GHSA-48W2-RM65-62XX

Vulnerability from github – Published: 2021-10-12 17:53 – Updated: 2025-05-27 15:16
VLAI?
Summary
Puma with proxy which forwards LF characters as line endings could allow HTTP request smuggling
Details

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

For more information

If you have any questions or comments about this advisory:

Severity ?
3.7 (Low)
CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "puma"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "5.0.0"
            },
            {
              "fixed": "5.5.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "RubyGems",
        "name": "puma"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.3.9"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2021-41136"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-444"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2021-10-12T17:06:36Z",
    "nvd_published_at": "2021-10-12T16:15:00Z",
    "severity": "LOW"
  },
  "details": "### Impact\n\nPrior 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.\n\nThis 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.\n\nIf the proxy uses persistent connections and the client adds another request in via HTTP pipelining, the proxy may mistake it as the first request\u0027s 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.\n\n### Patches\n\nThis vulnerability was patched in Puma 5.5.1 and 4.3.9.\n\n### Workarounds\n\nThis vulnerability only affects Puma installations without any proxy in front.\n\nUse a proxy which does not forward LF characters as line endings.\n\nProxies which do not forward LF characters as line endings:\n\n* Nginx\n* Apache (\u003e2.4.25)\n* Haproxy\n* Caddy\n* Traefik\n\n### Possible Breakage\n\nIf you are [dealing with legacy clients that want to send `LF` as a line ending](https://stackoverflow.com/questions/43574428/have-apache-accept-lf-vs-crlf-in-request-headers) in an HTTP header, this will cause those clients to receive a `400` error.\n\n### References\n\n* [HTTP Request Smuggling](https://portswigger.net/web-security/request-smuggling)\n\n### For more information\n\nIf you have any questions or comments about this advisory:\n\n* Open an issue in [Puma](https://github.com/puma/puma)\n* See our [security policy](https://github.com/puma/puma/security/policy)",
  "id": "GHSA-48w2-rm65-62xx",
  "modified": "2025-05-27T15:16:14Z",
  "published": "2021-10-12T17:53:00Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/puma/puma/security/advisories/GHSA-48w2-rm65-62xx"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-41136"
    },
    {
      "type": "WEB",
      "url": "https://github.com/puma/puma/commit/436c71807f00e07070902a03f79fd3e130eb6b18"
    },
    {
      "type": "WEB",
      "url": "https://github.com/puma/puma/commit/acdc3ae571dfae0e045cf09a295280127db65c7f"
    },
    {
      "type": "WEB",
      "url": "https://github.com/puma/puma/commit/fb6ad8f8013ab5cdbb2f444cbfabd0b4fde71139"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/puma/puma"
    },
    {
      "type": "WEB",
      "url": "https://github.com/puma/puma/releases/tag/v4.3.9"
    },
    {
      "type": "WEB",
      "url": "https://github.com/puma/puma/releases/tag/v5.5.1"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/puma/CVE-2021-41136.yml"
    },
    {
      "type": "WEB",
      "url": "https://lists.debian.org/debian-lts-announce/2022/08/msg00015.html"
    },
    {
      "type": "WEB",
      "url": "https://security.gentoo.org/glsa/202208-28"
    },
    {
      "type": "WEB",
      "url": "https://www.debian.org/security/2022/dsa-5146"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Puma with proxy which forwards LF characters as line endings could allow HTTP request smuggling"
}


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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Detection rules are retrieved from Rulezet.