VulnerabilityPublished 25 Aug 2023Updated 3 Nov 2025

CVE-2023-40217: python

Affects pythonSource CVE Database V5

Not known to be exploited · fixed in 3.11.5 : update python when convenient.

Data as of 26 Oct 2026, 12:54 UTC

Severity

Medium

Rated Medium by the CNA (mitre) · No CVSS score from NVD or the CNA

EPSS: 0.7% chance of exploitation in 30 days – higher than 56% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.11.5, 3.10.13, 3.9.18 +1

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Aug 2023
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade python to 3.11.5, 3.10.13, 3.9.18 or 3.8.18.

Affected software

Product	Affected	Fixed in
PyPIpython`pkg:pypi/python`Other threats	Affected <3.8.18 <3.9.18 <3.10.13 <3.11.5	Fixed in 3.8.18 3.9.18 3.10.13 3.11.5

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in Python versions 3.8.18, 3.9.18, 3.10.13, and 3.11.5. Users running affected versions should upgrade to these fixed releases to remediate the vulnerability. No additional mitigation actions are specified.

Description

A vulnerability in Python versions prior to 3.8.18, 3.9.18, 3.10.13, and 3.11.5 affects servers using TLS client authentication. When a TLS server-side socket is created, receives data, and is then closed quickly, there is a brief window where buffered data can be read without authentication. This data is indistinguishable from valid TLS stream data but is limited in size to the socket buffer. The issue arises because the SSLSocket instance detects the socket as not connected and does not initiate a handshake, leaving buffered data unauthenticated.

Impact

The vulnerability allows an attacker to read a limited amount of unauthenticated data from the socket buffer in TLS client-authenticated server scenarios. This could potentially lead to bypassing client certificate authentication for the buffered data. However, the data size is limited to the buffer size, and the TLS connection cannot be used directly for data exfiltration due to the requirement that the connection be closed on SSLSocket initialization. There are no known exploits in the wild.

Summary

CVE-2023-40217 is a vulnerability in Python's TLS implementation affecting versions before 3.8.18, 3.9.18, 3.10.13, and 3.11.5. It impacts server-side TLS sockets that use client certificate authentication. If such a socket receives data and is closed quickly, the SSLSocket instance may not perform the expected TLS handshake, resulting in buffered data being readable without authentication. This unauthenticated data is limited to the size of the socket buffer and cannot be used for data exfiltration because the connection must be closed during SSLSocket initialization. The vulnerability is fixed in Python versions 3.8.18, 3.9.18, 3.10.13, and 3.11.5.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Oct 2026, 22:43 UTC

Technical details

References

Community reviews

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