CVE-2021-38373: In KDE KMail 19.12.3 (aka 5.13.3), the SMTP STARTTLS option is not honored (and cleartext messages are sent) u

Routine

MEDIUM 5.3DOWNGRADE

CVE-2021-38373 is a medium-severity flaw (CVSS 5.3) affecting kmail. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In KDE KMail 19.12.3 (aka 5.13.3), the SMTP STARTTLS option is not honored (and cleartext messages are sent) unless "Server requires authentication" is checked.

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.5% (top 55%)
CISA exploited list	No
Weakness	CWE-77, CWE-319
Published	2021-08-10
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: kde

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-08-10 15:15 UTCPublished CVE record published
2026-06-17 04:01 UTCUpdated Record last modified

kde kmail DOWNGRADE

Affected: 19.12.3

Fixed in: no fixed release known

Safe to downgrade to: a release before 19.12.3

1. Check installed version

apt-cache policy kmail || rpm -q kmail || kmail --version

2. No fixed release: DOWNGRADE to a release before 19.12.3 (Debian / Ubuntu)

apt-cache madison kmail sudo apt install kmail=<VERSION_BEFORE_19.12.3> sudo apt-mark hold kmail

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list kmail sudo dnf downgrade kmail-<VERSION_BEFORE_19.12.3> sudo dnf versionlock add kmail

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-38373?

kmail: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-38373 being exploited?

CVE-2021-38373 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-38373 affect?

CVE-2021-38373 affects kmail. Severity is medium (CVSS 5.3). In KDE KMail 19.12.3 (aka 5.13.3), the SMTP STARTTLS option is not honored (and cleartext messages are sent) unless "Server requires authentication" is checked.

How urgent is CVE-2021-38373?

Priority 30/100. No elevated risk signals yet.

Related CVEs

CVE-2020-15954 MEDIUM 6.5 DOWNGRADE MITIGATE KDE KMail 19.12.3 (aka 5.13.3) engages in unencrypted POP3 communication during times when the UI indicates th
CVE-2020-11880 MEDIUM 6.5 UPGRADE An issue was discovered in KDE KMail before 19.12.3
CVE-2019-10732 MEDIUM 4.3 DOWNGRADE MITIGATE In KDE KMail 5.2.3, an attacker in possession of S/MIME or PGP encrypted emails can wrap them as sub-parts wit
CVE-2017-9604 HIGH 7.5 UPGRADE UPGRADE KDE kmail before 5.5.2 and messagelib before 5.5.2, as distributed in KDE Applications before 17.04.2, do not
CVE-2016-7968 MEDIUM 6.5 UPGRADE KMail since version 5.3.0 used a QWebEngine based viewer that had JavaScript enabled

References

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