PatchTheCVECVE-2026-53533: aiosmtplib is an asynchronous SMTP client for use with asyncio
CVE-2026-53533 is a medium-severity flaw (CVSS 6.9) affecting affected software. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
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
Why this priority
- Remotely exploitable, no login, no user action
A fixed release or distro patch exists.
Last updated 2026-10-22 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Timeline
- Published CVE record published
- Updated Record last modified
Exact fixes by distribution
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-53533?
No fixed release is listed yet. Watch the vendor advisory and apply any mitigation shown on this page.
Is CVE-2026-53533 being exploited?
CVE-2026-53533 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-53533 affect?
CVE-2026-53533 affects affected software. Severity is medium (CVSS 6.9). 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 fr
How urgent is CVE-2026-53533?
Priority 40/100. Remotely exploitable, no login, no user action