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Improper Certificate ValidationWeakness · CWE-295

CVE-2026-45389

HIGH · 7.4 CVSS v3.1 Published 2026-06-15
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
83/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In OCaml-TLS before 2.1.0, the server implementation does insufficient checks of the certificate provided by the client (when doing client authentication), which allows impersonation with certificates that are not meant for client authentication (because of KeyUsage and ExtendedKeyUsage).

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In OCaml-TLS before version 2.1.0, the TLS server implementation fails to properly validate the KeyUsage and ExtendedKeyUsage certificate extensions during client certificate authentication. This allows an attacker to use certificates not intended for client authentication (e.g., SSL/TLS server certificates) to impersonate legitimate clients, bypassing the client authentication mechanism.

MitigationUpgrade OCaml-TLS to version 2.1.0 or later which implements proper certificate purpose validation (KeyUsage/ExtendedKeyUsage checking) during client authentication.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify OCaml-TLS installation
    Check for OCaml-TLS library in your project's dependency files (e.g., opam file, dune-project, or Makefile) or list installed OCaml packages using 'opam list | grep tls'
    Affected if OCaml-TLS is present in the environment
  2. Determine installed OCaml-TLS version
    Run 'opam show tls' or check the version in your opam/dune lock file to identify the exact version number
    Affected if Version is before 2.1.0 (e.g., 2.0.x, 1.x.x series)
  3. Verify client certificate authentication is in use
    Review your TLS server configuration or code to confirm client authentication (client_cert_required or similar option) is enabled
    Affected if Client certificate authentication is configured and active
  4. Inspect certificate validation logic for KeyUsage/ExtendedKeyUsage checks
    Examine the OCaml-TLS source code or configuration for proper certificate purpose validation during client auth - look for validation of keyUsage (digitalSignature) and extendedKeyUsage (clientAuth) extensions
    Affected if The validation does not check KeyUsage/ExtendedKeyUsage extensions for client certificates

You are affected if OCaml-TLS versions before 2.1.0 are installed AND client certificate authentication is enabled, since the server fails to validate certificate purpose extensions allowing unauthorized client impersonation.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade OCaml-TLS to version 2.1.0 or later which implements proper certificate purpose validation (KeyUsage/ExtendedKeyUsage checking) during client authentication.

Recommended fix Moderate confidence

OCaml-TLS 2.1.0

  1. Identify all OCaml-TLS deployments in your infrastructure that perform client certificate authentication
  2. Check the current OCaml-TLS version using your package manager or project dependencies
  3. Upgrade OCaml-TLS to version 2.1.0 or later
  4. After upgrading, verify that client certificate authentication still functions correctly for legitimate clients with proper KeyUsage and ExtendedKeyUsage extensions
  5. Test that the server now properly rejects client certificates lacking the appropriate key usage flags (e.g., keyCertSign for CA, digitalSignature for end-entity certificates)

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-45389 in production — separate from our analysis above.

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What this is

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