CVE-2021-38373Public exploitNetwork attack vector

Message disclosure and tampering via skipped STARTTLS

Published Aug 10, 2021 · Updated Aug 4, 2024

Cleartext transmission in KMail 19.12.3 allows man-in-the-middle attackers to read or alter SMTP messages when STARTTLS is bypassed. KSMTP starts TLS from LoginJob, so sessions without SMTP authentication create no LoginJob and proceed without the configured upgrade. The flaw is reachable only when STARTTLS is selected while "Server requires authentication" is cleared, exposing message content and integrity on the client-to-server path.

CVSS severity5.3
Medium
EPSS probability0.53%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cleartext transmission in KMail 19.12.3 allows man-in-the-middle attackers to read or alter SMTP messages when STARTTLS is bypassed. KSMTP starts TLS from LoginJob, so sessions without SMTP authentication create no LoginJob and proceed without the configured upgrade. The flaw is reachable only when STARTTLS is selected while "Server requires authentication" is cleared, exposing message content and integrity on the client-to-server path.

The record

CVE
CVE-2021-38373
Published
Aug 10, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-77, CWE-319, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 10, 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

5.3NIST NVDCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N
3.5NIST NVDAV:N/AC:M/Au:S/C:P/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 11, 2026Sep 17, 2026
Latest reporting daySep 17, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-77Improper Neutralization of Special Elements used in a Command ('Command Injection')
CWE-319Cleartext Transmission of Sensitive Information
T1557Adversary-in-the-Middle

Public exploit references

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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