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[3.12] gh-108310: Fix CVE-2023-40217: Check for & avoid the ssl pre-close flaw#108316
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…ose flawInstances of `ssl.SSLSocket` were vulnerable to a bypass of the TLS handshakeand included protections (like certificate verification) and treating sentunencrypted data as if it were post-handshake TLS encrypted data.The vulnerability is caused when a socket is connected, data is sent by themalicious peer and stored in a buffer, and then the malicious peer closes thesocket within a small timing window before the other peers’ TLS handshake canbegin. After this sequence of events the closed socket will not immediatelyattempt a TLS handshake due to not being connected but will also allow thebuffered data to be read as if a successful TLS handshake had occurred.Co-Authored-By: Gregory P. Smith [Google LLC] <greg@krypto.org>
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blaisep added a commit to blaisep/cpython that referenced this pull requestMay 22, 2025
WIP tofixpython#106318 using the contributions frompython#105670
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Instances of
ssl.SSLSocketwere vulnerable to a bypass of the TLS handshake and included protections (like certificate verification) and treating sent unencrypted data as if it were post-handshake TLS encrypted data.The vulnerability is caused when a socket is connected, data is sent by the malicious peer and stored in a buffer, and then the malicious peer closes the socket within a small timing window before the other peers’ TLS handshake can begin. After this sequence of events the closed socket will not immediately attempt a TLS handshake due to not being connected but will also allow the buffered data to be read as if a successful TLS handshake had occurred.