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Low severityNVD Advisory· Published Oct 12, 2021· Updated May 27, 2025

Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling') in puma

CVE-2021-41136

Description

Puma is a HTTP 1.1 server for Ruby/Rack applications. Prior to versions 5.5.1 and 4.3.9, using puma with a proxy which forwards HTTP header values which contain the LF character could allow HTTP request smugggling. A client could smuggle a request through a proxy, causing the proxy to send a response back to another unknown client. The only proxy which has this behavior, as far as the Puma team is aware of, is Apache Traffic Server. 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 vulnerability was patched in Puma 5.5.1 and 4.3.9. As a workaround, do not use Apache Traffic Server with puma.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
pumaRubyGems
>= 5.0.0, < 5.5.15.5.1
pumaRubyGems
< 4.3.94.3.9

Affected products

98

Patches

Vulnerability mechanics

References

12

News mentions

0

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