Threats / QNAP / CVE-2021-28799
CVE-2021-28799
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
QNAP Network Attached Storage (NAS) vulnerability
QNAP NAS devices running HBS 3 contain an improper authorization flaw allowing remote attackers to gain unauthorized login access without valid credentials.
Verdict
Today item, not a backlog item.
A remote authentication bypass in QNAP NAS HBS 3 enables unauthenticated access. The high EPSS score and active exploitation in ransomware campaigns indicate immediate risk to unpatched storage infrastructure.
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
137 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-03-31), flagged for known ransomware use.
Probability (EPSS)
EPSS 0.78395 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: QNAP, Network Attached Storage (NAS). Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-285 Improper Authorization — weakness family: Authorization / access control.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I identify a QNAP NAS device running HBS 3 exposed to the network and exploit the authorization bypass to gain remote login access without credentials.
Business
Attackers obtain direct administrative control of network-attached storage containing critical business data and backups.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
Once authenticated, I enumerate stored data, disable backup functions, and establish persistence for follow-on attacks.
Business
Backup systems are compromised, eliminating recovery options and increasing ransomware campaign success rates.
3
Lateral reach — past segmentation narrative 3
Attacker
I deploy ransomware payloads across the NAS and connected network resources, encrypting data at scale.
Business
Operations halt as critical data becomes inaccessible; ransom demands follow with threat of data sale or destruction.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05
Coverage & confidence
— what we know, and what we don’tEstablished (cited)
Coverage gaps — stated, not hidden
Disclosure & credit2
Catalogued by qnapCNA
Credited with finding itZUSO ARTunspecified