Zulip Authentication Backend Configuration Bypass

published 2025-04-16 18 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-11790

cvss: 8.2; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.4%; EPSS 0.4% chance of exploitation in 30 days, percentile 30%
public exploits: 0; none known

Zulip is an open-source team collaboration tool. Zulip supports a configuration where account creation is limited solely by being able to authenticate with a single-sign on authentication backend, meaning the organization places no restrictions on email address domains or invitations being required to join, but has disabled the EmailAuthBackend that is used for email/password authentication. A bug in the Zulip server means that it is possible to create an account in such organizations, without having an account with the configured SSO authentication backend. This issue is patched in version 10.2. A workaround includes requiring invitations to join the organization prevents the vulnerability from being accessed.

Patch / fix

fixed in 2 links 1

zulip zulip 10.2
zulip zulip_server 10.2

github.com/zulip/zulip@b5ab90a commit

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: partial
Assessed: 18 mo ago (2025-04-17)

Exploit prediction

0.36% chance of exploitation in the next 30 days, higher than 30% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	8.2	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

Affected products

zulip zulip

Classification

Weakness

CWE-287 Improper Authentication

References

Sources

CVE List CVE-2025-31478
NVD CVE-2025-31478

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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.

Summary