CVE-2026-121729 in emailflare
Summary
by MITRE • 11/04/2026
emailflare before commit cf31f33 contains a missing authorization vulnerability in the inbox service /api/keys routes that allows any authenticated member to list, create and revoke API keys. Attackers can mint a global live API key accepted by /v1/send to send mail from any domain, or revoke existing keys to disable integrations.
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Analysis
by VulDB Data Team • 11/04/2026
The vulnerability identified in the emailflare application prior to commit cf31f33 represents a critical failure in access control mechanisms within its inbox service, specifically targeting the API key management endpoints located at /api/keys. This flaw is classified as an Insecure Direct Object Reference or more accurately, a Broken Access Control issue where the server fails to verify that the authenticated user requesting an action has the appropriate permissions for the specific resource being accessed. Instead of restricting operations such as listing, creating, and revoking API keys to only those users who own the associated account or possess administrative privileges over the target domain, the system allows any authenticated member to perform these actions on any other member's resources. This lack of server-side authorization checks creates a significant security gap that undermines the integrity and confidentiality of user data and service functionality.
From an operational perspective, this vulnerability enables two distinct categories of malicious activity depending on the attacker's intent. First, attackers can exploit the ability to create API keys by minting global live API keys that are accepted by the /v1/send endpoint. These keys allow the sender to send emails from any domain configured within the platform, effectively bypassing standard authentication and authorization checks for email sending operations. This capability facilitates large-scale spam campaigns, phishing attacks, or business email compromise scenarios where an attacker impersonates legitimate entities without needing access to their actual credentials. The use of live API keys ensures that these malicious actions are executed with full privileges granted by the platform, making detection more difficult as the traffic appears legitimate from a protocol standpoint.
Secondly, attackers can leverage the revocation functionality to disrupt service availability for other users. By identifying and deleting existing API keys belonging to other authenticated members, an attacker can disable critical integrations that rely on these keys for automated email delivery or monitoring purposes. This constitutes a denial of service attack against specific user workflows rather than the entire platform infrastructure. The impact extends beyond immediate disruption as it may lead to data loss if dependent systems fail to handle key revocation gracefully, and it erodes trust in the platform's reliability among enterprise customers who depend on consistent API availability for their business operations.
This vulnerability aligns with CWE-284 Improper Access Control, specifically reflecting scenarios where access control is not enforced correctly during resource manipulation. In terms of offensive security frameworks, this behavior maps to MITRE ATT&CK technique T1078 Valid Accounts, as the attacker utilizes legitimate credentials to perform unauthorized actions, and potentially T1539 Steal Web Session Cookie if session hijacking was involved in obtaining those initial valid accounts. The core issue lies not in authentication but in authorization logic, highlighting a common pitfall where developers assume that being logged into the application is sufficient proof of permission for all subsequent API calls without verifying resource ownership or role-based access rights on each request.
To mitigate this vulnerability and prevent similar issues in future development cycles, it is imperative to implement strict server-side authorization checks on all endpoints within the /api/keys route. Each request must validate that the authenticated user making the call owns the specific API key being accessed, created, or revoked. This can be achieved by binding resource identifiers directly to user accounts in the database and verifying this relationship before executing any state-changing operations. Additionally, implementing role-based access control policies ensures that only users with explicit administrative privileges over a domain can manage its associated keys. Regular security audits focusing on authorization logic, along with automated testing using tools designed to detect broken object level vulnerabilities, are essential for maintaining robust application security posture and protecting user data from unauthorized manipulation.