CVE-2026-5188 - Integer underflow in X.509 SAN parsing in wolfSSL

ANALYST: BIVASH KUMAR NAYAK (CHIEF SECURITY ARCHITECT) • PUBLISHED: Friday, 10 April 2026

TLP:CLEAR // CDB-GOC CVE INTELLIGENCE ADVISORY // SENTINEL APEX v30.0

Report ID: CDB-CVE-2026-0410-0B82AA | Classification: TLP:CLEAR | Published: 2026-04-10 06:06:06 UTC

Prepared By: CyberDudeBivash Global Operations Center (GOC) | Report Type: CVE Intelligence Advisory - NVD-Verified | Distribution: SOC / Enterprise / Executive

TLP:CLEAR CVSS N/A [OK] NVD-VERIFIED [!] PATCH STATUS UNKNOWN [!] Vulnerability Disclosure

CYBERDUDEBIVASH SENTINEL APEX(TM) // CVE THREAT INTELLIGENCE ADVISORY

CVE-2026-5188: An integer underflow issue exists in wolfSSL when parsing the Subject Alternative Name (SAN) extension of X

NVD-Verified Intelligence Advisory - CyberDudeBivash Sentinel APEX(TM) | All technical claims verified against NIST NVD, CERT/CC, and official vendor references.

1. EXECUTIVE SUMMARY

[OK] VERIFIED INTELLIGENCE

CVE-2026-5188 is a -severity vulnerability published on April 10, 2026 with a CVSS base score of N/A. The vulnerability is classified under CWE-191 (Weakness Classification CWE-191).

Vulnerability Summary (NVD-Verified)

An integer underflow issue exists in wolfSSL when parsing the Subject Alternative Name (SAN) extension of X.509 certificates. A malformed certificate can specify an entry length larger than the enclosing sequence, causing the internal length counter to wrap during parsing. This results in incorrect handling of certificate data. The issue is limited to configurations using the original ASN.1 parsing implementation which is off by default.

Key Metrics at a Glance

Attribute	Value	Source
CVE ID	CVE-2026-5188	NIST NVD
CVSS Base Score	N/A ()	NVD CVSS
Weakness Class	CWE-191	NVD / MITRE CWE
NVD Status	Received	NIST NVD
Published	April 10, 2026	NIST NVD
Last Modified	April 10, 2026	NIST NVD
Intelligence Confidence	Medium - NVD entry received, awaiting full analysis. Consult vendor advisory for confirmation.	CDB-GOC Assessment

Business Risk Implications: Organizations running locally accessible the affected software deployments are at risk. An attacker can exploit this vulnerability with low-privilege credentials. This unknown-severity vulnerability in the affected software requires immediate remediation. Apply vendor patch within your scheduled maintenance window. Consult the vendor advisory in Section 9 for affected versions and patch instructions.

2. VULNERABILITY OVERVIEW

CVSS Vector Analysis

CVSS Vector:

Metric	Interpretation

Weakness Classification

[OK] MITRE CWE / NVD VERIFIED

CWE ID	Name	Class
CWE-191	Weakness Classification CWE-191	Software Weakness

CWE-191 - Technical Context

This vulnerability is classified under CWE-191 by NVD/MITRE. Security teams should consult the MITRE CWE database for complete technical details on this weakness class.

OWASP Category: Refer to OWASP Top 10 for applicable category

3. VERIFIED TECHNICAL DETAILS

[OK] NVD AUTHORITATIVE DESCRIPTION

NVD Official Description:

Source: NIST National Vulnerability Database | Status: Received | Last Modified: April 10, 2026

Affected Products and Versions

[OK] NVD DESCRIPTION DERIVED

Affected versions are described in the official NVD entry: CVE-2026-5188. Consult the NVD reference and vendor advisory links in Section 9 for the authoritative affected version list.

From NVD description: An integer underflow issue exists in wolfSSL when parsing the Subject Alternative Name (SAN) extension of X.509 certificates. A malformed certificate can specify an entry length larger than the enclosing sequence, causing the internal length counter to wrap during parsing. This results in incorrect ...

Vulnerability Mechanism (From Verified Description)

The following technical analysis is derived exclusively from the NVD description, associated CWE classification (CWE-191), and CVSS vector (). No additional attack scenarios have been extrapolated beyond the verified vulnerability scope.

