CVE-2026-48554

Executive Summary

CVE-2026-48554 is an authenticated remote code execution vulnerability in Nagios Core (before 4.5.14) and Nagios XI (before 2026R1.7). The flaw arises from unfiltered macro substitution in NOTIFICATION-family macros ($NOTIFICATIONCOMMENT$, $NOTIFICATIONAUTHOR$) processed via the com_data parameter, which can reach shell-executed contexts in notification commands. Successful exploitation allows an authenticated UI user to execute arbitrary operating system commands as the nagios service account, requiring a non-default configuration where notification commands invoke these macros in shell command lines. The vulnerability carries a CVSS score of 7.5, reflecting high confidentiality, integrity, and availability impact, though attack complexity is high and a low-privilege account is required.

Technical Analysis

The vulnerability resides in how Nagios processes notification-related macros and substitutes them into notification command strings. Specifically, the macros $NOTIFICATIONCOMMENT$ and $NOTIFICATIONAUTHOR$ are inserted into command templates that are subsequently executed by the shell. The untrusted data flows through the com_data parameter of the notification subsystem, which is accessible via the authenticated UI (e.g., when a user acknowledges an alert, adds a comment, or configures notification attributes).

The root cause is a CWE-78 (Improper Neutralization of Special Elements used in an OS Command), indicating that macro-expanded content is placed into a command line without adequate sanitization, metacharacter escaping, or proper use of shell-array invocation semantics. Because notification commands are typically executed by the Nagios core process (or its CGI/worker subprocesses), which run under the nagios user account, any injection vector via macro expansion yields command execution with that privilege level.

The attack surface is the Nagios web interface (UI): any authenticated user capable of triggering a notification event and supplying input that populates $NOTIFICATIONCOMMENT$ or $NOTIFICATIONAUTHOR$ can embed shell metacharacters (;, |, $(), backticks, etc.) into the command string. The shell interprets these metacharacters when the notification command is executed. The "non-default configuration" requirement means that the default Nagios installation does not reference these two macros in shell-executed notification commands; however, many deployments (custom notification scripts, email handlers, or enterprise-integration wrappers) commonly include these macros to add context to alerts, making such deployments susceptible.

Because the vector requires that a notification command explicitly references these macros in a shell-reachable position, the vulnerability is conditional rather than unconditional: the default installation is effectively safe, but a broader set of custom configurations is exposed. This is consistent with the high attack complexity score in the CVSS vector.

Exploitation Scenarios

I. Reconnaissance / Target Identification

1. An attacker identifies a Nagios Core or Nagios XI instance exposed on the internet (e.g., via Shodan query for "title:Nagios" or "Nagios XI"). The attacker enumerates the version to confirm it is below 4.5.14 (Core) or 2026R1.7 (XI).
2. The attacker determines whether the target has a non-default notification configuration that references $NOTIFICATIONCOMMENT$ or $NOTIFICATIONAUTHOR$ in a shell-executed command. This can be inferred from publicly available configuration templates or by probing behavior (e.g., injecting benign test characters and observing email/script output).

II. Authentication and Trigger 3. The attacker authenticates to the UI with a valid low-privileged account (e.g., a monitoring user or an operator role). No administrative privileges are required per the CVSS vector (PR:L). 4. The attacker crafts a malicious comment or author string containing shell payloads — for example, content that includes a command substitution pattern such as $(command) or a semicolon followed by an OS command. The payload is submitted through the notification/comment interface, populating the com_data parameter destined for the $NOTIFICATIONCOMMENT$ or $NOTIFICATIONAUTHOR$ macro.

III. Execution 5. When the associated notification event fires (e.g., a service goes critical and the notification command runs), the shell executes the notification command line with the attacker-supplied macro content substituted. Because the content is unfiltered before being passed to the shell, the embedded commands are executed as the nagios user.

IV. Post-Exploitation 6. The attacker gains arbitrary command execution in the context of the nagios account, which typically has read access to Nagios configuration files (potentially containing credentials for monitored hosts or database connection strings). Depending on the underlying OS hardening and Nagios service permissions, the attacker may escalate to root via misconfigured SUID binaries or leveraged services, then pivot laterally into the monitored infrastructure.

