CVE-2021-28799
CVE-2021-28799 is a security flaw in QNAP Network Attached Storage (NAS), a network drive for storing files and backups at home or in a small office. Attackers are using a flaw in QNAP Network Attached Storage (NAS). The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 31 Mar 2022, and says ransomware gangs have used it.[1]
QNAP Network Attached Storage (NAS) is in things households have: network drives for files and backups, so the fix matters at home as much as at work. Fixed in version v16.0.0415, v3.0.210412, v3.0.210411 and v16.0.0419 of HBS 3.
Description
CISA calls it an NAS improper authorization in QNAP Network Attached Storage (NAS). In its words: “QNAP NAS running HBS 3 contains an improper authorization vulnerability which can allow remote attackers to log in to a device.”[1]
The CVE record adds: “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 .”[2]
The underlying weakness is CWE-285, in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| HBS 3 | v16.0.0415 |
| HBS 3 | v3.0.210412 |
| HBS 3 | v3.0.210411 |
| HBS 3 | v16.0.0419 |
Every device with QNAP Network Attached Storage (NAS) needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 31 Mar 2022, 322 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 21 Apr 2022 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 78%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
QNAP has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Update QNAP Network Attached Storage (NAS) now.Install the latest update from QNAP on every device that has it, and restart when asked. Then turn on automatic updates, so the next fix arrives on its own.
- Check you’re on v16.0.0415 or later.Fixed in version v16.0.0415, v3.0.210412, v3.0.210411 and v16.0.0419 of HBS 3. Anything older is what attackers are going after.
- If the maker has stopped updating it, replace it.Network drives stop getting fixes after a few years, and attackers keep a list of the ones that did. If there’s no newer firmware, it won’t be fixed.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 78%.[4] |
See also
Other QNAP Network Attached Storage (NAS) flaws
- CVE-2018-19953: NAS file station cross-site scripting ·
- CVE-2018-19949: NAS file station command injection ·
- CVE-2018-19943: NAS file station cross-site scripting ·
Other QNAP flaws
- CVE-2023-47565, QNAP VioStor NVR: OS command injection ·
- CVE-2022-27593, QNAP Photo Station: externally controlled reference ·
- CVE-2019-7195, QNAP Photo Station: path traversal ·
- CVE-2019-7194, QNAP Photo Station: path traversal ·
- CVE-2019-7193, QNAP QTS: improper input validation ·
Similar flaws
- CVE-2018-13382, Fortinet FortiOS and FortiProxy: improper authorization ·
- CVE-2021-1675, Microsoft Windows: print spooler remote code execution ·
Added the same day
- CVE-2022-26871, Trend Micro Apex Central: arbitrary file upload ·
- CVE-2022-1040, Sophos Firewall: authentication bypass ·
- CVE-2021-34484, Microsoft Windows: user profile service privilege escalation ·
- CVE-2021-21551, Dell dbutil Driver: insufficient access control ·
- CVE-2018-10562, Dasan Gigabit Passive Optical Network (GPON) Routers: GPON routers command injection ·
Every QNAP flaw on CISA’s list · Everything added in March 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “QNAP NAS Improper Authorization Vulnerability”. Known Exploited Vulnerabilities Catalog, added 31 Mar 2022.
- ^ National Institute of Standards and Technology. “CVE-2021-28799 Detail”. National Vulnerability Database, published 13 May 2021.
- ^ QNAP. Advisories and fixes: qnap.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.782, percentile 99.6, 31 Oct 2026.
- CVE Program. “CVE-2021-28799”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.