CVE-2026-45389Network attack vector

Client impersonation via missing certificate-purpose validation

Published Jun 15, 2026 · Updated Jun 15, 2026

Improper certificate validation in OCaml-TLS before 2.1.0 allows remote attackers to impersonate mTLS clients using trusted server certificates. The validateCerts and answerClientCertificate paths call validateChain but omit KeyUsage digitalSignature and ExtendedKeyUsage clientAuth checks on the presented leaf. Exploitation requires mTLS, a chain-valid certificate under the listener's trust store, and an application that relies on TLS validation alone; successful handshakes grant the certificate subject an authenticated client identity.

CVSS severity7.4
High
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate validation in OCaml-TLS before 2.1.0 allows remote attackers to impersonate mTLS clients using trusted server certificates. The validateCerts and answerClientCertificate paths call validateChain but omit KeyUsage digitalSignature and ExtendedKeyUsage clientAuth checks on the presented leaf. Exploitation requires mTLS, a chain-valid certificate under the listener's trust store, and an application that relies on TLS validation alone; successful handshakes grant the certificate subject an authenticated client identity.

The record

CVE
CVE-2026-45389
Published
Jun 15, 2026
Updated
Jun 15, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-295, T1078
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 15, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 15, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.4CISA-ADPCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
7.4OCaml Security Response TeamCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1078Valid Accounts

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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