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Thu, 20 Aug 2026 20:30:00 +0000
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ssvc
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Thu, 20 Aug 2026 14:45:00 +0000
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| Description | aiosmtplib is an asynchronous SMTP client for use with asyncio. Prior to 5.1.2, SMTPProtocol.start_tls in src/aiosmtplib/protocol.py consumes the server's 220 response and starts the TLS handshake without clearing SMTPProtocol._buffer. An active network attacker can place attacker-chosen SMTP response lines after the plaintext 220 response in the same network segment. The method then calls loop.start_tls; those bytes survive the transport upgrade and are parsed as the first response from inside the TLS session, desynchronizing subsequent SMTP command and response pairs. Connections using start_tls=True or opportunistic STARTTLS are affected, while connections using use_tls=True are not. This issue is fixed in version 5.1.2. | |
| Title | aiosmtplib: STARTTLS response injection | |
| Weaknesses | CWE-74 | |
| References |
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| Metrics |
cvssV3_1
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Projects
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Status: PUBLISHED
Assigner: GitHub_M
Published:
Updated: 2026-08-20T20:00:21.869Z
Reserved: 2026-06-16T23:11:20.213Z
Link: CVE-2026-55558
Updated: 2026-08-20T20:00:18.930Z
Status : Received
Published: 2026-08-20T15:17:31.980
Modified: 2026-08-20T20:17:35.560
Link: CVE-2026-55558
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OpenCVE Enrichment
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