CVE-2026-66885: Livebook: CSRF binds victim session to attacker

Cross-Site Request Forgery (CSRF) vulnerability in livebook-dev livebook allows an attacker to authenticate a victim's browser session under the attacker's own Livebook Teams identity. When Livebook is configured to use Livebook Teams for identity, Livebook.ZTA.LivebookTeams.handle_request/4 in lib/livebook/zta/livebook_teams.ex handles the OAuth-style callback carrying a teams_identity marker and a code parameter. The clause exchanges that code for an access token and writes the token into the browser session without verifying any value that ties the callback to the browser session that started the login. No state or nonce is generated when the flow is initiated: Livebook.Teams.Requests.create_auth_request/1 in lib/livebook/teams/requests.ex sends an empty request body, so no per-attempt value is ever registered, and the callback clause has nothing to compare against. An attacker who holds membership in the same Livebook Teams organisation as the target instance can therefore begin the login flow themselves, retain the resulting authorization code without redeeming it, and induce a victim to open a crafted URL carrying that code. The victim's browser completes the exchange and the resulting session is bound to the attacker's identity rather than the victim's. The victim is not required to hold any particular privilege, and no credential belonging to the victim is involved. The vulnerability does not allow the attacker to authenticate as the victim. The consequence is that a user believes they are working in their own authenticated session while they are in fact operating as another identity. Work performed in that session is attributed to the attacker's account, and secrets, uploaded data, or notebook results the victim produces are exposed to the attacker rather than kept in the victim's own account. The authorization code must be redeemed within a short window after the login flow begins, which constrains the timing of the attack but not its feasibility. This issue affects livebook: from 0.15.0 before 0.18.7 and from 0.19.0 before 0.19.9.

An attacker who is a legitimate member of an organisation's Livebook Teams workspace initiates the Livebook Teams login flow themselves, generating a valid authorization code, but instead of completing their own login they hold onto the code. They then craft a URL embedding that code and send it to a target colleague via a plausible pretext — a chat DM claiming it's a shared notebook link, or a phishing email mimicking a Livebook session-recovery notification. The colleague, believing they are logging into their own Livebook workspace, clicks the link; their browser silently exchanges the attacker's code for an access token and stores it in their session before the code expires. The victim then works normally in Livebook — uploading a dataset, running a model training notebook, pasting an API key into a code cell — unaware that everything they do is recorded under the attacker's Livebook Teams identity, giving the attacker later access to that data and those secrets through their own account.