PythonApplication
CVE-2023-40217
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedAn 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.)
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceA race condition in Python's ssl module allows unauthenticated buffered data to be read from TLS server sockets that close quickly after receiving data but before SSL handshake completion. When an SSLSocket detects the socket as 'not connected,' it skips the handshake but leaves buffered data readable, bypassing client certificate authentication.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data
PythonApplication
< 3.8.18>= 3.9.0, < 3.9.18>= 3.10.0, < 3.10.13>= 3.11.0, < 3.11.5CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed Python versionRun `python --version` or `python3 --version` to get the exact version numberAffected if The version is < 3.8.18, or >= 3.9.0 and < 3.9.18, or >= 3.10.0 and < 3.10.13, or >= 3.11.0 and < 3.11.5
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Identify SSL/TLS server code using client authenticationSearch codebase for ssl.SSLContext instances with verify_mode=ssl.CERT_REQUIRED or verify_mode=2, indicating TLS client certificate authentication is enforcedAffected if Your application uses TLS client certificate authentication (CERT_REQUIRED) on server sockets and the Python version is vulnerable
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Check for rapid connection closure patternsReview TLS server implementation for code paths where sockets may close quickly after receiving data but before SSL handshake completion, such as short timeouts or early error handlingAffected if Your TLS server has connection handling that can result in sockets closing before handshake completion while data remains buffered
You are affected if your Python version falls within the affected ranges AND you operate TLS servers that rely on client certificate authentication, as the race condition can allow buffered data to be read without proper client authentication.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped3.8.183.9.183.10.13
Upgrade Python to version 3.8.18 or higher, 3.9.18 or higher, 3.10.13 or higher, or 3.11.5 or higher. For servers using TLS client authentication, verify the fix does not break expected authentication behavior.
Upgrade to Python 3.8.18, 3.9.18, 3.10.13, or 3.11.5 (or later) depending on your current major.minor version
- 1. Check the current Python version by running: python3 --version
- 2. For Python 3.8.x: Upgrade to Python 3.8.18 or later (e.g., using package manager or pyenv)
- 3. For Python 3.9.x: Upgrade to Python 3.9.18 or later
- 4. For Python 3.10.x: Upgrade to Python 3.10.13 or later
- 5. For Python 3.11.x: Upgrade to Python 3.11.5 or later
- 6. Verify the upgrade was successful by running: python3 --version
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Python
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,328.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-40217 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2023-40217 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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