How severe is CVE-2021-40344?

CVE-2021-40344 has a CVSS 3.x base score of 7.2, rated high severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-40344 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 66% (99th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-40344?

CVE-2021-40344 affects Nagios Nagios Xi. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-40344?

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

When was CVE-2021-40344 published?

CVE-2021-40344 was published on 2021-10-26 and last updated on 2026-06-17.

CVE-2021-40344

CVE-2021-40344 is a high-severity vulnerability in Nagios Nagios Xi with a CVSS 3.x base score of 7.2. Its EPSS exploit-prediction score of 66% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-434.

Key facts

Severity: High (CVSS 3.x base score 7.2)
CVSS v2: 6.5
EPSS exploit prediction: 66% (99th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-434
Affected product: Nagios Nagios Xi
Published: 2021-10-26
Last modified: 2026-06-17

Description

An issue was discovered in Nagios XI 5.8.5. In the Custom Includes section of the Admin panel, an administrator can upload files with arbitrary extensions as long as the MIME type corresponds to an image. Therefore it is possible to upload a crafted PHP script to achieve remote command execution.

Frequently asked questions

What is CVE-2021-40344?: An issue was discovered in Nagios XI 5.8.5. In the Custom Includes section of the Admin panel, an administrator can upload files with arbitrary extensions as long as the MIME type corresponds to an image. Therefore it is possible to upload a crafted PHP script to achieve remote command execution.
How severe is CVE-2021-40344?: CVE-2021-40344 has a CVSS 3.x base score of 7.2, rated high severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-40344 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 66% (99th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-40344?: CVE-2021-40344 affects Nagios Nagios Xi. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-40344?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-40344 published?: CVE-2021-40344 was published on 2021-10-26 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:nagios:nagios_xi:5.8.5:*:*:*:*:*:*:*

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