10

CVE-2021-28799: QNAP NAS Improper Authorization Vulnerability

CVSS: 10.0v3.1CriticalKEVRansomwareAnalyzed
Published 13-05-2021Last modified 21-10-2025
Open JSON

Vulnerability summary

CVE-2021-28799 is a critical (CVSS 10.0) Improper Authorization vulnerability in QNAP Network Attached Storage (NAS). It is known to be exploited: CISA lists it, first on 31-03-2022. It has been used in ransomware campaigns. EPSS estimates a 78.25% chance of exploitation in the next 30 days, higher than 99.5% of scored vulnerabilities.

Overall risk
90/100
0100
Critical · default modelHow is this calculated?
CVSS score
10.0/10
010
Critical · v3.1 (CVE.org)
EPSS score
78.25%
0%100%
Critical · 0.00 pp in 30 days
KEVListedCISA
RansomwareKnown useFlagged by CISA
Public exploits0No public exploits recorded

Timeline

  1. 13-05-2021
    PublishedVulnerability first disclosed.
  2. 31-03-2022
    Added to CISA KEVQNAP NAS Improper Authorization Vulnerability
  3. 21-04-2022
    CISA remediation dueApply updates per vendor instructions.
  4. 21-10-2025
    Last modifiedVulnerability information updated.

Description

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 .

CVSS metrics

3 scores · 2 sources · 2 versions

EPSS trend

Probability

78.25%

Chance of exploitation in the next 30 days

Percentile

100%

Versus all other CVEs

30-day change

0.00 pp

From 78.25% on 21-09-2026

21-09-202621-10-2026
EPSS score
78.25%

Known exploited

Compare KEV catalogs
CISA KEVListed
Added
31-03-2022
Federal due date
21-04-2022
Ransomware

CISA required action

Apply updates per vendor instructions. nvd.nist.gov/vuln/detail/CVE-2021-28799

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Qnap1 product
Qnap systems inc.1 product
  • hbs 3≥ unspecified, < v16.0.0415 | ≥ unspecified, < v3.0.210412 | ≥ unspecified, < v3.0.210411 | ≥ unspecified, < v16.0.0419

2 vendors · 2 products

References

2 links