How severe is CVE-2020-24355?

CVE-2020-24355 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2020-24355 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-24355?

CVE-2020-24355 affects Zyxel Vmg5313-b30b Firmware. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2020-24355?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2020-24355 published?

CVE-2020-24355 was published on 2020-09-02 and last updated on 2026-06-17.

CVE-2020-24355

CVE-2020-24355 is a critical-severity vulnerability in Zyxel Vmg5313-b30b Firmware with a CVSS 3.x base score of 9.8. 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-732.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 10.0
EPSS exploit prediction: 2% (80th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-732
Affected product: Zyxel Vmg5313-b30b Firmware
Published: 2020-09-02
Last modified: 2026-06-17

Description

Zyxel VMG5313-B30B router on firmware 5.13(ABCJ.6)b3_1127, and possibly older versions of firmware are affected by insecure permissions which allows regular and other users to create new users with elevated privileges. This is done by changing "FirstIndex" field in JSON that is POST-ed during account creation. Similar may also be possible with account deletion.

Frequently asked questions

What is CVE-2020-24355?: Zyxel VMG5313-B30B router on firmware 5.13(ABCJ.6)b3_1127, and possibly older versions of firmware are affected by insecure permissions which allows regular and other users to create new users with elevated privileges. This is done by changing "FirstIndex" field in JSON that is POST-ed during account creation. Similar may also be possible with account deletion.
How severe is CVE-2020-24355?: CVE-2020-24355 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2020-24355 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-24355?: CVE-2020-24355 affects Zyxel Vmg5313-b30b Firmware. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2020-24355?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2020-24355 published?: CVE-2020-24355 was published on 2020-09-02 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:o:zyxel:vmg5313-b30b_firmware:*:*:*:*:*:*:*:*

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