CVE-2020-8159: Actionpack page caching Arbitrary File Write Vulnerability

CRITICAL
Advisory Identifier: GHSA-mg5p-95m9-rmfp
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CVSS 9.8
CWE-22
Published
Advisory Summary

CVE-2020-8159 is a CRITICAL (CVSS 9.8) arbitrary file write vulnerability (CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')) affecting Actionpack page caching libraries in the RubyGems ecosystem. The issue involves arbitrary file write in actionpack-page_caching gem. Remediation is available by upgrading affected packages to version 1.2.1.

CVE-2020-8159 at a Glance

CVE Identifier CVE-2020-8159
GHSA Identifier GHSA-mg5p-95m9-rmfp
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Affected Product Actionpack page caching
Package Ecosystem RubyGems
Published Date
Last Updated

Security Impact

CVSS: 9.8

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

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2020-8159

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

actionpack-page_caching fixed: 1.2.1 
Upgrade actionpack-page_caching to 1.2.1
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 actionpack-page_caching

How to Check if You Are Affected

To determine whether your application is affected by CVE-2020-8159, inspect your project dependencies for Actionpack page caching:

inspect dependencies for actionpack-page_caching

Analyze the terminal output to locate any version of Actionpack page caching in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.2.1), 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-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'), where the product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. In Actionpack page caching, 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

There is a vulnerability in actionpack_page-caching gem < v1.2.1 that allows an attacker to write arbitrary files to a web server, potentially resulting in remote code execution if the attacker can write unescaped ERB to a view.

CVE-2020-8159 Affected Actionpack page caching Versions

1 component(s)
Fixed Versions:
1.2.1
Product / Package Ecosystem Affected Versions Fixed Version
actionpack-page_caching
gem/actionpack-page_caching
RubyGems
< 1.2.1
1.2.1

References

NVD — CVE-2020-8159 NVD
https://nvd.nist.gov/vuln/detail/CVE-2020-8159
Security Fix Commit FIX COMMIT
https://github.com/rails/actionpack-page_caching/commit/127da70a559bed4fc573fdb4a6d498a7d5815ce2
groups.google.com/forum/ WEB
https://groups.google.com/forum/#!topic/rubyonrails-security/CFRVkEytdP8
lists.debian.org/debian-lts-announce... WEB
https://lists.debian.org/debian-lts-announce/2021/07/msg00019.html

Frequently Asked Questions

What is CVE-2020-8159?
CVE-2020-8159 is a security vulnerability in Actionpack page caching involving Arbitrary file write in actionpack-page_caching gem under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal').
Which Actionpack page caching versions are affected?
Affected versions include releases prior to 1.2.1 across affected packages: actionpack-page_caching.
What version fixes CVE-2020-8159?
Upgrading to 1.2.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is actionpack-page_caching affected?
Yes, actionpack-page_caching is affected in releases prior to 1.2.1. Upgrade your dependency to 1.2.1 or later.
What is the CVSS score of CVE-2020-8159?
CVE-2020-8159 has a CVSS v3.1 base score of 9.8 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2020-8159?
CVE-2020-8159 is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') (The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.).
How can I check RubyGems dependencies for CVE-2020-8159?
Run the dependency tree command: 'inspect dependencies for actionpack-page_caching'. 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-mg5p-95m9-rmfp",
  "modified" : "2021-07-26T21:16:26Z",
  "published" : "2020-05-13T16:28:46Z",
  "aliases" : [ "CVE-2020-8159" ],
  "summary" : "Arbitrary file write in actionpack-page_caching gem",
  "details" : "There is a vulnerability in actionpack_page-caching gem < v1.2.1 that allows an attacker to write arbitrary files to a web server, potentially resulting in remote code execution if the attacker can write unescaped ERB to a view.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "actionpack-page_caching"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.2.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-8159"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rails/actionpack-page_caching/commit/127da70a559bed4fc573fdb4a6d498a7d5815ce2"
  }, {
    "type" : "WEB",
    "url" : "https://groups.google.com/forum/#!topic/rubyonrails-security/CFRVkEytdP8"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2021/07/msg00019.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-05-13T16:28:30Z",
    "nvd_published_at" : "2020-05-12T13:15:00Z"
  }
}