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[3.10] gh-108310: Fix CVE-2023-40217: Check for & avoid the ssl pre-close flaw #108318

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merged 1 commit into from
Aug 22, 2023

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@ambv ambv commented Aug 22, 2023

Instances of ssl.SSLSocket were 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.

…ose flaw

Instances of `ssl.SSLSocket` were 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.

Co-Authored-By: Gregory P. Smith [Google LLC] <[email protected]>
@ambv ambv requested a review from tiran as a code owner August 22, 2023 17:01
@ambv ambv merged commit 37d7180 into python:3.10 Aug 22, 2023
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@ambv ambv deleted the cve-2023-40217-3.10 branch August 22, 2023 18:00
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2 participants