Plane EUVD-2026-98819

Applies only to self-hosted Plane deployments running a version prior to 1.4.0, where the WorkspaceJoinEndpoint (api/workspaces/{slug}/invitations/{pk}/join/) serves unauthenticated GET requests and the pre-fix WorkSpaceMemberInviteSerializer exposes the token and get_invite_link fields - this is the default behavior, no special feature toggle is required. The practical limiting factor is that the attacker must know or successfully enumerate a valid workspace slug and a pending invitation's primary key (pk) to retrieve a usable token, and the stolen access is bounded to the specific role assigned to that invitation rather than arbitrary privilege. No authentication and no user interaction are required (PR:N/UI:N).

This is a moderate, real-but-not-urgent issue. The provided CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N, base 6.5) indicates a network-reachable, low-complexity, unauthenticated flaw with partial confidentiality and integrity impact and no availability impact - consistent with the CWE-200 information-disclosure classification and the description of an unauthenticated GET leaking a secret invitation token. No EPSS score, KEV listing, SSVC decision, or POC was provided in the input, so there is no signal of active exploitation or automated weaponization: exploitation status is 'no public exploit identified at time of analysis.' The main factor that tempers the PR:N/AC:L reading is that successful exploitation requires knowing or enumerating a valid invitation primary key (pk) and workspace slug for a pending invite, and the impact is bounded to the role assigned to that specific invitation rather than full admin takeover - so this is a targeted membership-hijack / token-leak issue, not a wormable mass-compromise. Net: a legitimate patch-priority item for self-hosted Plane operators (especially those with open signup or sensitive workspaces), but not a drop-everything emergency absent exploitation evidence.

An external attacker who learns or enumerates a pending invitation's identifier sends an unauthenticated GET to api/workspaces/{slug}/invitations/{pk}/join/, and the WorkSpaceMemberInviteSerializer returns the secret invitation token (directly and via get_invite_link). The attacker then submits that token to the invitation-acceptance flow to join the victim's workspace with the invited role, without ever having received the invitation. No public exploit code was identified in the provided data.