CVE-2026-21891
Auth bypass in ZimaOS login: common service usernames bypass password check; any password grants access.
Is CVE-2026-21891 being exploited?
Not confirmed. CVE-2026-21891 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 2.4% probability of exploitation in the next 30 days.
How severe is CVE-2026-21891?
CVE-2026-21891 is rated Critical with a CVSS score of 9.4. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-21891?
Yes. A fix has been recorded for CVE-2026-21891. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-21891 affect?
CVE-2026-21891 affects ZimaOS <= 1.5.0, CasaOS-based devices on x86-64 with UEFI. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-21891?
Disable/restrict service usernames; enable MFA; monitor login attempts; plan patch.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Authentication bypass: if login username matches a service account, any password allows access.
Immediate action required
- affected<= 1.5.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.