CVE-2021-28799

What it is

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 .

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure, data tampering, service disruption.

In the wild

CISA lists this as exploited in real attacks. Treat as urgent.

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-03-18 00:00 UTC ReservedThe CVE id was reserved by its CNA
2. 2021-05-13 03:15 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2022-03-31 Exploited in the wildAdded to CISA's Known Exploited Vulnerabilities list
4. 2022-04-21 Remediation deadlineCISA's due date for federal agencies to fix it
5. 2026-06-17 03:46 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: yes, CISA lists it. This puts it above everything that is not.
• Exploit odds: 78.2% in the next 30 days (EPSS).
• Severity: 10.0 CRITICAL (CVSS).
• Fix: a patch or advisory is linked.
• It meets the bar for Drop everything: critical, and exploited or very likely to be.

Details

Published

2021-05-13 03:15 UTC

Last modified

2026-06-17 03:46 UTC

Added to CISA KEV

2022-03-31

Exploit probability

78.2% · EPSS, next 30 days

Weakness

CWE-285

Record status

Analyzed

Affected

• Qnap Hybrid Backup Sync < 16.0.0415
• Qnap Hybrid Backup Sync < 3.0.210412
• Qnap Hybrid Backup Sync < 3.0.210411
• Qnap Hybrid Backup Sync < 16.0.0419

Attack profile CVSS 3.1 · 10.0

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-28799.md and follow it. Check whether this project is affected by CVE-2021-28799. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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