How severe is CVE-2021-35030?

CVE-2021-35030 has a CVSS 3.x base score of 3.5, rated low severity. It is exploitable over an adjacent network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability low.

Is CVE-2021-35030 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (17th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-35030?

CVE-2021-35030 primarily affects Zyxel Gs1900-8 Firmware. In total, 12 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-35030?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-35030 published?

CVE-2021-35030 was published on 2021-07-26 and last updated on 2026-06-17.

CVE-2021-35030

CVE-2021-35030 is a low-severity vulnerability in Zyxel Gs1900-8 Firmware with a CVSS 3.x base score of 3.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Low (CVSS 3.x base score 3.5)
CVSS v2: 2.3
EPSS exploit prediction: 0% (17th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Zyxel Gs1900-8 Firmware
Published: 2021-07-26
Last modified: 2026-06-17

Description

A vulnerability was found in the CGI program in Zyxel GS1900-8 firmware version V2.60, that did not properly sterilize packet contents and could allow an authenticated, local user to perform a cross-site scripting (XSS) attack via a crafted LLDP packet.

Frequently asked questions

What is CVE-2021-35030?: A vulnerability was found in the CGI program in Zyxel GS1900-8 firmware version V2.60, that did not properly sterilize packet contents and could allow an authenticated, local user to perform a cross-site scripting (XSS) attack via a crafted LLDP packet.
How severe is CVE-2021-35030?: CVE-2021-35030 has a CVSS 3.x base score of 3.5, rated low severity. It is exploitable over an adjacent network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability low.
Is CVE-2021-35030 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (17th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-35030?: CVE-2021-35030 primarily affects Zyxel Gs1900-8 Firmware. In total, 12 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-35030?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-35030 published?: CVE-2021-35030 was published on 2021-07-26 and last updated on 2026-06-17.

References

https://www.zyxel.com/support/Zyxel_security_advisory_for_XSS_vulnerability_of_GS1900_series_switches.shtml

Affected products (12)

cpe:2.3:o:zyxel:gs1900-8_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-8hp_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-10hp_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-16_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-24e_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-24ep_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-24_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-24hp_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-24hpv2_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-48_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-48hp_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:gs1900-48hpv2_firmware:*:*:*:*:*:*:*:*

More vulnerabilities in Zyxel Gs1900-8 Firmware

CVE-2019-15800 — Critical (CVSS 9.8): An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. Due to lack of input validation in…
CVE-2019-15803 — Critical (CVSS 9.1): An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. Through an undocumented sequence…
CVE-2026-7273 — High (CVSS 8.8): A stack-based buffer overflow vulnerability in the CGI program of Zyxel GS1900-48HPv2 firmware versions…
CVE-2019-15799 — High (CVSS 8.8): An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. User accounts created through the…
CVE-2019-15804 — High (CVSS 7.5): An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. By sending a signal to the CLI…
CVE-2019-15801 — High (CVSS 7.5): An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. The firmware image contains…

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