Headline
CVE-2021-41136
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.
Impact
Prior to puma version 5.5.0, using puma with a proxy which forwards LF characters as line endings could allow HTTP request smuggling. A client could smuggle a request through a proxy, causing the proxy to send a response back to another unknown client.
This behavior (forwarding LF characters as line endings) is very uncommon amongst proxy servers, so we have graded the impact here as "low". Puma is only aware of a single proxy server which has this behavior.
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.
Patches
This vulnerability was patched in Puma 5.5.1 and 4.3.9.
Workarounds
This vulnerability only affects Puma installations without any proxy in front.
Use a proxy which does not forward LF characters as line endings.
Proxies which do not forward LF characters as line endings:
- Nginx
- Apache (>2.4.25)
- Haproxy
- Caddy
- Traefik
Possible Breakage
If you are dealing with legacy clients that want to send LF as a line ending in an HTTP header, this will cause those clients to receive a 400 error.
References
- HTTP Request Smuggling
For more information
If you have any questions or comments about this advisory:
- Open an issue in Puma
- See our security policy
Related news
Gentoo Linux Security Advisory 202208-28 - Multiple vulnerabilities have been discovered in Puma, the worst of which could result in denial of service. Versions less than 5.6.4 are affected.
Red Hat Security Advisory 2022-5498-01 - Red Hat Satellite is a systems management tool for Linux-based infrastructure. It allows for provisioning, remote management, and monitoring of multiple Linux deployments with a single centralized tool. Issues addressed include HTTP request smuggling, buffer overflow, bypass, code execution, cross site scripting, denial of service, heap overflow, information leakage, privilege escalation, remote shell upload, remote SQL injection, and traversal vulnerabilities.
An update is now available for Red Hat Satellite 6.11This content is licensed under the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/). If you distribute this content, or a modified version of it, you must provide attribution to Red Hat Inc. and provide a link to the original. Related CVEs: * CVE-2021-3200: libsolv: heap-based buffer overflow in testcase_read() in src/testcase.c * CVE-2021-3584: foreman: Authenticate remote code execution through Sendmail configuration * CVE-2021-4142: Satellite: Allow unintended SCA certificate to authenticate Candlepin * CVE-2021-21290: netty: Information disclosure via the local system temporary directory * CVE-2021-21295: netty: possible request smuggling in HTTP/2 due missing validation * CVE-2021-21409: netty: Request smuggling via content-length header * CVE-2021-30151: sidekiq: XSS via the queue name of the live-poll feature * CVE-2021-32839: python-sqlparse: ReDoS via regular expression i...
In Puma (RubyGem) before 4.3.4 and 3.12.5, an attacker could smuggle an HTTP response, by using an invalid transfer-encoding header. The problem has been fixed in Puma 3.12.5 and Puma 4.3.4.