows them to trick legitimate clients into using their own credentials or compromised service account tokens to perform actions such as decrypting data, generating new keys, or modifying key policies under the guise of an authorized user. The system fails to enforce strict separation between administrative configuration changes and cryptographic execution contexts, leading to a situation where write access translates directly into control over sensitive cryptographic material.
The operational impact of this vulnerability is severe, particularly for organizations relying on client-side encryption models. In such architectures, data is encrypted before it leaves the application layer using keys managed by KMS, ensuring that even cloud providers cannot read the plaintext data. By gaining the ability to issue arbitrary authenticated API calls under an authorized user's identity, attackers can potentially decrypt stored sensitive information, exfiltrate cryptographic keys, or create new keys for their own use without detection. This defeats the primary security guarantee of client-side encryption, as the integrity and confidentiality of the encrypted payload are compromised through manipulation of the key management infrastructure rather than direct access to the data storage layer.
This type of flaw aligns with CWE-269 Improper Privilege Management and CWE-754 Improper Check for Unusual or Exceptional Conditions within the Common Weakness Enumeration framework, as it involves a failure in validating user roles during critical security operations. In terms of MITRE ATT&CK mapping, this behavior corresponds to T1098.002 SSH Authorized Keys Modification and potentially T1534 Internal Spearphishing if used for lateral movement, but more accurately reflects T1652 Client-Side Encryption Bypass or general privilege escalation techniques like T1078 Valid Accounts when the attacker leverages stolen or manipulated credentials to perform unauthorized administrative actions. The attack vector typically involves initial access through a compromised service account with limited write permissions that are then escalated via this configuration flaw.
Mitigation strategies must focus on enforcing strict least-privilege principles and implementing robust separation of duties between key management administration and data processing operations. Organizations should review IAM policies to ensure that users or services with write access to vault configurations do not possess implicit privileges that allow them to influence cryptographic execution contexts. Implementing additional verification steps, such as requiring multi-factor authentication for critical KMS API calls or using dedicated service accounts with narrowly scoped permissions for key rotation and policy changes can reduce the attack surface. Furthermore, enabling comprehensive audit logging and monitoring for anomalous patterns in KMS usage, particularly requests originating from unexpected sources or involving unusual combinations of vault modifications followed by immediate cryptographic operations, is essential for early detection and response to such exploitation attempts.