CVE-2026-66402Network attack vectorHinoki check available

Server impersonation via malformed certificate identity matching

Published Aug 1, 2026 · Updated Aug 1, 2026

Improper certificate validation in FreeRDP before 3.29.0 allows man-in-the-middle attackers to impersonate trusted RDP servers. The three verification paths truncate embedded-NUL DNS SAN values, prefer a matching Common Name over conflicting SANs, and treat DNS names as IP identities. Exploitation requires a trusted or misissued certificate chain and a network interception position; the upstream advisory demonstrates server impersonation but no memory corruption, code execution, or direct credential extraction.

CVSS severity9.3
Critical
EPSS probability0.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Improper certificate validation in FreeRDP before 3.29.0 allows man-in-the-middle attackers to impersonate trusted RDP servers. The three verification paths truncate embedded-NUL DNS SAN values, prefer a matching Common Name over conflicting SANs, and treat DNS names as IP identities. Exploitation requires a trusted or misissued certificate chain and a network interception position; the upstream advisory demonstrates server impersonation but no memory corruption, code execution, or direct credential extraction.

The record

CVE
CVE-2026-66402
Published
Aug 1, 2026
Updated
Aug 1, 2026
Vendor
FreeRDP
Product
FreeRDP
Classifications
CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 1, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 1, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <3.29.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

FreeRDP · FreeRDPversion=0 <3.29.0

Published CVSS scores

9.8VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.3VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 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
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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