CVE-2020-15237.yml

---
gem: shrine
cve: 2020-15237
ghsa: 5jjv-x4fq-qjwp
url: https://github.com/shrinerb/shrine/security/advisories/GHSA-5jjv-x4fq-qjwp
date: 2020-10-05
title: Possible timing attack in derivation_endpoint
description: |
  ### Impact

  When using the `derivation_endpoint` plugin, it's possible for the attacker to use a timing attack
  to guess the signature of the derivation URL.

  ### Patches

  The problem has been fixed by comparing sent and calculated signature in constant time, using
  `Rack::Utils.secure_compare`. Users using the `derivation_endpoint` plugin are urged to upgrade
  to Shrine 3.3.0 or greater.

  ### Workarounds

  Users of older Shrine versions can apply the following monkey-patch after loading the `derivation_endpoint` plugin:

  ```rb
  class Shrine
    class UrlSigner
      def verify_signature(string, signature)
        if signature.nil?
          fail InvalidSignature, "missing \"signature\" param"
        elsif !Rack::Utils.secure_compare(signature, generate_signature(string))
          fail InvalidSignature, "provided signature does not match the calculated signature"
        end
      end
    end
  end
  ```

  ### References

  You can read more about timing attacks [here](https://en.wikipedia.org/wiki/Timing_attack).
cvss_v3: 5.9
patched_versions:
  - ">= 3.3.0"