Security readout for executives and security teams
Plain-English summary
CVE-2021-35030 is a low-severity XSS issue in Zyxel GS1900-8 firmware 2.60. An authenticated local user could use crafted LLDP packet content to affect the switch's CGI interface. Business urgency is limited unless this exact switch firmware is present in trusted internal networks.
Executive priority
Treat as routine remediation unless the affected switch is in a sensitive internal segment or local account compromise is plausible. Prioritize inventory confirmation first, then follow Zyxel guidance if firmware 2.60 is found.
Technical view
The issue is CWE-79 in a CGI program that did not properly sanitize packet contents. The CVSS 3.1 score is 3.5 with adjacent attack vector, low complexity, high privileges, no user interaction, and limited integrity and availability impact. The source bundle identifies Zyxel GS1900-8 firmware version 2.60 as affected.
Likely exposure
Exposure appears limited to environments running Zyxel GS1900-8 firmware version 2.60. The CVSS vector indicates adjacent network access and high privileges are required. The provided sources do not identify broader affected models or versions.
Exploitation context
The source bundle does not report active exploitation, and CISA KEV status is false. The described path requires an authenticated local user and crafted LLDP packet content, making this more relevant to insider, compromised local account, or segmented-network scenarios than internet-scale exposure.
Researcher notes
Evidence is narrow: the bundle names GS1900-8 firmware 2.60, CWE-79, and a CGI sanitization failure involving LLDP packet contents. Do not assume other GS1900 series devices are affected without vendor confirmation. No exploit status or fixed version is included in the supplied bundle.
Mitigation direction
- Inventory Zyxel GS1900-8 switches and record firmware versions.
- If version 2.60 is present, review Zyxel advisory for vendor-fixed firmware guidance.
- Restrict administrative access to trusted management networks and accounts.
- Limit local network access to switch management and LLDP-adjacent segments where feasible.
Validation and detection
- Confirm whether any Zyxel GS1900-8 device runs firmware version 2.60.
- Review switch management access controls for local authenticated users.
- Check whether LLDP is enabled in relevant network segments.
- Review logs for unusual authenticated switch-management activity.
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
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. 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 lookupCVE-2021-35030 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Low
- CVSS
- 3.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:A/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L
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:A/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L0.92.5Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
3.5LowVector: CVSS:3.1/AV:A/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L
Source materials
- CVE List V5 sourceCVE List V5
- https://www.zyxel.com/support/Zyxel_security_advisory_for_XSS_vulnerability_of_GS1900_series_switches.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.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.