Nextcloud Server before 12.0.8 and 13.0.3 suffer from improper authentication on the OAuth2 token endpoint.

published 2018-07-05 8 y ago modified 2026-06-17 4 mo ago also EUVD-2018-15567

cvss: 8.1; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.7%; EPSS 1.7% chance of exploitation in 30 days, percentile 76%
public exploits: 0; none known

Nextcloud Server before 12.0.8 and 13.0.3 suffer from improper authentication on the OAuth2 token endpoint. Missing checks potentially allowed handing out new tokens in case the OAuth2 client was partly compromised.

Patch / fix

fixed in 1

nextcloud nextcloud_server 12.0.8, 13.0.3

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2018-3761 updated 2025-11-21 cvss 6.4

nextcloud: Two flaws fixed in nextcloud 12.0.8

Red Hat All currently supported Red Hat products
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.66% chance of exploitation in the next 30 days, higher than 76% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
NVD	3.1	8.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
NVD	2.0	5.8	AV:N/AC:M/Au:N/C:P/I:P/A:N

Affected products

Nextcloud Nextcloud Server

Classification

Weakness

CWE-287 Improper Authentication

References

nextcloud.com /security/advisory/?id=nc-sa-2018-003
broken-link, vendor-advisory
hackerone.com /reports/343111
third-party-advisory

Sources

CVE List CVE-2018-3761
NVD CVE-2018-3761

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary