CVE-2021-25299 — Nagios Xi
MEDIUMCVE-2021-25299 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in nagios nagios xi. 2 public exploit references exist, so weaponization risk is real. No vendor fix is recorded yet; mitigation options are listed below.
Nagios XI version xi-5.7.5 is affected by cross-site scripting (XSS). The vulnerability exists in the file /usr/local/nagiosxi/html/admin/sshterm.php due to improper sanitization of…
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-25299 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,333 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Description
Nagios XI version xi-5.7.5 is affected by cross-site scripting (XSS). The vulnerability exists in the file /usr/local/nagiosxi/html/admin/sshterm.php due to improper sanitization of user-controlled input. A maliciously crafted URL, when clicked by an admin user, can be used to steal his/her session cookies or it can be chained with the previous bugs to get one-click remote command execution (RCE) on the Nagios XI server.
Affected Products
nagios xinagiosResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Vendor / applianceDetect
Inventory every nagios nagios xi deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for remote code execution at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
Remediation status
No patch has shipped for CVE-2021-25299 yet — track the nagios nagios xi advisory for a fixed release and apply the workarounds below in the meantime.
Mitigate without a patch
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2021-25299 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.
Tailored to CVE-2021-25299. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
How to detect CVE-2021-25299
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2021-25299 -u https://target- Template
- Nagios XI 5.7.5 - Cross-Site Scripting
- Severity
- medium
- Impact
- Attackers can craft malicious URLs containing JavaScript that executes when clicked by admin users, potentially stealing session cookies that can be chained with other vulnerabilities for one-click remote command execution and complete Nagios XI server compromise.
- Remediation
- Upgrade Nagios XI to the latest version or apply the provided patch to fix the XSS vulnerability.
Template by ProjectDiscovery nuclei-templates (ritikchaddha), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2021-25299 being exploited in your environment?
O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2021-25299 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.