Security Resilience

CVE-2021-20123

Path Traversal in Draytek Vigorconnect 1.6.0

CISA KEVActive ExploitationEUVD ExploitedPublic PoCPath Traversal
Published
13 October 2021
Modified
03 November 2025
KEV Added
03 September 2024
CVSS Score v3.1 7.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS Score 0.90 99.8th percentile
Risk Priority 84 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2021-20123 is a high-severity Path Traversal (CWE-22) vulnerability in Draytek Vigorconnect. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Data Obfuscation (T1001); ranked in the top 0.2% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2021-20123 is a path traversal vulnerability, tracked as CWE-22, that affects Draytek VigorConnect version 1.6.0-B3. The flaw exists in the DownloadFileServlet endpoint used for file downloads and permits access to arbitrary files on the underlying operating system.

An unauthenticated remote attacker can exploit the issue over the network without any user interaction or credentials. Successful exploitation grants the ability to read arbitrary files with root privileges, producing a high confidentiality impact consistent with the assigned CVSS 3.1 score of 7.5.

The vulnerability appears in CISA's Known Exploited Vulnerabilities catalog and is detailed in Tenable research advisory TRA-2021-42, confirming that mitigation should follow vendor guidance for upgrading or restricting access to the affected endpoint.

OWASP Top 10 for Web (2025)

A01:2025 Broken Access Control

EU & UK References

Vulnerability Data

A local file inclusion vulnerability exists in Draytek VigorConnect 1.6.0-B3 in the file download functionality of the DownloadFileServlet endpoint. An unauthenticated attacker could leverage this vulnerability to download arbitrary files from the underlying operating system with root privileges.

CWE(s)
CWE-22
KEV Date Added
03 September 2024

Related Threats

MITRE ATT&CK Enterprise Techniques

T1001 Data Obfuscation Command And Control
Adversaries may obfuscate command and control traffic to make it more difficult to detect.
attack.mitre.org →
T1003.003 NTDS Credential Access
Adversaries may attempt to access or create a copy of the Active Directory domain database in order to steal credential information, as well as obtain other information about domain members such as devices, users, and access rights.
attack.mitre.org →
T1003.004 LSA Secrets Credential Access
Adversaries with SYSTEM access to a host may attempt to access Local Security Authority (LSA) secrets, which can contain a variety of different credential materials, such as credentials for service accounts.
attack.mitre.org →
T1003.006 DCSync Credential Access
Adversaries may attempt to access credentials and other sensitive information by abusing a Windows Domain Controller's application programming interface (API)(Citation: Microsoft DRSR Dec 2017) (Citation: Microsoft GetNCCChanges) (Citati…
attack.mitre.org →
T1016.001 Internet Connection Discovery Discovery
Adversaries may check for Internet connectivity on compromised systems.
attack.mitre.org →
T1018 Remote System Discovery Discovery
Adversaries may attempt to get a listing of other systems by IP address, hostname, or other logical identifier on a network that may be used for Lateral Movement from the current system.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2021-20124Same product: Draytek Vigorconnectboth on KEV
CVE-2023-1009Same vendor: Draytek
CVE-2023-1163Same vendor: Draytek
CVE-2023-6265Same vendor: Draytek
CVE-2024-23721Same vendor: Draytek
CVE-2024-1708Shared CWE-22both on KEV
CVE-2022-41328Shared CWE-22both on KEV
CVE-2015-0016Shared CWE-22both on KEV
CVE-2021-41773Shared CWE-22both on KEV
CVE-2024-57727Shared CWE-22both on KEV

Affected Assets

draytek
vigorconnect
1.6.0

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V5.3.2

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

SI-10 Information Input Validation
addresses: CWE-22

Validates pathnames and filenames to prevent traversal outside intended directories.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-02 partial match
blocks

Patching/maintenance can remediate known path-traversal flaws in deployed software (partial prevention of exploitability) but does nothing to stop the coding defect from being introduced in the first place.

PR.AA-05 none match
blocks

PR.AA-05 defines and reviews access policies but does not address code-level pathname neutralization, so neither direction prevents CWE-22.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.14 Information transfer partial match
removes
A.5.15 Access control partial match
removes
A.5.16 Identity management partial match
removes
A.5.17 Authentication information partial match
removes
A.5.18 Access rights partial match
removes
A.8.10 Information deletion partial match
removes

References