CVE-2021-41136: Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling') in puma
First published: Tue Oct 12 2021(Updated: )
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`.
Credit: security-advisories@github.com
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Puma Puma | <=4.3.8 | |
| Puma Puma | >=5.0.0<=5.5.0 | |
| Debian Debian Linux | =10.0 | |
| Debian Debian Linux | =11.0 | |
| debian/puma | <=3.12.0-2+deb10u2<=4.3.8-1 | 3.12.0-2+deb10u3 4.3.8-1+deb11u2 5.6.5-3 5.6.7-1 |
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Reference Links
- https://github.com/puma/puma/commit/acdc3ae571dfae0e045cf09a295280127db65c7f
- https://github.com/puma/puma/security/advisories/GHSA-48w2-rm65-62xx
- https://lists.debian.org/debian-lts-announce/2022/08/msg00015.html
- https://security.gentoo.org/glsa/202208-28
- https://www.debian.org/security/2022/dsa-5146
- https://bugzilla.redhat.com/show_bug.cgi/show_bug.cgi?id=2013497
- https://src.fedoraproject.org/rpms/rubygem-puma
- https://access.redhat.com/errata/RHSA-2022:5498
- https://access.redhat.com/security/cve/cve-2021-41136
- https://bugzilla.redhat.com/show_bug.cgi?id=2013495
- https://security-tracker.debian.org/tracker/CVE-2021-41136
Frequently Asked Questions
What is CVE-2021-41136?
CVE-2021-41136 is a vulnerability in the Puma server that allows HTTP request smuggling.
What is the severity of CVE-2021-41136?
The severity of CVE-2021-41136 is low.
How does CVE-2021-41136 affect Puma?
CVE-2021-41136 affects Puma versions prior to 5.5.1 and 4.3.9.
How can CVE-2021-41136 be exploited?
CVE-2021-41136 can be exploited by using a proxy that forwards HTTP header values containing the LF character.
How can I fix CVE-2021-41136?
To fix CVE-2021-41136, upgrade to Puma version 5.5.1 or 4.3.9, depending on your current version.
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