Vulnerability Description
aiosmtplib is an asynchronous SMTP client for use with asyncio. Prior to 5.1.1, SMTP.mail(), SMTP.rcpt(), SMTP.vrfy(), and SMTP.expn() send caller-supplied addresses without rejecting embedded CR or LF bytes. Data after the line break is framed as additional standalone SMTP command lines, allowing an attacker who influences an envelope sender or recipient to inject commands such as MAIL FROM, RCPT TO, RSET, DATA, or AUTH. SMTP.sendmail() and SMTP.send() without a Message object pass addresses through the affected methods, while SMTP.send_message() is not affected. Successful injection can desynchronize the command-response pipeline, hang the SMTP instance, or send an arbitrary message without requiring attacker control of the SMTP server. This issue is fixed in version 5.1.1.
Related Weaknesses (CWE)
References
- https://github.com/cole/aiosmtplib/commit/8eaf6efc9a8f59e2e09d3ef11246a058c46bd3
- https://github.com/cole/aiosmtplib/releases/tag/v5.1.1
- https://github.com/cole/aiosmtplib/security/advisories/GHSA-v3q9-hj7j-63hq
FAQ
What is CVE-2026-53533?
CVE-2026-53533 is a documented vulnerability. aiosmtplib is an asynchronous SMTP client for use with asyncio. Prior to 5.1.1, SMTP.mail(), SMTP.rcpt(), SMTP.vrfy(), and SMTP.expn() send caller-supplied addresses without rejecting embedded CR or L...
How severe is CVE-2026-53533?
CVSS scoring is not yet available for CVE-2026-53533. Check NVD for updates.
Is there a patch for CVE-2026-53533?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.