CVE-2026-44695: Outline: Slack OAuth state can link a victim Outline account to an attacker Slack identity

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-05-11 · updated 2026-06-17
Weakness: CWE-352

Description

Outline is a service that allows for collaborative documentation. Prior to 1.7.1, the Slack integration callback for GET /auth/slack.post accepts an unsigned, session-independent OAuth state value. A third party who can obtain a Slack OAuth code for the same Outline Slack client can make a logged-in Outline user complete the callback and link that user's Outline account to the attacker's Slack team_id and user_id. The linked Slack identity can then use the Slack /outline search command as the victim Outline user. This vulnerability is fixed in 1.7.1.

Affected products

outline: before 1.7.1 — fixed in 1.7.1

How to fix

Upgrade to a fixed version: outline 1.7.1. Check the vendor advisory for mitigations.

References

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