CVE-2021-38189: An issue was discovered in the lettre crate before 0.9.6 for Rust

Q: How do I fix CVE-2021-38189?

lettre: upgrade to 0.9.6. Exact commands for each OS are on this page.

Q: Is CVE-2021-38189 being exploited?

CVE-2021-38189 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-38189 affect?

CVE-2021-38189 affects lettre. Severity is critical (CVSS 9.8). An issue was discovered in the lettre crate before 0.9.6 for Rust. In an e-mail message body, an attacker can place a . character after two sequences and then inject arbitrary SMTP commands.

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2021-38189 is a critical-severity flaw (CVSS 9.8) affecting lettre. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in the lettre crate before 0.9.6 for Rust. In an e-mail message body, an attacker can place a . character after two <CR><LF> sequences and then inject arbitrary SMTP commands.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.5% (top 26%)
CISA exploited list	No
Weakness	CWE-77
Published	2021-08-08
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: lettre

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

Am I affected?

Timeline

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

lettre lettre UPGRADE

Affected: < 0.9.6 · 0.10.0 alpha1 · 0.10.0 alpha2 · 0.10.0 alpha3 · 0.10.0 alpha4 · 0.10.0 alpha5 · 0.10.0 beta1 · 0.10.0 beta2

Fixed in: 0.9.6

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 0.9.6 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade lettre

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade lettre

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2021-38189?

lettre: upgrade to 0.9.6. Exact commands for each OS are on this page.

Is CVE-2021-38189 being exploited?

CVE-2021-38189 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-2021-38189 affect?

CVE-2021-38189 affects lettre. Severity is critical (CVSS 9.8). An issue was discovered in the lettre crate before 0.9.6 for Rust. In an e-mail message body, an attacker can place a . character after two <CR><LF> sequences and then inject arbitrary SMTP commands.

How urgent is CVE-2021-38189?

Priority 63/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2020-28247 MEDIUM 5.3 UPGRADE The lettre library through 0.10.0-alpha for Rust allows arbitrary sendmail option injection via transport/send

References

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