aiosmtplib vulnerable to SMTP command injection via CR/LF in sender/recipient addressGHSA-v3q9-hj7j-63hq
GHSA-v3q9-hj7j-63hq is a CWE-77 vulnerability in aiosmtplib. A fix is available for aiosmtplib — see the affected versions and patch details below.
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-v3q9-hj7j-63hq.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
Real-World Exposure
aiosmtplibReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
aiosmtplib's SMTP.mail(), SMTP.rcpt(), SMTP.vrfy() and SMTP.expn() send the caller-supplied email address to the server without rejecting embedded CR/LF (\r\n) bytes. An address that contains a CR/LF is written verbatim onto the SMTP control connection, so the bytes after the CRLF are framed by the server as one or more additional, standalone SMTP command lines. A caller that passes an attacker-influenced sender or recipient address into mail()/rcpt() (or vrfy()/expn()) therefore allows SMTP command injection (CWE-93 / CWE-77): the attacker can smuggle arbitrary SMTP verbs such as MAIL FROM, RCPT TO, RSET, DATA, or AUTH into the session. Injected commands will cause the SMTP instance to hang, but all commands required to complete the envelope could be sent in one address string.
The SMTP.sendmail() command will pass sender and recipient addresses verbatim through to SMTP.mail() & SMTP.rcpt(), and so is also vulnerable. SMTP.send_message() is not affected.
Impact
Severity: medium. Type: SMTP protocol command injection (CWE-93 — Improper Neutralization of CRLF Sequences; CWE-77 — Command Injection).
When an application built on aiosmtplib derives the envelope sender or any recipient from data an attacker can influence (a web form etc.) and passes it to mail()/rcpt() (directly, or via sendmail()/send() without a Message object), the attacker can:
- desynchronize the command/response pipeline and cause the aiosmtplib client to hang, resulting in a possible denial of service
- inject multiple commands in one address to send an arbitrary message
The address only needs to reach mail()/rcpt()/vrfy()/expn(); no attacker control over the SMTP server is required.
Vulnerable versions
Affected version: aiosmtplib 5.1.0 (latest at time of report) and all earlier releases.
Credit
Reported by tonghuaroot.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | aiosmtplib | all versions | 5.1.1pip install --upgrade 'aiosmtplib==5.1.1' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for aiosmtplib, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update aiosmtplib to 5.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-v3q9-hj7j-63hq is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
Frequently Asked Questions
Is GHSA-v3q9-hj7j-63hq in your dependencies?
Find it across PyPI, including transitive dependencies.