Security readout for executives and security teams
Plain-English summary
CVE-2021-35027 affects Zyxel ZyWALL VPN2S firmware 1.12(ABLN.0)C0. A remote attacker could use a directory traversal flaw in the device web server to access sensitive information. The sources do not show active exploitation or provide confirmed exploit details.
Executive priority
Treat this as a high-priority confidentiality risk for affected VPN appliances. Prioritize externally reachable devices because the vulnerability requires no credentials or user interaction.
Technical view
The issue is a network-reachable, unauthenticated directory traversal vulnerability in the VPN2S web server. CVSS 3.1 is 7.5, driven by low attack complexity, no privileges, no user interaction, and high confidentiality impact. Integrity and availability impacts are not indicated.
Likely exposure
Exposure is likely limited to Zyxel ZyWALL VPN2S devices running firmware 1.12(ABLN.0)C0, especially where the web server is reachable from untrusted networks.
Exploitation context
The CVE record describes remote sensitive-information access. CISA KEV status is false in the supplied bundle, and no cited source here supports active exploitation.
Researcher notes
Evidence is sparse in the provided bundle. The affected version, vulnerability class, and impact are clear, but patch version, workaround details, exploit maturity, and observed exploitation are not established here.
Mitigation direction
- Inventory ZyWALL VPN2S devices and flag firmware 1.12(ABLN.0)C0 as affected.
- Check Zyxel’s advisory for fixed firmware or vendor-approved mitigation guidance.
- Prioritize vendor-supported remediation for internet-reachable affected devices.
- Monitor Zyxel and CVE records for updated remediation or exploitation information.
Validation and detection
- Verify the exact model and firmware version on each VPN2S device.
- Confirm whether the device web server is reachable from untrusted networks.
- Review web access logs for unusual sensitive-file access indicators.
- Document remediation status against the Zyxel advisory and CVE record.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
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CWE-27: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupFile access behavior lookup
The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-35027 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 7.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N3.93.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://www.zyxel.com/support/Zyxel_security_advisory_for_directory_traversal_and_command_injection_vulnerabilities_of_VPN2S_Firewall.shtmlCVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Path Traversal: 'dir/../../filename'
Path Traversal: 'dir/../../filename' represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.