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CVE-2021-40344

59
FAUCET Score

CVE-2021-40344 is a critical arbitrary file upload vulnerability affecting Nagios XI version 5.8.5. An authenticated administrator can bypass file extension restrictions in the Custom Includes section by manipulating the MIME type, allowing the upload of malicious PHP scripts. This flaw carries a high CVSS score of 7.2, indicating that an attacker can achieve remote command execution with high impact on confidentiality, integrity, and availability. Despite its severity and high EPSS score, there is currently no public exploit code available, nor is there evidence of active exploitation or significant community discussion.

Impacted Technologies

VendorProductVersion(s)CPE
5.8.5CPE matchmatch criteria
cpe:2.3:a:nagios:nagios_xi:5.8.5:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.2HIGH

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
HIGH
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
1.2
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
66.19%
Probability of exploitation in next 30 days
EPSS Percentile
99.2%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.6619 is in the 99th percentile among its peer group of 5,537 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.3 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

assets.nagios.com / downloads/nagiosxi/CHANGES-5.TXT
Release NotesVendor Advisory
synacktiv.com
Not Applicable
synacktiv.com / sites/default/files/2021-10/Nagios_XI_multiple_vulnerabilities_0.pdf
ExploitThird Party Advisory