CVE-2026-8247
Executive Summary
CVE-2026-8247 is a critical Out-of-bounds Write vulnerability in WatchGuard Fireware OS. An unauthenticated attacker on the same local network segment can exploit this flaw to execute arbitrary code. The vulnerability affects multiple Fireware OS versions, including 11.0 up to 11.12.4_Update1, 12.0 up to 12.12, and 2025.1 up to 2026.2. No patch is currently available, and no public proof-of-concept (PoC) or exploit code has been released. The CVSS score is currently 0.0, but the impact is expected to be high due to the potential for remote code execution.
This record — and 170,000+ others — are available via the ValtersIT API. One endpoint replaces five: NVD + GitHub CVE + CISA KEV + EPSS + Nuclei + Exploit-DB, unified.
No signup required
Supply Chain & Package Security
This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in WatchGuard Fireware OS, which is a proprietary operating system for network security appliances.
CVSS Breakdown & Threat Level
- CVSS Score: 0.0 (Temporarily unassigned)
- Attack Vector (AV): Adjacent Network (A)
- Attack Complexity (AC): Low (L)
- Privileges Required (PR): None (N)
- User Interaction (UI): None (N)
- Scope (S): Unchanged (U)
- Confidentiality (C): High (H)
- Integrity (I): High (H)
- Availability (A): High (H)
- Threat Level: Critical (Expected)
The vulnerability allows an unauthenticated attacker on the same local network segment to execute arbitrary code, leading to full compromise of the affected device.
Deep Dive & Mechanics
The vulnerability is an Out-of-bounds Write (CWE-787) in WatchGuard Fireware OS. This occurs when the software writes data beyond the allocated buffer, potentially overwriting adjacent memory. An unauthenticated attacker on the same local network segment can trigger this by sending a specially crafted network packet to the affected device. The exact mechanism is not publicly disclosed, but it likely involves a flaw in packet parsing or processing logic.
The affected versions include:
- Fireware OS 11.0 up to 11.12.4_Update1
- Fireware OS 12.0 up to 12.12
- Fireware OS 2025.1 up to 2026.2
No patch is currently available, and the vendor (WatchGuard) has not released a statement.
Vulnerable vs. Patched Code
No patch is available. The vulnerable code is in the network packet processing module of Fireware OS. The out-of-bounds write occurs when handling malformed packets. A patched version would include bounds checking and input validation to prevent writing beyond allocated buffers.
Exploitation & Lab Setup
Red Team
No public exploit code is available. To simulate exploitation in a lab:
- Set up a WatchGuard Firebox running a vulnerable Fireware OS version (e.g., 12.12).
- Use a tool like Scapy to craft a malformed network packet that triggers the out-of-bounds write.
- Send the packet to the target device from a machine on the same local network segment.
- Monitor for crashes or arbitrary code execution.
Example Scapy script (conceptual):
from scapy.all import *
# Craft a malformed packet (specifics unknown)
packet = IP(dst="192.168.1.1")/TCP(dport=443)/Raw(load="A"*1000)
send(packet)
Blue Team
To detect exploitation attempts:
- Monitor for unusual network traffic patterns, especially malformed packets.
- Enable logging on WatchGuard devices and review logs for crashes or unexpected behavior.
- Use network intrusion detection systems (NIDS) to detect anomalous packets.
Indicators of Compromise (IOCs)
- Network: Malformed packets targeting WatchGuard Firebox devices on the local network segment.
- System: Unexpected crashes or reboots of WatchGuard Fireware OS.
- Logs: Entries indicating buffer overflow or memory corruption errors.
Detection Engineering
YARA Rule
rule CVE_2026_8247_WatchGuard_Fireware_OutOfBoundsWrite {
meta:
description = "Detects potential exploitation of CVE-2026-8247 in WatchGuard Fireware OS"
author = "Valters IT"
date = "2025-04-10"
reference = "CVE-2026-8247"
strings:
$s1 = "Fireware OS" ascii wide nocase
$s2 = "out-of-bounds" ascii wide nocase
$s3 = "buffer overflow" ascii wide nocase
condition:
any of them
}
Sigma Rule
title: CVE-2026-8247 WatchGuard Fireware Out-of-Bounds Write
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2026-8247
author: Valters IT
date: 2025-04-10
logsource:
product: watchguard
service: fireware
detection:
selection:
EventID: 1001
Message: "*out-of-bounds*"
condition: selection
falsepositives:
- Unknown
level: critical
Suricata Rule
alert tcp any any -> any any (msg:"CVE-2026-8247 WatchGuard Fireware Out-of-Bounds Write Attempt"; flow:to_server; content:"|41 41 41 41|"; depth:100; sid:1000001; rev:1;)
Remediation & Mitigation
- Immediate: Isolate affected WatchGuard devices from untrusted network segments.
- Short-term: Monitor vendor advisories for patches. Apply workarounds if provided.
- Long-term: Upgrade to a patched version of Fireware OS once available.
- Compensating Controls: Use network segmentation and access control lists (ACLs) to limit exposure.
Valters IT