Auth bypass in Ether Etherpad

CVE-2026-55089

Etherpad is a real-time collaborative editor. From 2.1.0 until 3.1.0, Etherpad's src/node/handler/APIHandler.ts authorizes requests to /api/2/* in the authorization_code OAuth path by using requiredClaims with the admin claim. This check requires only that the claim exists, while src/node/security/OAuth2Provider.ts issues admin: false for configured non-admin users. A non-admin user with a valid signed token can therefore invoke administrative functions including setHTML, setText, appendText, deletePad, copyPad, movePad, restoreRevision, anonymizeAuthor, listAllPads, and listAuthorsOfPad, allowing disclosure, modification, or deletion of pads across the instance. This issue is fixed in version 3.1.0.

Vulnerability class: Broken Access Control

Published · last modified .

CVSS v3 metric

CVSS v3 base score 9.9 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L.

EPSS exploit prediction

EPSS: 0.005 (38.0th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 38th percentile — 38.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-55089: held from 0.004 to 0.005.

EPSS over last 30 days · oldest: 0.004 · newest: 0.005 · change: +0.001

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-55089?
CVE-2026-55089 is a critical-severity vulnerability in Ether Etherpad, classified under Incorrect Authorization. CVSS score: 9.9/10. Published 2026-08-19.
How severe is CVE-2026-55089?
Critical severity. CVSS v3 base score is 9.9 out of 10.