CVE-2026-53533
Publication date 18 August 2026
Last updated 2 September 2026
Ubuntu priority
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| aiosmtplib | 26.04 LTS resolute |
Needs evaluation
|
| 24.04 LTS noble | Not in release | |
| 22.04 LTS jammy |
Needs evaluation
|
Severity score breakdown
CVSS version: CVSS v4.0
Base score
6.9 · Medium
Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:H/SA:N