CVE-2026-86104

Executive Summary

CVE-2026-86104 is an uncontrolled resource consumption (CWE-400) vulnerability in the Fireware OS login process — specifically the wgagent component — that allows a remote, unauthenticated attacker to trigger a denial of service by sending a specially crafted request. Any internet-facing or network-reachable device running an affected Fireware OS build is in scope, and successful exploitation degrades or halts the login/authentication service. Impact is availability-only: an attacker can disrupt administrative and authentication access to the appliance without any credential or prior foothold.

Technical Analysis

The vulnerability resides in the Fireware OS login process implemented by the wgagent component. Per the NVD description, the flaw is an uncontrolled resource consumption condition (CWE-400). In this class of bug, the software fails to adequately bound the resources (memory, CPU, file descriptors, session slots, process threads, etc.) that a single request or request stream can consume. When an attacker submits a specially crafted request to the login process, the process allocates or holds resources without effective limits, which can result in exhaustion of those resources and a denial of service for legitimate users.

Key properties derivable from the supplied data:

• Attack vector: Remote and network-reachable (AV:N).
• Authentication: None required (PR:N), meaning the attacker does not need valid credentials to reach the vulnerable code path.
• User interaction: None (UI:N).
• Impact: Availability-only (C:N, I:N, A:H); no confidentiality or integrity impact is described.
• ATT&CK mapping: T1499 (Endpoint Denial of Service) — the attacker degrades or prevents access to a service by exhausting its resources.

Because the description does not disclose the precise request format, parameter names, or internal function calls in wgagent, no specific payload structure, endpoint path, or code-level allocation site can be asserted. What can be stated at the vulnerability-class level is that the login process does not enforce an effective resource ceiling on attacker-controlled input, so a crafted request drives disproportionate consumption relative to normal authentication traffic. The exact resource (memory vs. CPU vs. session handlers) is not specified in the source data and should not be assumed.

The wgagent login service is part of the management/authentication surface of Fireware OS. That surface is typically reachable from the management network and, in misconfigured or deliberately exposed deployments, from untrusted networks — which is what raises the practical severity of an unauthenticated resource-exhaustion bug to that of a network-facing DoS primitive.

Exploitation Scenarios

The attack chain below is described strictly at the vulnerability-class level; no public PoC exists and no implementation-specific details are invented.

1. Reconnaissance / target identification. An attacker identifies a reachable Fireware OS management/login surface exposing wgagent. Internet-exposed or management-VLAN-reachable appliances are the natural targets. Asset discovery can be performed via Shodan queries (see METADATA) and standard service banners. Because no authentication is required, the attacker does not need to obtain or crack credentials.

2. Triggering the flaw class. The attacker sends a specially crafted request to the login process. Per the CWE-400 classification, the crafted request causes the login process to consume resources without an effective bound. The attacker repeats or scales the request to drive resource consumption past the point at which the service can continue to serve legitimate login attempts. No specific parameter, path, or byte sequence is asserted here because none is provided in the source data.

3. Payload / execution method (class level). This is a resource-exhaustion attack, not remote code execution. The "payload" is the crafted request itself — its effect is to monopolize an unbounded resource in the wgagent login process. The attack requires only network reachability; it does not require memory-corruption primitives, deserialization gadgets, or any code execution technique.

4. Post-exploitation impact. Successful exploitation results in a denial of service to the login process. Administrative users may be unable to authenticate to the appliance, and authentication-dependent functionality can become unavailable. The description does not indicate data exfiltration, configuration tampering, or persistence, so those outcomes should not be assumed. Sustained or repeated requests can extend the outage.

Note: No public PoC is available; the attack chain above is inferred from the CWE-400 vulnerability class and the stated characteristics (remote, unauthenticated, availability-only).

Impact Assessment

• Confidentiality: None (C:N) per the vector — no data exposure is described.
• Integrity: None (I:N) — no modification of data or configuration is described.
• Availability: High (A:H) — the login process can be rendered unavailable to legitimate users.
• Privileges required: None (PR:N) — unauthenticated.
• User interaction: None (UI:N).
• Scope: Unchanged (S:U) — impact is confined to the vulnerable component.

Business impact. Fireware OS login/authentication is a control-plane function. If it is unavailable, administrators cannot authenticate to manage the appliance, and any security or access functions gated on that login path are affected. For an edge security appliance, loss of the management login path can translate into operational loss of visibility and control over the perimeter — a serious condition during an active incident or change window. Because the bug is availability-only and unauthenticated, an attacker can use it to create a persistent or repeated operational disruption with minimal effort and no footprint on data integrity. Blast radius is bounded to the appliance itself and the services that depend on its login/authentication path; it is not described as spreading laterally. The CVSS base score is recorded as N/A in the supplied data and is not asserted here; the vector expressed above should be treated as the qualitative characterization of severity.

Detection Guidance

Detection is complicated by the absence of published request specifics. The rules below detect the class of activity — anomalous request volume or malformed/oversized requests against the Fireware login/wgagent process, plus process-level resource exhaustion — and should be tuned against a known-good baseline.

