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Forged Trust: Improper Certificate Validation in wolfSSL

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CVE-2026-5194 is a critical vulnerability affecting the wolfSSL cryptographic library, a widely used TLS/SSL implementation deployed across embedded systems, IoT devices, networking equipment, and applications.

The issue impacts certificate validation logic and may allow improperly validated certificates to be accepted. This can result in systems trusting certificates that should otherwise be rejected.

The vulnerability has been assigned a CVSS score of 9.3, indicating a critical severity level.

Vulnerability and Technical Details

Root Cause

CVE-2026-5194 is classified as an improper certificate validation (CWE-295) vulnerability. The issue arises due to missing validation checks during signature verification, specifically:

  • Lack of enforcement of minimum digest (hash) size requirements
  • Lack of proper validation of the Object Identifier (OID) associated with the signature

Because of these missing checks, wolfSSL may accept signatures that do not meet expected validation criteria.

Affected Verification Context

The vulnerability affects certificate verification involving ECDSA or ECC signatures. It is triggered in configurations where EdDSA or ML-DSA are enabled alongside ECC-based verification.

Due to improper validation:

  • Certificates containing invalid or insufficient digest values may be accepted
  • Certificate validation may succeed even when expected validation checks are not properly enforced

Impact and Exploitation Potential

Core Impact

The vulnerability allows:

  • Acceptance of improperly validated certificates
  • Potential for impersonation of trusted entities

This affects systems that rely on wolfSSL for certificate-based authentication.

Exploitation Characteristics

According to the CVSS assessment, the vulnerability is network exploitable and has low attack complexity. At the moment, active exploitation of this vulnerability has not been reported.

wolfSSL is used in a range of systems, including:

  • IoT devices
  • Routers and networking equipment
  • Embedded systems
  • Applications using TLS functionality

Products Affected

The wolfSSL cryptographic library below version 5.9.1 is affected.

Systems are affected when:

  • wolfSSL is used for certificate validation
  • ECC-based verification is enabled
  • EdDSA or ML-DSA support is enabled

Solution

The issue has been addressed in wolfSSL version 5.9.1. This version introduces validation checks for signature-related parameters and digest size.

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