CVE-2026-104978 in Plane
Summary
by MITRE • 10/05/2026
Plane is an open-source project management tool. Prior to 1.4.0, Plane's project invitation list endpoint is accessible to any authenticated user who knows the workspace slug and project ID, while the public project invitation join endpoint accepts an invitation based only on a submitted email address. When a pending invitation targets an email address that has not registered with Plane, an attacker can enumerate the invitation, register an account using the invited email without mailbox verification, and accept the invitation. The attacker-controlled account is then added to the target workspace and project. This issue is fixed in 1.4.0.
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Analysis
by VulDB Data Team • 10/05/2026
The vulnerability identified in Plane versions prior to 1.4.0 represents a critical failure in access control mechanisms within an open-source project management platform, specifically affecting how user invitations are processed and validated. The core technical flaw stems from two distinct but related misconfigurations: the first involves the project invitation list endpoint being accessible to any authenticated user who possesses the workspace slug and project ID, while the second concerns the public project invitation join endpoint which accepts an invitation based solely on a submitted email address without requiring additional verification tokens or secure identifiers. This architectural weakness allows for unauthorized enumeration of pending invitations within specific workspaces and projects, provided the attacker has valid authentication credentials and knows the target identifiers.
The operational impact of this vulnerability is significant as it facilitates account takeover and unauthorized workspace infiltration through social engineering combined with automated enumeration techniques. When a pending invitation targets an email address that does not yet have a registered account in Plane, the system allows any user to submit that specific email address to the join endpoint. Upon submission, if the invitation exists for that email, the attacker can register a new account using the invited email without undergoing standard mailbox verification processes. This bypass of identity confirmation is particularly dangerous because it assumes that possession of an email address during registration equates to ownership or authorization, ignoring the fact that the invitation was intended for a specific individual who may not be aware they were targeted.
Once the attacker registers and accepts the invitation using the unverified email, their newly created account is immediately added to the target workspace and project with whatever permissions are associated with that invitation role. This effectively grants the attacker access to sensitive project data, collaboration history, and potentially other team members' information depending on the scope of the invited role. The ability to enumerate invitations means an adversary can systematically probe different email addresses against known or guessed workspace slugs and project IDs to discover valid pending invites, turning a simple invitation feature into a vector for reconnaissance and unauthorized access.
From a security standards perspective, this vulnerability aligns with CWE-284 Improper Access Control, as the application fails to restrict information disclosure and user registration actions based on proper authorization checks. It also relates to CWE-613 Insufficient Session Expiration or CWE-798 Use of Hard-coded Credentials if one considers the static nature of email-based validation without dynamic tokens. In terms of MITRE ATT&CK, this behavior supports techniques such as T1078 Valid Accounts for initial access and potentially T1552 Unsecured Credentials if the invited user's credentials are compromised later due to weak password policies associated with these auto-created accounts. The lack of multi-factor authentication or email confirmation before granting workspace membership exacerbates the risk, allowing attackers to establish a persistent foothold within organizational structures without detection.
Mitigation for this issue was implemented in version 1.4.0 by correcting the access control logic on both endpoints. To prevent similar vulnerabilities in other systems, it is essential that invitation mechanisms require unique, cryptographically secure tokens rather than relying solely on email addresses for validation. Additionally, any endpoint returning list data of pending invitations should enforce strict authorization checks ensuring only users with administrative privileges or specific project management roles can view such lists. For organizations using Plane versions prior to 1.4.0, immediate upgrading is required. Furthermore, administrators should review existing workspace memberships and remove any accounts that were created through suspicious invitation acceptance patterns, particularly those lacking proper email verification history. Implementing rate limiting on registration endpoints and enforcing mandatory email confirmation before granting access would further harden the system against automated enumeration attacks.