Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') Affecting aiosmtplib package, versions [,5.1.2)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-AIOSMTPLIB-19233346
- published23 Aug 2026
- disclosed21 Aug 2026
- creditUnknown
Introduced: 21 Aug 2026
NewCVE-2026-55558 (opens in a new tab)How to fix?
Upgrade aiosmtplib to version 5.1.2 or higher.
Overview
aiosmtplib is an aiosmtplib is an asynchronous SMTP client for use with asyncio.
Affected versions of this package are vulnerable to Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') via the start_tls function. An attacker can inject arbitrary SMTP response lines by sending specially crafted data after the server's 220 response in the same network segment, causing desynchronization of SMTP command and response pairs after the TLS handshake.