---
id: CVE-2026-90467
title: >-
  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
summary: >-
  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…
severity: medium
cvss: 4
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N'
cwe:
  - CWE-88
vendor: cole
product: aiosmtplib
affected:
  - aiosmtplib < 5.1.3
published: '2026-09-12'
updated: '2026-09-23'
sourceUpdated: '2026-09-23T17:17:44.240'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-90467'
references:
  - url: 'https://github.com/cole/aiosmtplib'
    label: disclosure@vulncheck.com
  - url: 'https://github.com/cole/aiosmtplib/blob/v5.1.2/src/aiosmtplib/email.py'
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/cole/aiosmtplib/commit/2e1b210714974ccc9efd0d09a8f846cb9aeaaec2
    label: disclosure@vulncheck.com
  - url: 'https://github.com/cole/aiosmtplib/releases/tag/v5.1.3'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/aiosmtplib-before-5.1.3-esmtp-parameter-injection-via-unvalidated-addresses
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
epss: 0.00229
epssPercentile: 0.13949
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-14T16:14:45.700619Z'
ingestedAt: '2026-09-14T15:23:07.484Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.