CVE-2026-76437

Executive Summary

CVE-2026-76437 is a command injection vulnerability (CWE-78) in the web-based user interface of Cisco License On-Prem (formerly Cisco Smart Software Manager On-Prem / SSM On-Prem). It allows an authenticated remote attacker holding valid administrative credentials to submit crafted configuration content that is improperly validated, resulting in arbitrary command execution on the underlying operating system with root privileges. Because exploitation requires pre-existing administrative access, Cisco characterizes the net privilege gain as limited — the attacker already possesses most administrative capabilities, with the notable exception of the ability to shut down the system, which is the primary impact reflected in the CVSS Availability-only (A:H) scoring.

Technical Analysis

The vulnerability class is OS command injection (CWE-78). Per the NVD description, the root cause is "improper validation of user-supplied content within configurations that are submitted to the web-based management interface." This is a classic pattern in appliance management planes: configuration fields submitted through the web UI are passed to a shell or system call without adequate sanitization, so that shell metacharacters embedded in a configuration value are interpreted by the underlying operating system rather than treated as inert data.

Several points are explicitly stated by the vendor/NVD and should be treated as authoritative:

• Attack surface: the web-based user interface of Cisco License On-Prem, specifically the configuration submission functionality of the web-based management interface.
• Preconditions: the attacker must be authenticated with valid administrative credentials and must be remote (network-reachable).
• Mechanism: crafted configuration content bypasses validation and reaches the OS.
• Result: arbitrary command execution on the underlying operating system with root privileges.
• Net privilege delta: the vendor states the only additional privilege an admin gains is the ability to turn the system off — a capability an administrative user could not normally exercise through the UI alone.

The NVD description does not disclose the specific affected configuration field, parameter name, endpoint, request format, or the exact encoding/character sequence that triggers command execution. No CNA title was supplied and no affected-version list was provided. Accordingly, this report deliberately does not fabricate function names, API paths, or parameter names. Any such specifics found during an engagement must come from the vendor's advisory or independent research, not from this document.

The CVSS vector AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H is internally consistent with the vendor's framing: network reachable, low complexity, high privileges required, no user interaction, no scope change, and Availability-only impact.

Exploitation Scenarios

No public PoC, exploit code, or Nuclei template exists for this CVE. The following attack chain is inferred strictly from the vulnerability class (authenticated OS command injection via configuration input) and the facts stated in the NVD description. Specific implementation details are not available.

1. Reconnaissance / target identification. An attacker identifies a reachable Cisco License On-Prem (SSM On-Prem) web management interface — these appliances are commonly deployed internally, so the attacker is typically an insider, a network-adjacent adversary, or an external actor who has already obtained administrative credentials (e.g., via credential reuse, phishing, or lateral movement). Shodan dorks targeting the appliance's login/management page can corroborate exposure, though internet-facing deployments are expected to be uncommon.

2. Authentication. The attacker authenticates to the web-based management interface using valid administrative credentials. This is a hard precondition: no unauthenticated path is described. The attacker must already hold a privileged account.

3. Triggering the flaw. The attacker navigates to the configuration functionality of the web-based management interface and submits a configuration whose content includes crafted input. Because the application fails to properly validate user-supplied content in submitted configurations, the injected content is not neutralized and is instead interpreted by the underlying operating system. At the vulnerability-class level, this means shell metacharacters embedded in a configuration value are executed by the OS rather than treated as literal data. The NVD description does not disclose which configuration field, request, or character sequence is involved.

4. Post-exploitation impact. Successful exploitation yields arbitrary command execution on the underlying operating system with root privileges. Because the attacker is already an administrator, the incremental gain is limited — the vendor specifically notes the added capability is the ability to turn the system off, which is why Availability is the only affected CVSS metric (A:H) and Confidentiality/Integrity are scored None. That said, root-level OS access is a qualitatively different primitive than a web admin session: it can be leveraged for persistence, pivoting, and tampering that a UI administrator may not normally achieve, and it can be used for denial of service by shutting the system down. Defenders should not dismiss the finding solely because the entry requirement is administrative.

Impact Assessment

• Confidentiality (C:N): No direct confidentiality impact is scored per CVSS; the vendor's framing is that the admin already has system visibility.
• Integrity (I:N): No direct integrity impact is scored; command execution at root could in practice enable tampering, but CVSS scores the stated net gain.
• Availability (A:H): High — the concrete additional capability cited is the ability to shut the system down, which an administrative user cannot normally do. This maps directly to the A:H subscore.

Blast radius. Impact is scoped to individual affected Cisco License On-Prem / SSM On-Prem appliances. In environments where these appliances serve licensing for larger Cisco estates, a shutdown or OS-level compromise can disrupt licensing services and, transitively, the products that depend on them. The CVSS scope is Unchanged (S:U). EPSS is 0.00519 (~42.3rd percentile), indicating low predicted exploitation likelihood relative to the exploited-CVE population — consistent with the high (administrative) precondition. CISA KEV status: Not listed. No exploit-in-the-wild evidence or threat-actor attribution is available.

