CVE-2026-115559 (GCVE-0-2026-115559)

Vulnerability from cvelistv5 – Published: 2026-11-10 18:39 – Updated: 2026-11-10 18:39
VLAI
Title
imaplib STARTTLS serves plaintext bytes buffered before the handshake as if they came over TLS
Summary
IMAP4.starttls() wraps the socket in TLS but leaves self._readbuf, imaplib's own read-ahead buffer, untouched. Any plaintext bytes that arrived in the same recv() as the tagged OK to STARTTLS are returned by readline() after the handshake, so the client treats them as the first responses on the protected channel. A network attacker who cannot break TLS can append forged lines after the server's OK, let the handshake complete with the real server and a valid certificate, and have the client accept the forged CAPABILITY and the forged tagged completion of the next command. This is the STARTTLS command/response injection class of CVE-2011-0411.
Severity
6.3 (Medium)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Assigner
PSF CNA under the mitre root
CNA scorecard B 78/100 over 32 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Python Software Foundation CPython Affected: 0 , < 3.16.0 (python)
guessed Create a notification for this product.
Credits
digit50 (https://github.com/digit50) Jelle Zijlstra (https://github.com/JelleZijlstra) Hugo van Kemenade (https://github.com/hugovk) Seth Larson (https://github.com/sethmlarson)
Show details on NVD website
To clipboard 

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}



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