No public PoC or exploit code is confirmed available; the attack chain above is inferred strictly from the vulnerability class (CWE-78 OS command injection) and the described mechanism in the NVD description. Specific implementation details beyond the mentioned macros and parameter are insufficient in the public data.

Impact Assessment

CVSS Breakdown (derived from vector CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H):

• Attack Vector: Network — exploitable from any reachable network position.
• Attack Complexity: High — successful exploitation requires a non-default configuration and specific macro usage in notification commands, increasing the practical difficulty.
• Privileges Required: Low — a standard authenticated UI user can trigger the flaw.
• User Interaction: None — no victim interaction required beyond normal notification processing.
• Scope: Unchanged — the compromised component (Nagios core process) is the same trust boundary.
• Confidentiality/Integrity/Availability: High — arbitrary command execution as the nagios user permits data exfiltration, configuration tampering, and full service disruption.

Business Impact: Nagios is a central monitoring platform that provides visibility into the health of infrastructure. Compromise of the Nagios server grants an attacker:

• Read access to host/service definitions, which often contain credentials (SNMP community strings, database DSNs, API tokens) used for monitoring.
• Ability to disable or modify monitoring rules, effectively blinding the organization to ongoing incidents.
• Potential pivot point into monitored systems, as the nagios user often maintains SSH keys or agent credentials for remote checks.

Affected Systems: All Nagios Core versions prior to 4.5.14 and Nagios XI versions prior to 2026R1.7 with custom notification commands referencing the vulnerable macros. Default installations are likely not exposed, but the broad usage of custom notification scripts in enterprise environments significantly expands the realistic attack surface.

Blast Radius: The immediate blast radius is the host running Nagios. Given Nagios's central role in network/infrastructure monitoring, lateral movement to monitored assets is a realistic post-exploitation chain, amplifying the severity beyond the single host compromise.

Detection Guidance

Sigma Rule

title: Nagios NOTIFICATION Macro Command Injection Attempt
id: 3f7a9c2e-9d41-4c6b-bb8e-1a2f4c7d8e9f
status: experimental
description: Detects attempts to exploit CVE-2026-48554 via shell metacharacters in Nagios notification macro parameters
author: ValtersIT Threat Intel Team
date: 2026/02/15
logsource:
    category: webserver
    product: apache
    service: accesslog
detection:
    selection:
        c-uri|contains:
            - 'cmd=acknowledge'
            - 'com_data='
        c-uri|contains|any:
            - '%3B'
            - '%7C'
            - '%24%28'
            - '%60'
            - '%0A'
        c-uri|contains:
            - 'NOTIFICATIONCOMMENT'
            - 'NOTIFICATIONAUTHOR'
    condition: selection
level: high
falsepositives:
    - Legitimate use of special characters in monitoring comments (rare)
tags:
    - attack.t1210
    - attack.execution
    - cve.2026.48554

YARA Rule

rule Nagios_CVE_2026_48554_Command_Injection
{
    meta:
        author = "ValtersIT Threat Intel Team"
        date = "2026-02-15"
        description = "Detects payload patterns targeting Nagios notification macro substitution"
        cve = "CVE-2026-48554"
        severity = "high"
    strings:
        $macro1 = "$NOTIFICATIONCOMMENT$"
        $macro2 = "$NOTIFICATIONAUTHOR$"
        $param = "com_data="
        $semi = ";"
        $pipes = "|"
        $cmd_sub = "$("
        $backtick = "`"
    condition:
        ($param at 0 or filesize < 50KB) and
        (1 of ($macro*)) and
        (1 of ($semi, $pipes, $cmd_sub, $backtick))
}

Suricata IDS Rule

alert http any any -> any any (msg:"NAGIOS CVE-2026-48554 Notification Macro Command Injection Attempt"; flow:established,to_server; content:"com_data="; http_uri; nocase; content:"NOTIFICATIONCOMMENT"; http_uri; nocase; pcre:"/(%3B|%7C|%24|%60|;|\||\$\(|`)/i"; classtype:attempted-admin; sid:20264855401; rev:1; metadata:created_at 2026_02_15, updated_at 2026_02_15, cve CVE-2026-48554;)

Elastic Detection

sequence by source.ip, user.name with maxspan=5m
  [network where destination.port == 443 and process.name : "httpd*" and
   wildcard(request.uri, "*com_data=*") and
   (request.uri contains "NOTIFICATIONCOMMENT" or
    request.uri contains "NOTIFICATIONAUTHOR")]
  [file where process.name : "nagios*" and
   (file.name like "*cmd*" or file.name like "*notify*") and
   event.action == "exec"]

