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Fireware OS EUVDEUVD-2026-67334

| CVE-2026-13086 CRITICAL
Stack-based Buffer Overflow (CWE-121)
2026-08-27 WatchGuard GHSA-c7m7-329m-9vph
9.3
CVSS 4.0 · Vendor: WatchGuard
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Reach Firebox over network
  2. Delivery
    Send crafted request to epm service
  3. Exploit
    Overflow stack buffer (CWE-121)
  4. Execution
    Hijack control flow
  5. Persist
    Execute arbitrary code on appliance
  6. Impact
    Establish perimeter foothold

Vulnerability Assessment

Weakness
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Stack buffer bounds checking
MITRE ATT&CK

1 technique across 1 tactic: Execution

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

Exploitation Conditions

Exploitation requires that the deprecated Mobile Security feature (and its epm / Endpoint Protection Manager service) be present and reachable on the target Fireware OS appliance - that is the concrete gating prerequisite. The CVSS vector (AV:N/AC:L/PR:N/UI:N) confirms no authentication, no user interaction, and low attack complexity, so against an appliance with that service exposed, exploitation is remote and unauthenticated. The primary limiting factor is deployment configuration: appliances that never enabled or have removed the deprecated Mobile Security feature should not expose the vulnerable service, and network segmentation restricting reachability of the epm port further limits practical exposure.

Impact

All strong signals point to high priority: the CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N) describes unauthenticated, low-complexity, network-reachable exploitation with full high impact to confidentiality, integrity, and availability (VC:H/VI:H/VA:H), scoring 9.3. Because the target is a security perimeter device, successful RCE yields a foothold at the network edge - the worst possible location. Countervailing factors temper widespread urgency: no public exploit or POC is identified, the CVE is not in CISA KEV, EPSS is not provided, and the affected service belongs to a deprecated Mobile Security feature, so exposure is limited to appliances still running that configuration rather than the entire Firebox install base. The realistic reading is a critical-but-conditional issue: organizations that never used Mobile Security are likely unaffected, while those that did should patch immediately and treat it as urgent given the appliance's exposure and the absence of authentication.

Exploit ScenarioDerived

An attacker who can reach the Firebox appliance over the network sends a crafted request to the epm service, overflowing a stack buffer to hijack control flow and execute arbitrary code on the appliance with no authentication or user interaction. Because the appliance sits at the network perimeter, this yields an immediate edge foothold for pivoting inward. No public POC is currently identified, so exploitation would require the attacker to develop the overflow independently.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 0.4% exploitation probability (EPSS)

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AnalysisAIv1 – Aug 28, 2026

Remote code execution in WatchGuard Fireware OS affects the epm (Endpoint Protection Manager) service tied to the deprecated Mobile Security feature, where a stack-based buffer overflow lets an unauthenticated remote attacker run arbitrary code on the appliance. The CVSS 4.0 base score is 9.3 (critical) with a network, no-privilege, no-interaction vector. No public exploit identified at time of analysis and it is not listed in CISA KEV, but as a perimeter firewall RCE the impact is severe for any deployment still running Mobile Security.

RemediationAI

Patch available per vendor advisory: apply the fixed Fireware OS release published by WatchGuard in the PSIRT advisory at https://psirt.watchguard.com/CVE-2026-13086 (the input does not include an exact fix version, so confirm the target build in that advisory before upgrading). As a compensating control until patched, disable the deprecated Mobile Security feature so the vulnerable epm service is not active, since it is deprecated this should have minimal operational impact for most deployments. Additionally restrict network reachability of the epm service by blocking or firewalling its listening port from untrusted networks and limiting management/endpoint interfaces to trusted segments; the trade-off is that legitimate Mobile Security clients (if any remain) would lose connectivity, which is acceptable given the feature's deprecated status.

Affected VersionsENISA

Fireware OS 12.0 <12.12.2
Fireware OS 2025.0 <2026.2.2
Fireware OS 12.0 <12.5.20

Affected Packages

euvd fireware_os fix: 12.5.20, 12.12.2, 2026.2.2

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

Fireware OS is the firmware running on WatchGuard Firebox network security appliances (CPE cpe:2.3:a:watchguard:fireware_os). The flaw is CWE-121, a stack-based buffer overflow: attacker-controlled input reaching the epm service overruns a fixed-size stack buffer, corrupting the return address or adjacent stack data and allowing hijack of control flow. The vulnerable code path lives in the Endpoint Protection Manager service associated with the Mobile Security feature, which WatchGuard has marked deprecated - meaning the exposed service may still be present and reachable on appliances that historically enabled or retained that feature.

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  • Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (WatchGuard) PRIMARY 9.3 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
vuln.today AI 9.8 CRITICAL

Unauthenticated network-reachable service (AV:N/PR:N/UI:N) with a low-complexity stack overflow yielding full code execution, so C/I/A all High; scope unchanged.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (WatchGuard).

CVSS VectorVendor: WatchGuard

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Vulnerable system: Confidentiality
High
Vulnerable system: Integrity
High
Vulnerable system: Availability
High
Subsequent system: Confidentiality
None
Subsequent system: Integrity
None
Subsequent system: Availability
None

Lifecycle Timeline

2
Patch available
Aug 28, 2026 - 04:16 EUVD
CVE Published
Aug 27, 2026 - 23:24 cve.org
CRITICAL 9.3

DescriptionCVE.org

A stack-based buffer overflow in the epm (Endpoint Protection Manager) service used by the deprecated Mobile Security feature in WatchGuard Fireware OS allows an unauthenticated remote attacker to execute arbitrary code.

Executive ViewAI

Why It Matters

WatchGuard Fireware OS contains a critical unauthenticated remote code execution vulnerability (CVSS 9.3) in the Mobile Security endpoint protection service, with no vendor patch currently available. Perimeter firewall compromise represents a loss of security boundary controls, potential internal network access, and data exfiltration risk for any organization running this service. Immediate containment and urgent vendor engagement is required.

Business Impact: Severe
Compensating Controls

No vendor-released patch identified at time of analysis. Disable the Mobile Security (epm) feature entirely if not operationally required. Implement strict network-based access controls limiting inbound connections to firewall management interfaces to trusted administrative segments only. Deploy IDS/IPS signatures and behavioral monitoring to detect anomalous epm service activity. Enable comprehensive logging and alerting on firewall telemetry with weekly manual review for indicators of compromise. Maintain isolated, encrypted recovery credentials for incident response.

Threat Intelligence Overview

EPSS Score
0.4%
Top 63% exploitable
Prevalence
Medium
widely used SMB/enterprise firewall vendor, but narrower footprint than Fortinet/Cisco
Social Media
1
Sightings
Data Quality
6 sources
Confidence: High

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity CRITICAL
CISA KEV No
Public POC No
EPSS 0.4%
Patch available Yes
Active threat No
Deciding rule
CRITICAL severity
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision
Out-of-Cycle
Exploitation
None
System Exposure· derived
Open
Automatable
Yes
Human Impact
Very High
Technical Impact
Total

Priority Score

46
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +46
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

A stack-based buffer overflow occurs when a program writes more data to a buffer located on the stack than it was allocated to hold.

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

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