CVE-2026-53533
MediumCVSS 6.9Exploitation Probability (EPSS)
Low risk32th percentile - higher than 32% of all known CVEs
Summary
aiosmtplib before 5.1.1 does not reject addresses containing CR or LF bytes in SMTP.mail(), SMTP.rcpt(), SMTP.vrfy(), and SMTP.expn(). Data after the line break is framed as additional standalone SMTP command lines, allowing an attacker 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.
Risk Assessment
An attacker can inject SMTP commands, potentially leading to sending unauthorized messages, service hang, or compromising email communication integrity.
Recommendation
Update aiosmtplib to version 5.1.1 or later.
Original NVD description (English source)
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.