CVSS Exploitability Profile

[OK] NVD CVSS VERIFIED

Parameter	Value
Base Score	None ()
Exploitability Score	N/A/3.9
Impact Score	N/A/5.9
CVSS Vector String

[!] Scope Boundary: The technical analysis above is confined to the verified vulnerability scope as disclosed in the NVD entry. Claims regarding malware, firmware compromise, process injection, credential interception, OTP theft, supply chain attacks, or any attack technique not directly described in the NVD entry are outside the verified scope of this vulnerability and are not asserted in this report.

4. RESEARCHER ATTRIBUTION

Researcher attribution data is not available in the NVD entry for CVE-2026-5188 at the time of this report's generation. CYBERDUDEBIVASH Sentinel APEX(TM) will update this section if attribution information becomes available via NVD, CERT/CC, or researcher public disclosure.

5. SECURITY IMPLICATIONS

[i] SECURITY IMPLICATIONS - Derived from Verified Facts

The following implications follow logically from the verified vulnerability facts. These represent the realistic security consequences of the vulnerability as disclosed. They are not extrapolated attack scenarios.

Direct Security Consequences

Weakness Classification CWE-191: This vulnerability is classified under CWE-191 by NVD/MITRE. Security teams should consult the MITRE CWE database for complete technical details on th

Attack Surface Assessment

Affected Population

Based on the verified technical scope, the following user populations are affected:

Organizations running affected versions of the software described in the NVD entry
Users or administrators with access to the affected component or endpoint
Systems where the affected software is internet-facing or accessible by untrusted users

Consult the NVD entry and vendor advisory for the definitive list of affected versions. Systems that have applied the vendor patch or mitigation are not affected.

6. THREAT INTELLIGENCE CONTEXT

[!] THREAT INTELLIGENCE HYPOTHESIS - Analytical Speculation

The scenarios below are analytical hypotheses derived from the vulnerability class, CVSS characteristics, and threat landscape context. They are not confirmed exploitation reports. They represent plausible - but unverified - threat scenarios that security teams may wish to consider in their risk modeling.

Potential Abuse Scenario: Based on the CVSS vector and CWE classification, threat actors aware of this vulnerability may attempt exploitation in targeted attack chains. Organizations should monitor for indicators consistent with the exploitation techniques described in the MITRE ATT&CK mapping in the Detection section.

These scenarios are analytical hypotheses based on the vulnerability class and CVSS characteristics. No active exploitation campaigns have been confirmed in public reporting at the time of this advisory.

Note: The vulnerability itself does not directly implement malware functionality. However, similar technical weaknesses can sometimes contribute to broader attack chains when combined with other techniques. Any such scenarios are speculative and clearly labeled as hypotheses in this advisory.

7. DETECTION OPPORTUNITIES

Detection strategies should be tailored to the vulnerability class (CWE-191). Consult the MITRE ATT&CK techniques in the table below for specific detection opportunities aligned to the threat model.

MITRE ATT&CK Technique Mapping (CWE-Verified)

No direct MITRE ATT&CK mapping established for this CWE combination. Consult the NVD entry for additional context.

Sigma Rule (SIEM-Agnostic)

Deploy to Microsoft Sentinel, Splunk, Elastic, or any Sigma-compatible platform. Rule scope is aligned to the actual vulnerability class, not a generic campaign template.

title: Vulnerability Exploitation Attempt - CVE-2026-5188
id: cdb-cve_2026_5188-sigma-001
status: experimental
description: >
  Monitors for indicators consistent with exploitation of CVE-2026-5188.
  An integer underflow issue exists in wolfSSL when parsing the Subject Alternative Name (SAN) extension of X.509 certific...
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-5188
author: CyberDudeBivash Sentinel APEX(TM) GOC
date: 2026/04/10
tags:
  - attack.initial_access
  - attack.t1190
  - cve.cve_2026_5188
logsource:
  category: application
detection:
  keywords:
    - 'CVE-2026-5188'
  condition: keywords
falsepositives:
  - Vulnerability scanner activity
  - Security research tools
level: medium

YARA Rule (Endpoint / Binary Analysis)

Scoped to the vulnerability class (CWE-191). Apply to application binaries and memory forensics relevant to the affected component.

