What is the CVSS score of CVE-2026-5501?

CVE-2026-5501 has a CVSS 4.0 base score of 8.6 (High). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N. EPSS exploitation probability: 0.0%.

Is there a public PoC exploit available for CVE-2026-5501?

Yes, a public proof-of-concept exploit is available for CVE-2026-5501. Prioritise patching immediately. EPSS: 0.0%.

How to fix or mitigate CVE-2026-5501?

Within 24 hours: inventory all nginx and HAProxy instances using wolfSSL instead of OpenSSL; verify wolfSSL version and OpenSSL compatibility layer status in production via 'strings' or version inspection. Within 7 days: contact wolfSSL (Linuxppc/stm32) for patch timeline and interim guidance; implement network segmentation to restrict certificate-issuing traffic if feasible. Within 30 days: deploy vendor-released patch immediately upon availability; as interim measure, migrate affected nginx/HAProxy instances to native OpenSSL if operationally feasible to eliminate OpenSSL compatibility layer dependency.

Wolfssl CVE-2026-5501

EUVD-2026-21294 HIGH

Improper Certificate Validation (CWE-295)

2026-04-10 wolfSSL

GHSA-hg75-4cmp-f367

Information Disclosure OpenSSL Nginx Wolfssl

8.6

CVSS 4.0 · NVD

View

Attack ChainAIDerived

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

Access

Obtain legitimate leaf certificate from trusted CA
Delivery

Construct forged certificate with untrusted intermediate CA:FALSE
Exploit

Supply crafted chain to wolfSSL_X509_verify_cert
Execution

Bypass signature validation
Impact

Return success and grant unauthorized access

Vulnerability Assessment

Weakness	CWE CWE-295 OWASP Top 10:2025 A07:2025 - Authentication Failures ASVS 5.0 V12 - Secure Communication Certificate validation
Exploitation Conditions	Requires authenticated access (PR:L) to applications using wolfSSL's OpenSSL compatibility layer function wolfSSL_X509_verify_cert. Attacker must supply crafted certificate chain with untrusted intermediate (CA:FALSE) signed by trusted root. Native wolfSSL TLS handshake (ProcessPeerCerts) unaffected.
Impact	CVSS 8.6 reflects high confidentiality/integrity impact via authenticated network access. Moderate observed exploitation activity. Critical for nginx/haproxy deployments using wolfSSL's OpenSSL compatibility layer directly; native TLS handshake unaffected. Requires valid leaf certificate from trusted CA and authenticated session, limiting blast radius to environments with certificate-based authentication enabled.
Exploit ScenarioDerived	Attacker obtains legitimate leaf certificate from trusted CA (e.g., Let's Encrypt). Supplies forged certificate chain with untrusted intermediate (CA:FALSE, validly signed by root) to application calling wolfSSL_X509_verify_cert. Function incorrectly returns success without validating leaf signature, allowing arbitrary subject name/public key impersonation.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

No patch listed yet 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Apr 10, 2026

Certificate chain validation bypass in wolfSSL's OpenSSL compatibility layer allows authenticated network attackers to forge arbitrary certificates. Attackers possessing any legitimate leaf certificate from a trusted CA can craft fraudulent certificates for any subject name with arbitrary keys, bypassing signature verification when an untrusted CA:FALSE intermediate is inserted. Affects nginx and haproxy integrations using wolfSSL's OpenSSL compatibility API; native wolfSSL TLS handshake (ProcessPeerCerts) not vulnerable. No public exploit identified at time of analysis.

RemediationAI

Upstream fix available (PR/commit); released patched version not independently confirmed. Review vendor advisory and apply patch from https://github.com/wolfSSL/wolfssl/pull/10102 when released version becomes available. Organizations unable to patch immediately should migrate affected nginx/haproxy instances to native wolfSSL TLS handshake paths (ProcessPeerCerts) which are not vulnerable, or temporarily replace wolfSSL with alternative TLS libraries (OpenSSL, BoringSSL) until patched release confirmed. Audit certificate validation workflows in custom applications using wolfSSL OpenSSL compatibility layer. Monitor wolfSSL security advisories for official patched version announcement and upgrade guidance.

Affected VersionsENISA

wolfSSL 0 ≤5.9.0

Affected Packages

euvd wolfssl no fix

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

Root cause: wolfSSL_X509_verify_cert (CWE-295) fails to validate leaf certificate signature when chain contains untrusted intermediate marked Basic Constraints CA:FALSE but legitimately signed by trusted root. Native wolfSSL validation logic correctly enforces signature checks; vulnerability isolated to OpenSSL compatibility shim layer consuming cpe:2.3:a:wolfssl:wolfssl chains.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 8.6 HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Attack Requirements

None

Privileges Required

Low

User Interaction

None

Vulnerable system: Confidentiality

High

Vulnerable system: Integrity

High

Vulnerable system: Availability

None

Subsequent system: Confidentiality

None

Subsequent system: Integrity

None

Subsequent system: Availability

None

DescriptionCVE.org

wolfSSL_X509_verify_cert in the OpenSSL compatibility layer accepts a certificate chain in which the leaf's signature is not checked, if the attacker supplies an untrusted intermediate with Basic Constraints CA:FALSE that is legitimately signed by a trusted root. An attacker who obtains any leaf certificate from a trusted CA (e.g. a free DV cert from Let's Encrypt) can forge a certificate for any subject name with any public key and arbitrary signature bytes, and the function returns WOLFSSL_SUCCESS / X509_V_OK. The native wolfSSL TLS handshake path (ProcessPeerCerts) is not susceptible and the issue is limited to applications using the OpenSSL compatibility API directly, which would include integrations of wolfSSL into nginx and haproxy.

Executive ViewAI

Why It Matters

CVE-2026-5501 is a certificate chain validation bypass in wolfSSL's OpenSSL compatibility layer affecting nginx and HAProxy deployments, allowing authenticated attackers with any legitimate certificate to forge certificates for arbitrary domains and bypass signature verification. Organizations using these web servers with wolfSSL should immediately assess exposure, as this vulnerability directly undermines TLS authentication trust and could enable man-in-the-middle attacks and credential theft without detection.

Business Impact: High

Compensating Controls

No vendor-released patch identified at time of analysis. Interim mitigations: (1) Restrict authentication to trusted internal networks only; (2) disable OpenSSL compatibility layer in wolfSSL configuration and use native wolfSSL TLS handshake (ProcessPeerCerts) if compatible with nginx/HAProxy version; (3) migrate affected web servers to standard OpenSSL until patch availability; (4) increase monitoring of certificate validation failures and unusual certificate issuance events; (5) implement mTLS with client certificate pinning to limit exposure.

Threat Intelligence Overview

EPSS Score

0.0%

Top 94% exploitable

Exploit

POC

Public exploit code exists

Social Media

Sightings

Data Quality

7 sources

Confidence: High

EUVD

NVD

CVE.org

EPSS

Vulnrichment CIRCL

GitHub

VulDB

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 HIGH

CISA KEV No

Public POC Yes

EPSS 0.0%

Patch available No

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

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

Scheduled

Exploitation

None

System Exposure· derived

Open

Automatable

Yes

Human Impact

High

Technical Impact

Total

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +43

PoC: +20

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.