CVE-2023-40217

python: TLS handshake bypass

Published Aug 25, 2023 CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed
Description
An issue was discovered in Python before 3.8.18, 3.9.x before 3.9.18, 3.10.x before 3.10.13, and 3.11.x before 3.11.5. It primarily affects servers (such as HTTP servers) that use TLS client authentication. If a TLS server-side socket is created, receives data into the socket buffer, and then is closed quickly, there is a brief window where the SSLSocket instance will detect the socket as "not connected" and won't initiate a handshake, but buffered data will still be readable from the socket buffer. This data will not be authenticated if the server-side TLS peer is expecting client certificate authentication, and is indistinguishable from valid TLS stream data. Data is limited in size to the amount that will fit in the buffer. (The TLS connection cannot directly be used for data exfiltration because the vulnerable code path requires that the connection be closed on initialization of the SSLSocket.)

Analysis

No analysis available yet

Remediation

No remediation available yet

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-3575-1 python2.7 security update
Debian DLA Debian DLA DLA-3614-1 python3.7 security update
Debian DLA Debian DLA DLA-3948-1 pypy3 security update
Debian DLA Debian DLA DLA-3980-1 python3.9 security update
EUVD EUVD EUVD-2023-44814 An issue was discovered in Python before 3.8.18, 3.9.x before 3.9.18, 3.10.x before 3.10.13, and 3.11.x before 3.11.5. It primarily affects servers (such as HTTP servers) that use TLS client authentication. If a TLS server-side socket is created, receives data into the socket buffer, and then is closed quickly, there is a brief window where the SSLSocket instance will detect the socket as "not connected" and won't initiate a handshake, but buffered data will still be readable from the socket buffer. This data will not be authenticated if the server-side TLS peer is expecting client certificate authentication, and is indistinguishable from valid TLS stream data. Data is limited in size to the amount that will fit in the buffer. (The TLS connection cannot directly be used for data exfiltration because the vulnerable code path requires that the connection be closed on initialization of the SSLSocket.)
Ubuntu USN Ubuntu USN USN-6513-1 Python vulnerabilities
Ubuntu USN Ubuntu USN USN-6513-2 Python vulnerability
Ubuntu USN Ubuntu USN USN-6891-1 Python vulnerabilities
Ubuntu USN Ubuntu USN USN-7180-1 Python vulnerabilities
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
mitre
Published
Updated
Nov 3, 2025, 9:49 PM
Reserved
Aug 10, 2023, 12:00 AM
Status
Modified
Published
Aug 25, 2023, 1:15 AM
Modified
Jun 17, 2026, 6:16 AM
Severity
Important
Public date
Aug 25, 2023, 12:00 AM