CVE-2026-43890: Outline is a service that allows for collaborative documentation. From 0.84.0 to 1.7.0, the subscriptions.create API endpoint in server/routes/api/sub...

Description

Outline is a service that allows for collaborative documentation. From 0.84.0 to 1.7.0, the subscriptions.create API endpoint in server/routes/api/subscriptions/subscriptions.ts exhibits a broken authorization pattern. When both collectionId and documentId are supplied in the request, the route handler authorizes ONLY the collection branch (line 125 if (collectionId)), while the downstream subscriptionCreator command at server/commands/subscriptionCreator.ts writes the subscription against the documentId (which was never validated). The result is a subscription record pinning the attacker's user to a victim document the attacker has no read access to, on any team in the instance. The schema (server/routes/api/subscriptions/schema.ts) only enforces "at least one of collectionId/documentId" via .refine() — it does NOT enforce mutual exclusivity, so passing both is a valid, schema-conforming request. This vulnerability is fixed in 1.7.1.

Metrics

CVSS 3.1

7.7/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N

EPSS Probability

0.21%

10.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-639

References

Timeline

Published: May 11, 2026
Last Modified: Jun 17, 2026
Status: Deferred

Frequently Asked Questions

What is CVE-2026-43890?

Outline is a service that allows for collaborative documentation. From 0.84.0 to 1.7.0, the subscriptions.create API endpoint in server/routes/api/subscriptions/subscriptions.ts exhibits a broken authorization pattern. When both collectionId and documentId are supplied in the request, the route handler authorizes ONLY the collection branch (line 125 if (collectionId)), while the downstream subscriptionCreator command at server/commands/subscriptionCreator.ts writes the subscription against the documentId (which was never validated). The result is a subscription record pinning the attacker's user to a victim document the attacker has no read access to, on any team in the instance. The schema (server/routes/api/subscriptions/schema.ts) only enforces "at least one of collectionId/documentId" via .refine() — it does NOT enforce mutual exclusivity, so passing both is a valid, schema-conforming request. This vulnerability is fixed in 1.7.1.

How severe is CVE-2026-43890?

CVE-2026-43890 has a CVSS score of 7.7/10 (HIGH severity). The EPSS model estimates a 0.21% probability of exploitation in the next 30 days.

How do I fix CVE-2026-43890?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.