What is CVE-2021-28799?

CVE-2021-28799 is a critical-severity vulnerability in QNAP Hybrid Backup Sync, classified under Improper Authorization. CVSS score: 10.0/10. Published 2021-05-13.

How severe is CVE-2021-28799?

Critical severity. CVSS v3 base score is 10.0 out of 10.

Is CVE-2021-28799 known to be exploited?

Yes. CVE-2021-28799 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-03-31), indicating it is being actively exploited. 4 public proof-of-concept repositories are indexed.

Auth bypass in QNAP Hybrid Backup Sync

CVE-2021-28799

An improper authorization vulnerability has been reported to affect QNAP NAS running HBS 3 (Hybrid Backup Sync. ) If exploited, the vulnerability allows remote attackers to log in to a device. This issue affects: QNAP Systems Inc. HBS 3 versions prior to v16.0.0415 on QTS 4.5.2; versions prior to v3.0.210412 on QTS 4.3.6; versions prior to v3.0.210411 on QTS 4.3.4; versions prior to v3.0.210411 on QTS 4.3.3; versions prior to v16.0.0419 on QuTS hero h4.5.1; versions prior to v16.0.0419 on QuTScloud c4.5.1~c4.5.4. This issue does not affect: QNAP Systems Inc. HBS 2 . QNAP Systems Inc. HBS 1.3 .

EPSS: 0.782 (99.5th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 10.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H.

Affected products

Qnap Hybrid_backup_sync
Qnap Qts — versions 4.5.2, 4.3.6, 4.3.3
Qnap Qutscloud
Qnap Quts_hero — versions h4.5.1
Qnap Systems Inc. Hbs 1.3 — versions all versions
Qnap Systems Inc. Hbs 2 — versions all versions
Qnap Systems Inc. Hbs 3 — versions unspecified

Weakness classification (CWE)

CWE-285 — Improper Authorization

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2022-03-31. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2022-04-21.

Required action: Apply updates per vendor instructions.

Known ransomware campaign use: yes.

Public proof-of-concept exploits

References

security@qnapsecurity.com.tw (x_refsource_MISC, Vendor Advisory)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)

Frequently asked questions

What is CVE-2021-28799?: CVE-2021-28799 is a critical-severity vulnerability in QNAP Hybrid Backup Sync, classified under Improper Authorization. CVSS score: 10.0/10. Published 2021-05-13.
How severe is CVE-2021-28799?: Critical severity. CVSS v3 base score is 10.0 out of 10.
Is CVE-2021-28799 known to be exploited?: Yes. CVE-2021-28799 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-03-31), indicating it is being actively exploited. 4 public proof-of-concept repositories are indexed.