CVE-2026-49939 in James
Summary
by MITRE • 11/06/2026
In Apache James server prior version 3.9.1 improper Access Control List processing is exposed by the JMAP protocol which do not account for negative rules positionned by IMAP protocol.
This results in users being able to administer folders in JMAP despite having being explicitly denied the right to do so in IMAP.
Users are recommended to upgrade to version 3.9.1 which fixes this issue.
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Analysis
by VulDB Data Team • 11/06/2026
The Apache James mail server, a widely deployed open-source Java-based SMTP and POP3/IMAP server, contains a critical access control vulnerability within its JMAP (JSON Meta Application Protocol) implementation prior to version 3.9.1. This flaw stems from an improper handling of Access Control Lists when the system processes requests via the JMAP protocol interface while simultaneously maintaining ACLs defined through the IMAP protocol. The core technical deficiency lies in the failure of the JMAP handler to correctly interpret or enforce negative rules that were established by users or administrators using standard IMAP commands. In typical mail server architectures, access control lists dictate which operations a user can perform on specific mailbox folders, such as reading, writing, deleting, or administering folder structures. When an administrator explicitly denies these administrative rights via the IMAP interface, those restrictions are stored in the underlying ACL database but are not properly validated by the JMAP endpoint during request processing.
This architectural inconsistency creates a significant security gap where authentication and authorization boundaries become blurred. Specifically, users who have been explicitly denied permission to administer folders through the IMAP protocol can bypass these restrictions when interacting with the server via the JMAP API. This allows unauthorized entities to perform administrative actions on mailboxes they do not own or manage, such as creating new subfolders, modifying folder metadata, or potentially deleting existing structures depending on the specific implementation details of the JMAP handlers involved. The vulnerability effectively undermines the principle of least privilege by allowing a user with limited IMAP permissions to escalate their capabilities through an alternative protocol interface that does not share the same strict enforcement logic for negative ACL rules.
The operational impact of this flaw is severe, particularly in multi-tenant environments or shared hosting scenarios where isolation between users is critical. An attacker who gains access to a low-privilege account can exploit this discrepancy to disrupt other users' mail services by manipulating folder structures they should not have access to. This could lead to denial-of-service conditions for affected mailbox owners if folders are deleted or corrupted. Furthermore, the ability to administer folders may facilitate further attacks, such as planting malicious filters that redirect emails from targeted accounts to attacker-controlled addresses, thereby compromising confidentiality and integrity of communications. The existence of this bypass also complicates forensic analysis and audit trails, as actions taken via JMAP might not align with expected permission logs derived from IMAP activity patterns.
From a standards perspective, this vulnerability maps directly to CWE-269 Improper Privilege Management, specifically involving the failure to enforce role-based access controls across different interfaces or protocols within the same application. It also relates to CWE-862 Missing Authorization, as the system fails to verify that the user has the necessary permissions for the specific action being requested via JMAP. In terms of the MITRE ATT&CK framework, this behavior aligns with T1078 Valid Accounts and potentially T1534 Internal Spearphishing if used to manipulate mail flows within an organization. The root cause is a lack of centralized or unified authorization logic that applies consistently across all supported protocols, leading to fragmented security enforcement where one protocol's restrictions are ignored by another.
To mitigate this risk, organizations running Apache James must upgrade immediately to version 3.9.1 or later, which includes the necessary patches to ensure that JMAP requests respect negative ACL rules defined via IMAP. Until an upgrade is feasible, administrators should consider restricting network access to the JMAP endpoint if it is not actively required for business operations, thereby reducing the attack surface available to potential exploiters. Additionally, implementing strict monitoring and logging of folder administration activities across both protocols can help in detecting anomalous behavior indicative of this exploitation attempt. Regular security audits focusing on cross-protocol permission consistency are recommended to identify similar architectural flaws in other enterprise mail systems that support multiple access methods.