Sigma Rule

title: Potential CVE-2026-86104 Fireware OS Login Process Resource Exhaustion
id: 3f7c1a2e-9b84-4d1a-8e6f-1c0d2ab5e7f1
status: experimental
description: Detects anomalous request volume or resource pressure against the Fireware OS login process (wgagent), consistent with CWE-400 exploitation.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-86104
author: valtersit.com
date: 2026/01/01
tags:
  - attack.t1499
logsource:
  product: firewall
  service: auth
detection:
  selection:
    process|contains: 'wgagent'
  resource_pressure:
    - cpu_usage|gte: 90
    - memory_usage|gte: 90
  selection_login:
    Message|contains:
      - 'login'
      - 'authentication'
  condition: selection and (resource_pressure or selection_login)
falsepositives:
  - Legitimate authentication spikes during maintenance or bulk admin sessions
  - Backup/polling systems interacting with the management interface
level: medium

YARA Rule

rule CVE_2026_86104_Fireware_Wgagent_Resource_Exhaustion_Artifacts
{
    meta:
        description = "Detects artifacts/log messages indicating resource exhaustion in the Fireware OS wgagent login process (CWE-400)"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-86104"
        date = "2026-01-01"
        severity = "medium"

    strings:
        $svc   = "wgagent" ascii wide nocase
        $login = "login" ascii wide nocase
        $auth  = "authentication" ascii wide nocase
        $r1    = "out of memory" ascii wide nocase
        $r2    = "resource exhausted" ascii wide nocase
        $r3    = "too many" ascii wide nocase
        $r4    = "cannot allocate" ascii wide nocase

    condition:
        filesize < 2MB and
        $svc and
        ( $login or $auth ) and
        any of ($r*)
}

Suricata IDS Rule

alert tcp any any -> $HOME_NET any ( \
  msg:"CVE-2026-86104 Possible Fireware OS wgagent Login Resource Exhaustion Attempt"; \
  flow:to_server,established; \
  content:"wgagent"; nocase; \
  http_header; \
  threshold:type both, track by_src, count 100, seconds 30; \
  classtype:attempted-dos; \
  reference:url,nvd.nist.gov/vuln/detail/CVE-2026-86104; \
  sid:202686104; rev:1; )

Elastic Detection

sequence by source.ip with maxspan=30s
  [ network where network.protocol == "tcp" and
      process.name : "wgagent" and
      url.path : "*login*" ]
  [ network where network.protocol == "tcp" and
      process.name : "wgagent" and
      message : ("authentication" or "login") ]

Splunk SPL Query

index=firewall OR index=system sourcetype=watchguard:*
(process="wgagent" OR host=*fw*)
(Message="*login*" OR Message="*authentication*" OR Message="*resource*")
| bin _time span=1m
| stats count AS attempts, dc(src_ip) AS unique_sources BY host, src_ip, _time
| where attempts > 75 OR unique_sources > 5
| sort - attempts

Wazuh OSSEC Rule

<group name="fireware,cve-2026-86104,">
  <rule id="202686104" level="10" frequency="6" timeframe="120">
    <if_matched_sid>202686100</if_matched_sid>
    <match>wgagent</match>
    <description>CVE-2026-86104 - Multiple resource-exhaustion login attempts against Fireware OS wgagent from $(srcip)</description>
    <group>dos,pci_dss_10.2.4,gdpr_IV_35.7.d,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED — no patch evidence from any tracked source; no vendor fix or affected-version list is available in the supplied data.

1) Immediate mitigations

• Restrict management access to the Fireware OS login/wgagent surface. Do not expose the management interface to the public internet or untrusted networks; enforce access from a dedicated management VLAN.
• Apply network-layer allowlists and firewall rules so only authorized administrative hosts can reach the login/authentication service.
• Enable rate-limiting and connection-flood protections on the perimeter facing the appliance so a single source cannot generate unbounded request volume.
• Enable detailed logging/alerting on the login service and monitor for sustained spikes in resource usage or authentication failures.
• Maintain out-of-band access to the appliance so it can be recovered if the login process is exhausted.

2) Patch / upgrade steps

• No fixed version is identified in the supplied data. Monitor the vendor's security advisory channel for Fireware OS updates addressing CVE-2026-86104 and apply updates per vendor guidance once released.
• Until a fix is available, treat the appliance as unpatched and lean on the network-level mitigations above.

3) Long-term hardening

• Minimize the exposed attack surface of all security appliances; keep management interfaces private by default.
• Deploy continuous monitoring and anomaly detection for the login process, with baselines for request volume and resource consumption.
• Integrate CVE feeds and vendor advisories into a patch-management workflow so security-appliance firmware receives priority patching.
• Validate mitigations through periodic resilience/DoS testing against staging appliances.

References

• NVD — CVE-2026-86104: https://nvd.nist.gov/vuln/detail/CVE-2026-86104
• CWE-400 — Uncontrolled Resource Consumption: https://cwe.mitre.org/data/definitions/400.html
• MITRE ATT&CK T1499 — Endpoint Denial of Service: https://attack.mitre.org/techniques/T1499/
• WatchGuard Security Advisories (vendor advisory portal — monitor for the CVE-specific advisory and fixed Fireware OS release): https://www.watchguard.com/wgrd-psirt/advisories
• CISA Known Exploited Vulnerabilities Catalog (CVE-2026-86104 was NOT listed as KEV at the time of writing; no exploit-in-the-wild or threat-actor campaign evidence is available in the supplied data): https://www.cisa.gov/known-exploited-vulnerabilities-catalog