CVE-2020-28247

Argument injection in lettre

References

• RUSTSEC-2020-0069
• CVE-2020-28247

Affected versions of lettre allowed argument injection to the sendmail command. It was possible, using forged to addresses, to pass arbitrary arguments to the sendmail executable.

Depending on the implementation (original sendmail, postfix, exim, etc.) it could be possible in some cases to write email data into abritrary files (using sendmail's logging features).

NOTE: This vulnerability only affects the sendmail transport. Others, including smtp, are not affected.

Untrusted input is inserted into a command that is later executed by the application, allowing the attacker to alter the intent of that command. Typical impact: arbitrary command execution in the application's environment.

CVE-2020-28247 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.9.5, 0.8.4, 0.7.1); upgrading removes the vulnerable code path.

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The flaw is corrected by modifying the executed command to stop parsing arguments before passing the destination addresses.

1. What is CVE-2020-28247? CVE-2020-28247 is a medium-severity command injection vulnerability in lettre (rust), affecting versions >= 0.9.0, < 0.9.5. It is fixed in 0.9.5, 0.8.4, 0.7.1. Untrusted input is inserted into a command that is later executed by the application, allowing the attacker to alter the intent of that command.
2. How severe is CVE-2020-28247? CVE-2020-28247 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of lettre are affected by CVE-2020-28247? lettre (rust) versions >= 0.9.0, < 0.9.5 is affected.
4. Is there a fix for CVE-2020-28247? Yes. CVE-2020-28247 is fixed in 0.9.5, 0.8.4, 0.7.1. Upgrade to this version or later.
5. Is CVE-2020-28247 exploitable, and should I be worried? Whether CVE-2020-28247 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2020-28247 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2020-28247?
   • Upgrade lettre to 0.9.5 or later
   • Upgrade lettre to 0.8.4 or later
   • Upgrade lettre to 0.7.1 or later

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