THREATPORT/VULNERABILITY/CVE-2021-28809
CRITICAL SEVERITY

CVE-2021-28809

Hybrid Backup Sync vulnerability

CVSS
9.8
EPSS
15.8%
EPSS pct
97th
Exploited
No known
An improper access control vulnerability has been reported to affect certain legacy versions of HBS 3. If exploited, this vulnerability allows attackers to compromise the security of the operating system.QNAP have already fixed this vulnerability in the following versions of HBS 3: QTS 4.3.6: HBS 3 v3.0.210507 and later QTS 4.3.4: HBS 3 v3.0.210506 and later QTS 4.3.3: HBS 3 v3.0.210506 and later
Affected vendor
Qnap
Affected product
Hybrid Backup Sync
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness type (CWE)
  • CWE-284 — Improper Access Control
  • CWE-306 — Missing Authentication for Critical Function
  • CWE-749 — Exposed Dangerous Method or Function
Published
2021-07-08

Risk analysis

Based on its CVSS vector, this vulnerability is exploitable over the network, low attack complexity, requiring no privileges, no user interaction. Successful exploitation leads to high impact to confidentiality, high impact to integrity, high impact to availability.

Its EPSS score of 15.8% reflects a moderate probability of exploitation activity in the wild over the next 30 days, placing it above 97% of all scored CVEs.

Check your external exposure to CVE-2021-28809

  • Confirm whether Qnap Hybrid Backup Sync is running on any internet-facing host or subdomain.
  • Match discovered service fingerprints against the version affected by CVE-2021-28809.
  • Prioritise remediation if the asset is public, business-critical, or near authentication/payment flows.

How ThreatPort helps with CVE-2021-28809

ThreatPort's external attack surface scanner checks your internet-facing assets — agentlessly, from the outside in — for the exposed services and versions that CVE-2021-28809 affects, then prioritises the finding by real risk using CISA KEV and FIRST.org EPSS.

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