How severe is CVE-2021-21820?

CVE-2021-21820 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-2021-21820 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (86th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-21820?

CVE-2021-21820 affects Dlink Dir-3040 Firmware. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-21820?

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-2021-21820 published?

CVE-2021-21820 was published on 2021-07-16 and last updated on 2026-06-17.

CVE-2021-21820

CVE-2021-21820 is a critical-severity vulnerability in Dlink Dir-3040 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-798.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 3% (86th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-798
Affected product: Dlink Dir-3040 Firmware
Published: 2021-07-16
Last modified: 2026-06-17

Description

A hard-coded password vulnerability exists in the Libcli Test Environment functionality of D-LINK DIR-3040 1.13B03. A specially crafted network request can lead to code execution. An attacker can send a sequence of requests to trigger this vulnerability.

Frequently asked questions

What is CVE-2021-21820?: A hard-coded password vulnerability exists in the Libcli Test Environment functionality of D-LINK DIR-3040 1.13B03. A specially crafted network request can lead to code execution. An attacker can send a sequence of requests to trigger this vulnerability.
How severe is CVE-2021-21820?: CVE-2021-21820 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-2021-21820 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (86th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21820?: CVE-2021-21820 affects Dlink Dir-3040 Firmware. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-21820?: 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-2021-21820 published?: CVE-2021-21820 was published on 2021-07-16 and last updated on 2026-06-17.

References

https://talosintelligence.com/vulnerability_reports/TALOS-2021-1285

Affected products (1)

cpe:2.3:o:dlink:dir-3040_firmware:1.13b03:*:*:*:*:*:*:*

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