CVE-2021-39214
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 · uneditedmitmproxy is an interactive, SSL/TLS-capable intercepting proxy. In mitmproxy 7.0.2 and below, a malicious client or server is able to perform HTTP request smuggling attacks through mitmproxy. This means that a malicious client/server could smuggle a request/response through mitmproxy as part of another request/response's HTTP message body. While a smuggled request is still captured as part of another request's body, it does not appear in the request list and does not go through the usual mitmproxy event hooks, where users may have implemented custom access control checks or input sanitization. Unless one uses mitmproxy to protect an HTTP/1 service, no action is required. The vulnerability has been fixed in mitmproxy 7.0.3 and above.
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 confidencemitmproxy versions 7.0.2 and below contain a vulnerability allowing HTTP request smuggling attacks. A malicious server can smuggle additional HTTP requests within the body of a response, and these smuggled requests bypass mitmproxy's normal capture and event hook processing, allowing them to evade access control checks and input sanitization implemented by users.
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<= 7.0.2CVSS 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
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
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 mitmproxy versionRun `mitmproxy --version` or `pip show mitmproxy` to see the installed version numberAffected if Version is 7.0.2 or lower (e.g., 7.0.0, 6.0.2, 5.x, etc.)
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Confirm mitmproxy is actively proxying HTTP/1 trafficReview your mitmproxy configuration or running instance to verify it is handling HTTP/1 connections from clientsAffected if mitmproxy is proxying HTTP/1 traffic with a version <= 7.0.2
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Inspect proxy logs for unexpected request patternsReview mitmproxy logs or generated HAR/flow files for requests that appear without corresponding client connection entries or event hooksAffected if Smuggled requests appear in backend systems but are absent from mitmproxy flow logs or event triggers
You are affected if mitmproxy version is 7.0.2 or lower and it is actively proxying HTTP/1 connections, allowing smuggled requests to bypass mitmproxy's capture and event processing.
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 · scopedUpgrade mitmproxy to version 7.0.3 or higher. If using mitmproxy to protect HTTP/1 services, verify that the upgrade is applied and test that smuggled requests are now properly detected and logged.
mitmproxy 7.0.3 or higher
- Ensure you have a backup of your mitmproxy configuration and any custom addons or scripts
- Stop any running mitmproxy instance
- Upgrade mitmproxy using your package manager or pip: pip install --upgrade mitmproxy
- Verify the installed version is 7.0.3 or higher by running: mitmproxy --version
- Restart mitmproxy with your configuration
- Test that your workflows and any custom addons still function correctly
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation2.0 h
- Testing3.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2021-39214 — 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-2021-39214 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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