What is the CVSS score of CVE-2026-43890?

CVE-2026-43890 has a CVSS 3.1 base score of 7.7 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N. EPSS exploitation probability: 0.0%.

Which versions of Outline are affected by CVE-2026-43890?

Outline self-hosted documentation platform versions 0.84.0 through 1.7.0 contain an authorization bypass vulnerability; publicly available exploit code exists.. A patch is available.

How to fix or mitigate CVE-2026-43890?

Within 24 hours, identify all Outline deployments and their versions by auditing infrastructure records and contacting teams managing instances. Within 7 days, apply the vendor patch to all affected instances running versions 0.84.0 through 1.7.0 per the vendor advisory. Within 30 days, audit subscription records and access logs for unauthorized document subscriptions and revoke any inappropriate permissions identified.

Outline CVE-2026-43890

EUVD-2026-29334 HIGH

Authorization Bypass Through User-Controlled Key (CWE-639)

2026-05-11 GitHub_M

Authentication Bypass Outline

7.7

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

7.7 HIGH

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

vuln.today AI

5.0 MEDIUM

Network-reachable, low-complexity, authenticated (PR:L) cross-tenant break gives S:C; impact assessed C:L rather than C:H since a subscription leaks update/notification signals, not full document reads, matching SSVC 'partial'.

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

4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Changed

Confidentiality

High

Integrity

None

Availability

None

Lifecycle Timeline

Analysis Generated

Jul 23, 2026 - 23:33 vuln.today

Patch available

May 11, 2026 - 23:03 EUVD

CVE Published

May 11, 2026 - 21:09 nvd

HIGH 7.7

DescriptionGitHub Advisory

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.

AnalysisAI

Broken object-level authorization in Outline (self-hosted collaborative documentation) versions 0.84.0 through 1.7.0 lets an authenticated user subscribe to any document across any team, including documents they have no read access to. The subscriptions.create API validates only the collection branch when both collectionId and documentId are submitted, but the subscriptionCreator command writes the record against the unvalidated documentId. Publicly available exploit path is described in the vendor advisory (SSVC 'poc'); EPSS is very low at 0.03% (8th percentile), indicating no observed mass exploitation.

Technical ContextAI

Outline is a Node/TypeScript knowledge-base and wiki application supporting multi-team (multi-tenant) deployments. The flaw is CWE-639 (Authorization Bypass Through User-Controlled Key / IDOR): in server/routes/api/subscriptions/subscriptions.ts the handler branches on 'if (collectionId)' (line 125) and performs the authorization check only against the collection, while the downstream command at server/commands/subscriptionCreator.ts persists the subscription keyed to documentId. The Zod schema in schema.ts uses .refine() to require 'at least one of collectionId/documentId' but does NOT enforce mutual exclusivity, so a request carrying both fields is fully schema-conforming. The attacker therefore satisfies the authorized collection check with a collection they legitimately access while smuggling in an arbitrary victim documentId that is never authorized.

RemediationAI

Upgrade to Outline 1.7.1, which corrects the authorization logic (Vendor-released patch: 1.7.1); this is the primary and recommended fix per the advisory at https://github.com/outline/outline/security/advisories/GHSA-gf8h-cv9v-q4fw. If an immediate upgrade is not possible, restrict or proxy the /api/subscriptions.create endpoint to reject requests that supply both collectionId and documentId simultaneously via a reverse-proxy or WAF rule, since legitimate clients typically send only one; the trade-off is potential breakage if any internal tooling relies on sending both. Because exploitation requires an authenticated account, additionally tighten account provisioning and audit subscription records for entries pinning users to documents outside their accessible collections, then revoke anomalous subscriptions until patched.