CVE-2026-90467

aiosmtplib before 5.1.3 ESMTP Parameter Injection via unvalidated addresses

Published Sep 12, 2026 CVSS 4.0 · 6.3 Medium EPSS < 1% KEV · Not listed

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.

Analysis

Technical impact

aiosmtplib is a Python library that sends email via SMTP. In versions prior to 5.1.3 it does not validate email address inputs that are supplied to the MAIL FROM and RCPT TO commands. Attackers can craft addresses containing spaces and angle brackets to embed ESMTP parameters such as AUTH, NOTIFY, or ORCPT, allowing them to forge a sender identity or redirect delivery notifications to arbitrary third parties. execution but compromises the integrity of email delivery and can be used for spoofing and notification abuse.

Affected Systems

The product aiosmtplib, maintained by cole, is vulnerable in all releases before version 5.1.3. The fix that sanitizes address inputs is available in v5.1.3 and later.

Risk and Exploitability

The moderate CVSS score of 6.3 indicates that the vulnerability mainly impacts integrity. The EPSS score of less than 1 % and the fact that it is not listed in the CISA KEV suggest that exploitation is unlikely to be widespread. The likely attack vector requires only the ability to invoke the library with a crafted address; no additional privileges or network access beyond normal SMTP usage appear to be necessary.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

cole

aiosmtplib

unaffected

Version	Status	Constraints
`0`	affected	< 5.1.3
`5.1.3`	unaffected	—

No data.

Vendor Product Versions

Cole

Aiosmtplib

Version	Status	Scheme	Platform
`[0,5.1.3)`	affected	semver	—
`5.1.3`	unaffected	semver	—

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade aiosmtplib to version 5.1.3 or later, which includes address sanitization.
Implement strict validation of email address inputs in your application before passing them to aiosmtplib, rejecting any characters that could form ESMTP parameters.
Deploy monitoring that logs outgoing SMTP envelope commands and configure your SMTP server to reject or quarantine messages containing unexpected ESMTP parameters.

Generated by OpenCVE AI on September 15, 2026 at 19:00 UTC.

Tracking

Advisories

No advisories available

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements Present

User Interaction None

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact Low

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact Low

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity High

Privileges Required None

Scope Changed

Confidentiality Impact None

Integrity Impact Low

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.393% probability within 30 days)

Exploitation none

Automatable no

Technical Impact partial

References

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

History

Sep 14, 2026 9:00 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Sep 13, 2026 6:00 AM First appearance in the feed. Affected vendors updated View changes

Type	Values Removed	Values Added
First Time appeared		Cole Cole aiosmtplib
Vendors & Products		Cole Cole aiosmtplib

Sep 12, 2026 2:00 AM Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
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.
Title		aiosmtplib before 5.1.3 ESMTP Parameter Injection via unvalidated addresses
Weaknesses		CWE-88
References		https://github.com/cole/aiosmtplib https://github.com/cole/aiosmtplib/blob/v5.1.2/src/aiosmtplib/email.py https://github.com/cole/aiosmtplib/commit/2e1b210714974ccc9efd0d09a8f846cb9aeaaec2 https://github.com/cole/aiosmtplib/releases/tag/v5.1.3 https://www.vulncheck.com/advisories/aiosmtplib-before-5.1.3-esmtp-parameter-injection-via-unvalidated-addresses
Metrics		cvssV3_1 `{'score': 4, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N'}` cvssV4_0 `{'score': 6.3, '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'}`