CVE-2021-38189: Lettre SMTP Command Injection Vulnerability

CRITICAL
Advisory Identifier: GHSA-qc36-q22q-cjw3
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CVSS 9.8
CWE-147
Published
Advisory Summary

CVE-2021-38189 is a CRITICAL (CVSS 9.8) smtp command injection vulnerability (CWE-147: Improper Neutralization of Input Terminators) affecting Lettre libraries in the crates.io ecosystem. The issue involves smtp command injection in lettre. Remediation is available by upgrading affected packages to version 0.9.6.

CVE-2021-38189 at a Glance

CVE Identifier CVE-2021-38189
GHSA Identifier GHSA-qc36-q22q-cjw3
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-147: Improper Neutralization of Input Terminators
Affected Product Lettre
Package Ecosystem crates.io
Published Date
Last Updated

Security Impact

CVSS: 9.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2021-38189

To remediate this vulnerability, upgrade all affected Lettre dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

lettre fixed: 0.9.6 
Upgrade lettre to 0.9.6
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for lettre

How to Check if You Are Affected

To determine whether your application is affected by CVE-2021-38189, inspect your project dependencies for Lettre:

inspect dependencies for lettre

Analyze the terminal output to locate any version of Lettre in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.9.6), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-147: Improper Neutralization of Input Terminators, where the product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as input terminators when they are sent to a downstream component. In Lettre, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact 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. ### Fix The flaw is fixed by correctly handling consecutive CRLF sequences. ### References * [RUSTSEC-2021-0069](https://rustsec.org/advisories/RUSTSEC-2021-0069.html)

CVE-2021-38189 Affected Lettre Versions

1 component(s)
Fixed Versions:
0.9.6
Product / Package Ecosystem Affected Versions Fixed Version
lettre
 crates.io
≥ 0.7.0
< 0.9.6
0.9.6

References

GitHub Advisory / Wiki ADVISORY
https://github.com/lettre/lettre/security/advisories/GHSA-qc36-q22q-cjw3
Lettre Source Repository REPOSITORY
https://github.com/lettre/lettre/pull/627/commits/93458d01fed0ec81c0e7b4e98e6f35961356fae2
Security Fix Commit FIX COMMIT
https://github.com/lettre/lettre/commit/8bfc20506cc5e098fe6eb3d1cafe3bea791215ce
Lettre Source Repository REPOSITORY
https://github.com/lettre/lettre
rustsec.org/advisories/rustsec-... WEB
https://rustsec.org/advisories/RUSTSEC-2021-0069.html

Frequently Asked Questions

What is CVE-2021-38189?
CVE-2021-38189 is a security vulnerability in Lettre involving SMTP command injection in lettre under CWE-147: Improper Neutralization of Input Terminators.
Which Lettre versions are affected?
Affected versions include releases prior to 0.9.6 across affected packages: lettre.
What version fixes CVE-2021-38189?
Upgrading to 0.9.6 (or the latest patched release for your respective branch) resolves the vulnerability.
Is lettre affected?
Yes, lettre is affected in releases prior to 0.9.6. Upgrade your dependency to 0.9.6 or later.
What is the CVSS score of CVE-2021-38189?
CVE-2021-38189 has a CVSS v3.1 base score of 9.8 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2021-38189?
CVE-2021-38189 is classified under CWE-147: Improper Neutralization of Input Terminators (The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as input terminators when they are sent to a downstream component.).
How can I check crates.io dependencies for CVE-2021-38189?
Run the dependency tree command: 'inspect dependencies for lettre'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qc36-q22q-cjw3",
  "modified" : "2021-08-18T18:52:26Z",
  "published" : "2021-07-12T17:03:27Z",
  "aliases" : [ "CVE-2021-38189" ],
  "summary" : "SMTP command injection in lettre",
  "details" : "### Impact\n\nAffected 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.\n\n### Fix\n\nThe flaw is fixed by correctly handling consecutive CRLF sequences.\n\n### References\n\n* [RUSTSEC-2021-0069](https://rustsec.org/advisories/RUSTSEC-2021-0069.html)\n\n\n\n",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "lettre"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.7.0"
      }, {
        "fixed" : "0.9.6"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/lettre/lettre/security/advisories/GHSA-qc36-q22q-cjw3"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lettre/lettre/pull/627/commits/93458d01fed0ec81c0e7b4e98e6f35961356fae2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/lettre/lettre/commit/8bfc20506cc5e098fe6eb3d1cafe3bea791215ce"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/lettre/lettre"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2021-0069.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-147" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-06-01T20:41:39Z",
    "nvd_published_at" : "2021-08-08T06:15:00Z"
  }
}