CVE-2026-114655 in libmongocrypt
Summary
by MITRE • 10/22/2026
libmongocrypt builds requests to external key management services (AWS, Azure and GCP) by inserting values from key vault documents, KMS provider configuration and KMS responses into request lines, headers and signed request bodies without validating or encoding them for each context. A user with write access to the key vault collection can alter the structure of these requests, including adding members to request bodies and token claims that the library then signs with the application's credentials. This may result in key management operations being performed with parameters the application did not intend.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified within libmongocrypt represents a critical server-side request forgery flaw rooted in insufficient input validation during the construction of HTTP requests for external Key Management Services such as AWS, Azure, and Google Cloud Platform. The core technical deficiency lies in the library's mechanism for assembling these requests, where it directly injects values extracted from key vault documents, KMS provider configurations, and responses received from the KMS providers into various components of the outgoing request. These components include HTTP headers, signed request bodies, and specific parameter fields within the API calls themselves. Crucially, the library fails to validate or encode these injected values according to the syntactic requirements of each context before inclusion. This lack of sanitization creates a direct pathway for attackers who possess write access to the MongoDB key vault collection to manipulate the structure and content of requests sent to cloud-based KMS endpoints.
From an operational perspective, this flaw allows an attacker with compromised or maliciously controlled credentials in the application's database to alter the behavior of cryptographic operations without needing direct access to the external cloud provider accounts. By modifying documents within the key vault collection, a user can inject arbitrary data into request bodies and token claims. Because libmongocrypt signs these requests using the application's own service account credentials, the KMS providers will treat these manipulated requests as legitimate commands issued by the authorized entity. This effectively bypasses authentication checks at the cloud provider level, as the signature is valid for the modified payload. The attacker can thus force the key management service to perform operations that were not intended by the application developers or administrators, such as decrypting data with different keys, rotating encryption keys prematurely, or potentially exposing sensitive cryptographic material through misconfigured access policies triggered by the forged requests.
The security implications are severe, particularly in environments where multi-tenancy is present or when database users have elevated privileges that should not extend to modifying key vault metadata. The ability to alter signed request bodies means that an attacker can change parameters such as encryption algorithms, key IDs, or access permissions associated with the keys managed by the KMS. This could lead to data integrity violations if weaker cryptographic standards are forced upon encrypted fields, or it could result in denial of service if valid keys are rendered inaccessible through malicious configuration changes. Furthermore, because the requests are signed with legitimate credentials, they may evade standard security monitoring tools that rely on signature validation rather than semantic analysis of request content. This aligns closely with CWE-94 Improper Control of Generation of Code Command Injection and CWE-20 Poor Input Validation, as the root cause is the failure to restrict or sanitize data inputs before their use in a command context.
In terms of threat modeling, this vulnerability facilitates actions consistent with MITRE ATT&CK technique T1556 Modifying Authentication Process, specifically by manipulating credentials or tokens used for authentication against external services. It also relates to T1078 Valid Accounts, as the attacker leverages legitimate database access to abuse cloud service permissions. The attack vector is primarily local within the application's data layer but has remote consequences via the network calls made to AWS, Azure, and GCP APIs. This highlights a significant risk in architectures where database integrity directly influences security-critical infrastructure operations like key management.
To mitigate this vulnerability, immediate remediation should focus on implementing strict validation and encoding of all values sourced from external inputs before they are incorporated into HTTP requests. Developers must ensure that data extracted from the MongoDB key vault is validated against expected schemas and encoded appropriately for its specific context within the request structure, such as URL-encoding parameters or properly escaping JSON fields to prevent structural manipulation. Additionally, implementing least privilege principles in database access controls can limit the impact by restricting write access to the key vault collection to only those processes that absolutely require it. Regular security audits of data handling routines and integration testing with fuzzing tools designed for HTTP request construction can help identify similar flaws before deployment. Updating libmongocrypt to a patched version that addresses this input validation gap is essential, along with reviewing existing database permissions to ensure no unauthorized users retain write access to sensitive configuration collections.