Vulnerability · Published Aug 18, 2026 · Assigned by GitHub_M
CVE-2026-53533aiosmtplib: SMTP command injection via CR/LF in sender/recipient address
Medium 6.9
In plain English
A medium-severity command injection in aiosmtplib from cole. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | aiosmtplib | no fix listed | DEBIAN-CVE-2026-53533 |
| Debian:13 | aiosmtplib | no fix listed | DEBIAN-CVE-2026-53533 |
| Debian:14 | aiosmtplib | 5.1.2-1 | DEBIAN-CVE-2026-53533 |
| PyPI | aiosmtplib | 5.1.1 | PYSEC-2026-2338 |
| PyPI | aiosmtplib | 5.1.1 | GHSA-v3q9-hj7j-63hq |
| Ubuntu:22.04:LTS | aiosmtplib | no fix listed | UBUNTU-CVE-2026-53533 |
| Ubuntu:26.04:LTS | aiosmtplib | no fix listed | UBUNTU-CVE-2026-53533 |
| Ubuntu:26.10 | aiosmtplib | no fix listed | UBUNTU-CVE-2026-53533 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| cole | aiosmtplib | < 5.1.1 |
Weakness: CWE-77, CWE-93 · 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
References
- https://github.com/cole/aiosmtplib/security/advisories/GHSA-v3q9-hj7j-63hq x_refsource_CONFIRM
- https://github.com/cole/aiosmtplib/commit/8eaf6efc9a8f59e2e09d3ef11246a058c46bd3ba x_refsource_MISC
- https://github.com/cole/aiosmtplib/releases/tag/v5.1.1 x_refsource_MISC