PumaApplication
CVE-2020-11077
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 · uneditedIn Puma (RubyGem) before 4.3.5 and 3.12.6, a client could smuggle a request through a proxy, causing the proxy to send a response back to another unknown client. If the proxy uses persistent connections and the client adds another request in via HTTP pipelining, the proxy may mistake it as the first request's body. Puma, however, would see it as two requests, and when processing the second request, send back a response that the proxy does not expect. If the proxy has reused the persistent connection to Puma to send another request for a different client, the second response from the first client will be sent to the second client. This is a similar but different vulnerability from CVE-2020-11076. The problem has been fixed in Puma 3.12.6 and Puma 4.3.5.
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 confidenceHTTP request smuggling vulnerability in Puma where a client can smuggle requests through a proxy using HTTP pipelining. The proxy may misidentify pipelined requests as the first request's body, causing Puma to send responses back to the proxy that get routed to the wrong client when persistent connections are reused.
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
PumaApplication
>= 3.0.0, < 3.12.6>= 4.0.0, < 4.3.5
FedoraOperating system
= 33
Debian LinuxOperating system
= 9.0= 15.1= 15.2CVSS 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
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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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Identify Puma versionRun `gem list puma` or check your Gemfile.lock for the puma gem version, or inspect the running process with `ps aux | grep puma` and check loaded librariesAffected if The Puma version is 3.0.0 through 3.12.5, or 4.0.0 through 4.3.4 (any version >= 3.0.0 and < 3.12.6, or >= 4.0.0 and < 4.3.5)
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Confirm Puma is exposed via a proxyReview your infrastructure architecture to determine if a reverse proxy (nginx, Apache, HAProxy, cloud load balancer, or similar) sits in front of the Puma server and forwards HTTP requests to itAffected if A proxy forwards requests to Puma and reuses persistent (keep-alive) connections to pipe multiple client requests together
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Verify HTTP pipelining is possibleCheck if the proxy configuration permits HTTP pipelining and persistent connections to the backend Puma server. Inspect proxy logs or configuration for keep-alive or pipeline settingsAffected if The proxy maintains persistent connections to Puma and forwards pipelined requests without buffering the full request body first
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Check for unusual request routingReview application and proxy access logs for suspicious patterns: unexpected response sizes, mismatched request/response pairs, or evidence of one client receiving another client's responseAffected if Logs show responses being returned to the wrong client, or request boundaries appearing to be misaligned between the proxy and Puma
You are affected if your Puma version falls in the vulnerable range (3.0.0 to < 3.12.6 or 4.0.0 to < 4.3.5) AND you run Puma behind a proxy that forwards pipelined requests over persistent connections.
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.
From vendor data3.12.64.3.5
Upgrade Puma to version 3.12.6 or 4.3.5 or later to patch the request smuggling vulnerability.
Fix this in Puma
Scoped from the published advisory
- Consultation1.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-11077 — 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-2020-11077 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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