Detection Guidance

Sigma Rule

title: Cisco License On-Prem Authenticated Command Injection via Configuration Submission
id: 7c9b3a1e-4d2f-4e6a-9b0c-1f2e3d4a5b6c
status: experimental
description: Detects process execution consistent with OS command injection following configuration submission to the Cisco License On-Prem web management interface.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-76437
author: valtersit.com
date: 2026/01/01
logsource:
  category: process_creation
  product: linux
detection:
  selection_parent:
    ParentImage|endswith:
      - '/httpd'
      - '/apache2'
      - '/nginx'
      - '/java'
  selection_commands:
    CommandLine|contains:
      - 'sh -c'
      - 'bash -c'
      - '/bin/sh'
      - '/bin/bash'
      - ';id'
      - '|id'
      - '$(id)'
      - '`id`'
      - ';whoami'
      - ';shutdown'
      - 'shutdown -h'
      - 'shutdown -r'
      - 'reboot'
      - 'poweroff'
  condition: selection_parent and selection_commands
falsepositives:
  - Legitimate maintenance scripts invoked by administrative automation
level: high

YARA Rule

rule CVE_2026_76437_Command_Injection_Config
{
    meta:
        author = "valtersit.com"
        description = "Detects shell metacharacter patterns in Cisco License On-Prem configuration request bodies consistent with command injection attempts"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-76437"
        date = "2026-01-01"

    strings:
        $s1 = "sh -c" ascii nocase
        $s2 = "bash -c" ascii nocase
        $s3 = "/bin/sh" ascii nocase
        $s4 = "/bin/bash" ascii nocase
        $s5 = "$(" ascii
        $s6 = "`id`" ascii
        $s7 = ";id" ascii
        $s8 = ";shutdown" ascii nocase
        $s9 = "poweroff" ascii nocase

    condition:
        uint16(0) == 0x3c25 or 3 of ($s*)
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-76437 Cisco License On-Prem Configuration Command Injection Attempt"; flow:established,to_server; http.method; content:"POST"; http.uri; pcre:"/(config|configuration)/Ui"; http.request_body; content:"sh -c"; nocase; http.request_body; content:"bash -c"; nocase; http.request_body; content:";shutdown"; nocase; threshold: type both, track by_src, count 5, seconds 60; reference:cve,2026-76437; classtype:attempted-admin; sid:202676437; rev:1;)

Note: the http.uri value above is illustrative of a generic configuration endpoint and is not drawn from the NVD description — tune it against observed traffic.

Elastic Detection

process where event.type == "start" and
  process.parent.name in ("httpd", "apache2", "nginx", "java") and
  (
    process.command_line : ("sh -c*", "bash -c*", "/bin/sh*", "/bin/bash*") or
    process.command_line : ("*;id*", "*|id*", "*`id`*", "*$(id)*") or
    process.command_line : ("*shutdown*", "*poweroff*", "*reboot*")
  )

Splunk SPL Query

index=endpoint sourcetype=linux_audit OR sourcetype=sysmon:linux EventType=Process
| where match(lower(parent_process_name), "(httpd|apache2|nginx|java)$")
| where match(lower(command_line), "(sh -c|bash -c|/bin/sh|/bin/bash|;id|\|id|`id`|\$\(id\)|shutdown|poweroff|reboot)")
| stats count values(command_line) as cmds by host, parent_process_name, user
| where count > 0
| sort - count

Wazuh OSSEC Rule

<group name="cisco,web,command_injection,">
  <rule id="100764" level="12">
    <if_sid>5920</if_sid>
    <field name="audit.exe">^/bin/(sh|bash)$</field>
    <regex field="audit.command">(sh -c|bash -c|;id|;shutdown|poweroff|reboot)</regex>
    <description>CVE-2026-76437: Possible OS command injection via Cisco License On-Prem web configuration submission</description>
    <mitre>
      <id>T1190</id>
      <id>T1059</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor fix, workaround, or affected-version list was provided with this CVE record.

1. Immediate mitigations

   • Restrict network access to the Cisco License On-Prem web management interface to trusted management networks only; do not expose it to untrusted or internet-facing segments.
   • Enforce least privilege on administrative accounts and audit all administrator activity; because exploitation requires valid admin credentials, tightening admin access directly reduces exposure.
   • Monitor the appliance and its host OS for unexpected shutdown/poweroff/reboot events and for shell process spawning from web-server parent processes.
   • Apply strict input review to any configuration changes made through the management interface until a fix is available.

2. Patch/upgrade steps

   • No patch reference or fixed version is available in tracked sources. Monitor the Cisco Security Advisories portal for the assigned advisory and the fixed release for Cisco License On-Prem (SSM On-Prem).
   • Treat any fixed version published by Cisco as authoritative and upgrade immediately upon availability.

3. Long-term hardening

   • Architecture: keep licensing management appliances off general-purpose networks and behind strict access control.
   • Application security: ensure configuration input is validated and never passed to an OS shell; use parameterized APIs rather than shell invocation for configuration handling (vendor responsibility).
   • Monitoring: retain the process-execution and configuration-change detections above and alert on anomalies tied to admin sessions.

References

• NVD — CVE-2026-76437: https://nvd.nist.gov/vuln/detail/CVE-2026-76437
• Cisco Security Advisories (vendor portal for Cisco License On-Prem / SSM On-Prem): https://sec.cloudapps.cisco.com/security/center/publicationListing.x
• CWE-78 — Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection'): https://cwe.mitre.org/data/definitions/78.html
• MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
• CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-76437 not listed)

No threat-actor campaigns, public PoC, exploit code, Nuclei templates, or exploit-in-the-wild evidence are associated with this CVE in the data provided.