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`.
This vulnerability carries a LOW severity rating with a CVSS v3.1 score of 3.7, indicating it can be exploited remotely over the network but requires specific conditions to be met though user interaction is required requiring only low-level privileges . The vulnerability impacts limited data confidentiality, limited integrity, for affected systems. Impacting 2 products from puma, from debian organizations running these solutions should prioritize assessment and patching.
Reported in 2021, this vulnerability emerged during an era marked by increased sophistication in supply chain attacks, cloud infrastructure vulnerabilities, and software-as-a-service (SaaS) security challenges. Security practices during this period emphasized zero-trust architectures, container security, and API protection.
2021-10-12T16:15:07.630
2025-05-27T16:15:21.677
Modified
CVSSv3.1: 3.7 (LOW)
AV:N/AC:H/Au:S/C:P/I:P/A:N
3.9
4.9
| Type | Vendor | Product | Version/Range | Vulnerable? |
|---|---|---|---|---|
| Application | puma | puma | ≤ 4.3.8 | Yes |
| Application | puma | puma | ≤ 5.5.0 | Yes |
| Operating System | debian | debian_linux | 10.0 | Yes |
| Operating System | debian | debian_linux | 11.0 | Yes |
SecUtils normalizes and enriches National Vulnerability Database (NVD) records by standardizing vendor and product identifiers, aggregating vulnerability metadata from both NVD and MITRE sources, and providing structured context for security teams. For puma's affected products, we extract Common Platform Enumeration (CPE) data, Common Weakness Enumeration (CWE) classifications, CVSS severity metrics, and reference data to enable rapid vulnerability prioritization and asset correlation. This record contains no exploit code, proof-of-concept instructions, or attack methodologies—only defensive intelligence necessary for patch management, risk assessment, and security operations.