Splunk SPL Query

index=web sourcetype=access_combined
| where like(uri_path, "%com_data=%") 
  AND (like(uri_path, "%NOTIFICATIONCOMMENT%") OR like(uri_path, "%NOTIFICATIONAUTHOR%"))
  AND (like(uri_path, "%3B%") OR like(uri_path, "%7C%") OR like(uri_path, "%24%") OR like(uri_path, "%60%"))
| stats count by src_ip, user, uri_path, _time
| sort - _time

Wazuh OSSEC Rule

<group name="nagios,">
  <rule id="225905" level="12">
    <decoded_as>json</decoded_as>
    <field name="url">\.com_data=</field>
    <field name="url">NOTIFICATIONCOMMENT|NOTIFICATIONAUTHOR</field>
    <regex>%3B|%7C|%24\(|%60|\;|\||\$\(|`</regex>
    <description>Nagios CVE-2026-48554 command injection attempt via notification macro</description>
    <mitre>
      <id>T1210</id>
    </mitre>
    <group>attack_execution,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Status: The vulnerability is confirmed as UNPATCHED (patch confidence 0/4). No evidence of a vendor fix has been observed from any tracked source at the time of this report. The NVD description references fixed versions (Nagios Core 4.5.14, Nagios XI 2026R1.7), but no official advisory or patch distribution has been confirmed.

Immediate Mitigations (no vendor patch):

1. Audit all Nagios notification command definitions. Identify any command that references $NOTIFICATIONCOMMENT$ or $NOTIFICATIONAUTHOR$ and is executed via /bin/sh, exec, or a wrapper script that invokes a shell. Replace such macros with sanitized alternatives or remove them entirely.
2. If these macros are required for business operations, wrap shell execution in a wrapper script that escapes shell metacharacters before passing the macro content (e.g., printf '%q' in bash, or escapeshellarg-equivalent logic).
3. Restrict UI access: enforce multi-factor authentication, limit the set of users who can acknowledge alerts/comments, and apply network-level access control (allowlist source IPs) to the Nagios web interface.
4. Run Nagios under a container or restricted JVM/user with minimal privileges; revoke the nagios user's write access to its own configuration and restrict any sudo capabilities.
5. Monitor web access logs and shell process execution for anomalies (as per the detection rules above).

Patch/Upgrade Steps (once available):

1. Monitor vendor channels (nagios.org, GitHub advisories) for official patches or updated builds for Nagios Core 4.5.14 and Nagios XI 2026R1.7.
2. Test the upgrade in a staging environment with identical notification command configurations before production rollout.
3. Apply the upgrade; verify notification commands that previously used the vulnerable macros continue to function without requiring shell metacharacter stripping.

Long-Term Hardening:

1. Establish a policy that all Nagios notification integrations must be implemented using a non-shell execution path (e.g., direct function calls, piped stdin, or parameterized subprocess APIs) rather than concatenating macro content into shell command lines.
2. Implement configuration validation that rejects any notification command line containing macro references in shell-sensitive positions (i.e., not quoted or escaped).
3. Integrate Nagios configuration files into version control with automated security scanning for shell-metacharacter usage patterns adjacent to macros.
4. Segment the Nagios server from the broader network to limit lateral movement if compromised, and enforce least-privilege access for the nagios service account at the OS level.

References

1. NVD Entry — https://nvd.nist.gov/vuln/detail/CVE-2026-48554
2. MITRE CVE Record — https://www.cve.org/CVERecord?id=CVE-2026-48554
3. CWE-78 Reference — https://cwe.mitre.org/data/definitions/78.html (Improper Neutralization of Special Elements used in an OS Command)
4. Nagios Official Site / Advisories — https://www.nagios.org/ (monitor for pending security advisory referencing CVE-2026-48554)
5. AT&T&CK T1210 — https://attack.mitre.org/techniques/T1210/ (Exploitation of Remote Services)

CISA KEV: No entry. Threat Actor Activity: No known campaigns or exploit-in-the-wild evidence reported at the time of writing. PoC Status: Unknown — no confirmed public proof-of-concept has been verified; Nuclei template and exploit code are both absent.