Fireware OS Pre-Authentication Integer Overflow in Access Portal Allows Out-of-Bounds Write (CVE-2026-93866)
Published Last modified Sources: pwn.watch, CVE.org, BSI
What is affected, what to do
An integer overflow vulnerability in the WebSocket connection handling used by WatchGuard Fireware OS's Access Portal allows a remote, unauthenticated attacker to write beyond the bounds of a heap buffer by sending a specially crafted request while the Access Portal feature is enabled.
Update WatchGuard Fireware OS to version 2026.4, WatchGuard Fireware OS to version 12.12.4, WatchGuard Fireware OS to version 12.5.22.
- Affected
- WatchGuard Fireware OS
lt 2025.1..2026.4 - WatchGuard Fireware OS
lt 12.0..12.12.4 - WatchGuard Fireware OS
lt 12.0..12.5.22
- WatchGuard Fireware OS
- Fixed in
- WatchGuard Fireware OS
2026.4 - WatchGuard Fireware OS
12.12.4 - WatchGuard Fireware OS
12.5.22
- WatchGuard Fireware OS
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Metrics
9.2
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: Vendor (CNA), CVSS v4
9.2
CVSS v4
Severity Critical on the scale from 0 to 10.
Source: pwn.watch, CVE.org, BSI
0.4 %
EPSS score
Low — model estimates < 1% exploitation likelihood.
Source: FIRST EPSS, percentile 39.0
Show all metrics
- Severity
- Critical
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 88.17 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- no public PoC known
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 9.2 Methodology
CVSS v4
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 9.2
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 0.4 %
- Low — model estimates < 1% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 39.0
- High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- —
- Published
CWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-190, CWE-288, CWE-787
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
An integer overflow vulnerability in the WebSocket connection handling used by WatchGuard Fireware OS's Access Portal allows a remote, unauthenticated attacker to write beyond the bounds of a heap buffer by sending a specially crafted request while the Access Portal feature is enabled.
Source: pwn.watch, NVD (NIST), cvelistv5, BSI CSAF, BSI WID Portal
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| WatchGuard | Fireware OS |
|
|
| WatchGuard | Fireware OS Mobile VPN with SSL Client |
|
|
Vendors and products
Weakness classes (CWE)
CWE-190Integer Overflow or Wraparound
Base
The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
Entry at MITRE CWE-190CWE-288Authentication Bypass Using an Alternate Path or Channel
Base
The product requires authentication, but the product has an alternate path or channel that does not require authentication.
Entry at MITRE CWE-288CWE-787Out-of-bounds Write
Base
The product writes data past the end, or before the beginning, of the intended buffer.
Entry at MITRE CWE-787
References & sources
- psirt.watchguard.comCVE-2026-93866Vendor advisory
- pwn.watchpwn.watch: WatchGuard Fireware OS 2026.4 and 12.12.4 fix 17 Firebox flaws, including unauthenticated bugs in the SIP proxy, Access Portal and FireClusterpwn-watch
- psirt.watchguard.comWatchGuard Security Advisories (Oct 27 2026 batch)pwn-watch
- psirt.watchguard.comCVE-2026-93857: Fireware OS Pre-Authentication Stack Buffer Overflow in SIP Proxy Allows Remote Code Executionpwn-watch
- psirt.watchguard.comCVE-2026-93866: Fireware OS Pre-Authentication Integer Overflow in Access Portal Allows Out-of-Bounds Writepwn-watch
- psirt.watchguard.comCVE-2026-93865: Fireware OS Missing Authentication in FireCluster Sync Daemon Allows Remote Root Action Injectionpwn-watch
- psirt.watchguard.comCVE-2026-112710: Fireware OS Heap Buffer Overflow in AD Authentication Service Allows Pre-Authentication Remote Code Executionpwn-watch
- psirt.watchguard.comCVE-2026-103594: Fireware OS Stack Buffer Overflow in WireGuard Configuration Allows Remote Code Executionpwn-watch
- psirt.watchguard.comCVE-2026-103593: Fireware OS Stack Buffer Overflow in Logging Service Allows Remote Code Executionpwn-watch
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
ReceivedWatchGuard
CVSS V4.0: AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Weakness type: CWE-787, CWE-190, CWE-288
Description added or changed
New references:Show 7 original changes
Individual changes of this event as published by NVD Type Action Before After Description added —An integer overflow vulnerability in the WebSocket connection handling used by WatchGuard Fireware OS's Access Portal allows a remote, unauthenticated attacker to write beyond the bounds of a heap buffer by sending a specially crafted request while the Access Portal feature is enabled.CVSS added —AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:XWeakness type (CWE) added —CWE-787Weakness type (CWE) added —CWE-190Weakness type (CWE) added —CWE-288Affected versions (publisher) added —New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/93xxx/CVE-2026-93866.json">CVE-2026-93866</a>Reference added —https://psirt.watchguard.com/CVE-2026-93866Source identifier: 5d1c2695-1a31-4499-88ae-e847036fd7e3
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<a href="https://intel.neosec.eu/en/cve/CVE-2026-93866"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-93866.svg?lang=en" alt="CVE-2026-93866 – NEOSEC Intel" height="20"></a>