Threats / QNAP / CVE-2021-28799
CVE-2021-28799
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
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.
CISA KEV Yes · 2022-03-315Ransomware use Flagged5EPSS 0.7825 (verify live)6CVSS 103CISA SSVC Exploitation: active · Automatable: yes · Impact: total4Exploit Public PoC / detection · nuclei template12
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
169 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 0.7825 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 10 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H) · Affected: QNAP, Network Attached Storage (NAS). Confirm exact fixed builds in the vendor advisory.CVSS — CNA-assigned (CVE.org), version 3.1, set at disclosure.
Weakness (CWE)
Mapped to CWE-285 Improper Authorization — weakness family: Authorization / access control.CWE — CNA-assigned (CVE.org); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: yes · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 322 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
Public exploit available
Public exploit tooling is catalogued for this CVE (a public proof-of-concept / detection template). Catalog entries: nuclei template. We link the catalog page(s) only — no payload or code is hosted or restated here.Link, never host — the catalog page is the source; basicsecurity.net does not redistribute payloads.
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