/*
  YARA Rule: CVE-2026-5188
  Description: Generic vulnerability class detection for CVE-2026-5188 (CWE-191)
  Author: CyberDudeBivash Sentinel APEX(TM) GOC
  Date: 2026-04-10
  Reference: https://nvd.nist.gov/vuln/detail/CVE-2026-5188
*/
rule CVE_2026_5188_generic_vuln_indicator {
    meta:
        cve = "CVE-2026-5188"
        cwe = "CWE-191"
        description = "Vulnerability artifact indicator for CVE-2026-5188"
        author = "CyberDudeBivash Sentinel APEX v44.0"
        date = "2026-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-5188"
        severity = "REVIEW"
        context = "Vulnerability detection - consult NVD for precise scope"

    strings:
        $cve_ref = "CVE-2026-5188" ascii nocase
        $nvd_ref = "nvd.nist.gov" ascii

    condition:
        any of ($*)
}

8. DEFENSIVE RECOMMENDATIONS

The following recommendations are scoped to the verified vulnerability and its actual security impact. Generic security hardening guidance is provided where relevant but clearly distinguished from vulnerability-specific actions.

Vulnerability-Specific Actions (Primary)

Immediate - Apply Vendor Patches: Deploy all patches referenced in the NVD entry for CVE-2026-5188.
Verify Patch Deployment: Confirm patched versions are deployed across all affected systems using your vulnerability management platform (Qualys, Tenable, Rapid7).
Monitor for Exploitation: Enable enhanced monitoring for exploitation indicators relevant to the CVSS attack vector () and CWE class (CWE-191).

General Hardening (Secondary)

Asset Inventory: Maintain an up-to-date inventory of all deployed application versions to enable rapid identification of exposure when new CVEs are published.
Vulnerability Management Program: Cross-reference CVE-2026-5188 against your vulnerability management platform and CISA's Known Exploited Vulnerabilities (KEV) catalog. Adjust patch priority based on your organization's threat exposure.
Patch Testing Pipeline: Establish a tested patch deployment workflow that enables critical patches to reach production within 24-72 hours of vendor release.

9. REFERENCES

[OK] AUTHORITATIVE SOURCES

Source	Reference URL	Type
NVD	https://nvd.nist.gov/vuln/detail/CVE-2026-5188	Primary - NVD Official Entry
1	https://github.com/wolfSSL/wolfssl/pull/10024

All references above are sourced from the NIST National Vulnerability Database entry for CVE-2026-5188. Security teams should consult these primary sources directly for the most current information.

10. INTELLIGENCE CONFIDENCE ASSESSMENT

Signal	Factor	Confidence	Notes
[OK]	CWE Classification Confirmed	HIGH	Weakness class verified by NVD
[OK]	1 Reference(s) Available	HIGH	Vendor and third-party sources linked in NVD
[i]	CISA KEV Status	N/A	Not confirmed in CISA Known Exploited Vulnerabilities catalog at time of report generation
->	OVERALL INTELLIGENCE CONFIDENCE	MEDIUM	Partial NVD verification. Consult vendor advisories for additional confirmation.

Methodology Transparency

This report was generated by the CYBERDUDEBIVASH Sentinel APEX(TM) CVE-Verified Report Engine v44.0. All technical claims are sourced exclusively from: (1) the NIST National Vulnerability Database REST API v2 (CVE-2026-5188), (2) CWE/MITRE classification data, and (3) CVSS vector mechanical interpretation. No keyword-driven narrative templates, machine learning content generation, or speculative attack chain injection were used in producing the verified sections (Sections 1-5) of this report.

Section 6 (Threat Intelligence Context) is explicitly labeled as analytical hypothesis and is clearly separated from verified intelligence throughout the report.

CYBERDUDEBIVASH SENTINEL APEX(TM)

Global Threat Intelligence Platform

Report ID: CDB-CVE-2026-0410-0B82AA | Generated: 2026-04-10 06:06:06 UTC

This advisory is produced for defensive intelligence purposes. All claims verified against NIST NVD. Distribution: TLP:CLEAR.