CVE-2021-45100Network attack vector

Cleartext SMB disclosure via invalid encryption capability flag

Published Dec 16, 2021 · Updated Aug 4, 2024

Cleartext transmission in ksmbd through 3.4.2 on Linux kernel through 5.15.8 allows remote attackers to read SMB data via network interception. During SMB 3.1.1 negotiation, ksmbd incorrectly advertises SMB2_GLOBAL_CAP_ENCRYPTION, prompting Windows 10 to disable encryption while the server accepts the plaintext session. Exposure requires SMB3 encryption to be enabled, an SMB 3.1.1 Windows 10 client, and remote attackers able to observe the network path.

CVSS severity7.5
High
EPSS probability0.91%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cleartext transmission in ksmbd through 3.4.2 on Linux kernel through 5.15.8 allows remote attackers to read SMB data via network interception. During SMB 3.1.1 negotiation, ksmbd incorrectly advertises SMB2_GLOBAL_CAP_ENCRYPTION, prompting Windows 10 to disable encryption while the server accepts the plaintext session. Exposure requires SMB3 encryption to be enabled, an SMB 3.1.1 Windows 10 client, and remote attackers able to observe the network path.

The record

CVE
CVE-2021-45100
Published
Dec 16, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-319, T1040
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 16, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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

5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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.

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

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-319Cleartext Transmission of Sensitive Information
T1040Network Sniffing

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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