CVE-2020-5247: Puma HTTP Response Splitting Vulnerability

MODERATE
Advisory Identifier: GHSA-84j7-475p-hp8v
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CVSS 6.5
CWE-113
Published
Advisory Summary

CVE-2020-5247 is a MODERATE (CVSS 6.5) http response splitting vulnerability (CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')) affecting Puma libraries in the RubyGems ecosystem. The issue involves http response splitting in puma. Remediation is available by upgrading affected packages to version 3.12.4, 4.3.3.

CVE-2020-5247 at a Glance

CVE Identifier CVE-2020-5247
GHSA Identifier GHSA-84j7-475p-hp8v
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')
Affected Product Puma
Package Ecosystem RubyGems
Published Date
Last Updated

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction Required (UI:R)
Scope Changed (S:C)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability Low (A:L)

How to Fix CVE-2020-5247

To remediate this vulnerability, upgrade all affected Puma dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

puma fixed: 3.12.4 
Upgrade puma to 3.12.4
puma fixed: 4.3.3 
Upgrade puma to 4.3.3
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for puma

How to Check if You Are Affected

To determine whether your application is affected by CVE-2020-5247, inspect your project dependencies for Puma:

inspect dependencies for puma

Analyze the terminal output to locate any version of Puma in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.12.4), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting'), where the product receives data from an http agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes cr and lf characters before the data is included in outgoing http headers. In Puma, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

In Puma (RubyGem) before 4.3.2 and 3.12.3, if an application using Puma allows untrusted input in a response header, an attacker can use newline characters (i.e. `CR`, `LF` or`/r`, `/n`) to end the header and inject malicious content, such as additional headers or an entirely new response body. This vulnerability is known as HTTP Response Splitting. While not an attack in itself, response splitting is a vector for several other attacks, such as cross-site scripting (XSS). This is related to CVE-2019-16254, which fixed this vulnerability for the WEBrick Ruby web server. This has been fixed in versions 4.3.2 and 3.12.3 by checking all headers for line endings and rejecting headers with those characters.

CVE-2020-5247 Affected Puma Versions

2 component(s)
Fixed Versions:
3.12.44.3.3
Product / Package Ecosystem Affected Versions Fixed Version
puma
gem/puma
RubyGems
< 3.12.4
3.12.4
puma
gem/puma
RubyGems
≥ 4.0.0
< 4.3.3
4.3.3

References

GitHub Advisory / Wiki ADVISORY
https://github.com/puma/puma/security/advisories/GHSA-84j7-475p-hp8v
NVD — CVE-2020-5247 NVD
https://nvd.nist.gov/vuln/detail/CVE-2020-5247
Security Fix Commit FIX COMMIT
https://github.com/puma/puma/commit/c36491756f68a9d6a8b3a49e7e5eb07fe6f1332f
Puma Source Repository REPOSITORY
https://github.com/puma/puma
Puma Source Repository REPOSITORY
https://github.com/rubysec/ruby-advisory-db/blob/master/gems/puma/CVE-2020-5247.yml
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2022/05/msg00034.html
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/BMJ3CGZ3DLBJ5WUUKMI5ZFXFJQMXJZIK
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/DIHVO3CQMU7BZC7FCTSRJ33YDNS3GFPK
lists.fedoraproject.org/archives/list/packa... WEB
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NJ3LL5F5QADB6LM46GXZETREAKZMQNRD
owasp.org/www-community/attac... WEB
https://owasp.org/www-community/attacks/HTTP_Response_Splitting
www.ruby-lang.org/en/news/2019/10/01/... WEB
https://www.ruby-lang.org/en/news/2019/10/01/http-response-splitting-in-webrick-cve-2019-16254

Frequently Asked Questions

What is CVE-2020-5247?
CVE-2020-5247 is a security vulnerability in Puma involving HTTP Response Splitting in Puma under CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting').
Which Puma versions are affected?
Affected versions include releases prior to 3.12.4, 4.3.3 across affected packages: puma.
What version fixes CVE-2020-5247?
Upgrading to 3.12.4, 4.3.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is puma affected?
Yes, puma is affected in releases prior to 3.12.4, 4.3.3. Upgrade your dependency to 3.12.4, 4.3.3 or later.
What is the CVSS score of CVE-2020-5247?
CVE-2020-5247 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L.
What CWE is associated with CVE-2020-5247?
CVE-2020-5247 is classified under CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') (The product receives data from an HTTP agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes CR and LF characters before the data is included in outgoing HTTP headers.).
How can I check RubyGems dependencies for CVE-2020-5247?
Run the dependency tree command: 'inspect dependencies for puma'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-84j7-475p-hp8v",
  "modified" : "2023-05-16T16:16:12Z",
  "published" : "2020-02-28T16:53:55Z",
  "aliases" : [ "CVE-2020-5247" ],
  "summary" : "HTTP Response Splitting in Puma",
  "details" : "In Puma (RubyGem) before 4.3.2 and 3.12.3, if an application using Puma allows untrusted input in a response header, an attacker can use newline characters (i.e. `CR`, `LF` or`/r`, `/n`) to end the header and inject malicious content, such as additional headers or an entirely new response body. This vulnerability is known as HTTP Response Splitting.\n\nWhile not an attack in itself, response splitting is a vector for several other attacks, such as cross-site scripting (XSS).\n\nThis is related to CVE-2019-16254, which fixed this vulnerability for the WEBrick Ruby web server.\n\nThis has been fixed in versions 4.3.2 and 3.12.3 by checking all headers for line endings and rejecting headers with those characters.  ",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L"
  } ],
  "affected" : [ {
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      "ecosystem" : "RubyGems",
      "name" : "puma"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.12.4"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "< 3.12.3"
    }
  }, {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "puma"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      }, {
        "fixed" : "4.3.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "< 4.3.2"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/puma/puma/security/advisories/GHSA-84j7-475p-hp8v"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-5247"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/puma/puma/commit/c36491756f68a9d6a8b3a49e7e5eb07fe6f1332f"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/puma/puma"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/puma/CVE-2020-5247.yml"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2022/05/msg00034.html"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/BMJ3CGZ3DLBJ5WUUKMI5ZFXFJQMXJZIK"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/DIHVO3CQMU7BZC7FCTSRJ33YDNS3GFPK"
  }, {
    "type" : "WEB",
    "url" : "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NJ3LL5F5QADB6LM46GXZETREAKZMQNRD"
  }, {
    "type" : "WEB",
    "url" : "https://owasp.org/www-community/attacks/HTTP_Response_Splitting"
  }, {
    "type" : "WEB",
    "url" : "https://www.ruby-lang.org/en/news/2019/10/01/http-response-splitting-in-webrick-cve-2019-16254"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-113" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-02-28T16:50:49Z",
    "nvd_published_at" : "2020-02-28T17:15:00Z"
  }
}