Vulnerability CriticalRUSTSEC-2021-0069 · lettre
RUSTSEC-2021-0069: SMTP command injection in body
Short answerA security vulnerability in the lettre crate: SMTP command injection in body. GitHub rates it Critical. Fixed in 0.10.0-rc.3, 0.9.6: update to a fixed version.
| Crate | lettre |
|---|---|
| Type | Vulnerability (format-injection) |
| Affected versions | From 0.7.0 before 0.9.6; from 0.10.0-alpha.1 before 0.10.0-rc.3. |
| Fixed in | 0.10.0-rc.3, 0.9.6 |
| Severity | Critical (GitHub rating) |
| Published | 2021-05-22 |
| Last changed | 2023-11-08 |
| Also known as | CVE-2021-38189, GHSA-qc36-q22q-cjw3 |
| Affected functions | lettre::smtp::SmtpTransport::send, lettre::transport::smtp::SmtpTransport::send, lettre::transport::smtp::SmtpTransport::send_raw |
What to do
- See which version you have:
cargo tree -i lettre(it also shows which of your dependencies pulls it in). - Update within your version requirement:
cargo update -p lettre. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for examplelettre = "0.9.6") or update the dependency that pulls it in. - Check again with
cargo audit, or paste your Cargo.lock into our Cargo.toml checker.
Details from the advisory
Affected versions of lettre allowed SMTP command injection through an attacker's controlled message body. The module for escaping lines starting with a period wouldn't catch a period that was placed after a double CRLF sequence, allowing the attacker to end the current message and write arbitrary SMTP commands after it.
The flaw is fixed by correctly handling consecutive CRLF sequences.
References
- Package: crates.io/crates/lettre
- Advisory: rustsec.org/advisories/RUSTSEC-2021-0069.html
- Web: github.com/lettre/lettre/pull/627/commits/93458d01fed0ec81c0e7b4e98e6f35961356fae2
From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.
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