==================================================================== CERT-Renater Note d'Information No. 2020/VULN290 _____________________________________________________________________ DATE : 20/05/2020 HARDWARE PLATFORM(S): / OPERATING SYSTEM(S): Systems running Rails versions prior to 5.2.4.3, 6.0.3.1, 4.2.11.2. ===================================================================== https://groups.google.com/forum/#!topic/rubyonrails-security/PjU3946mreQ https://groups.google.com/forum/#!topic/rubyonrails-security/f6ioe4sdpbY https://groups.google.com/forum/#!topic/rubyonrails-security/bv6fW4S0Y1c https://groups.google.com/forum/#!topic/rubyonrails-security/NOjKiGeXUgw https://groups.google.com/forum/#!topic/rubyonrails-security/x9DixQDG9a0 https://groups.google.com/forum/#!topic/rubyonrails-security/hWuKcHyoKh0 _____________________________________________________________________ Circumvention of file size limits in ActiveStorage There is a vulnerability in ActiveStorage's S3 adapter that allows the Content-Length of a direct file upload to be modified by an end user. This vulnerability has been assigned the CVE identifier CVE-2020-8162. Versions Affected: rails < 5.2.4.2, rails < 6.0.3.1 Not affected: Applications that do not use the direct upload functionality of the ActiveStorage S3 adapter. Fixed Versions: rails >= 5.2.4.3, rails >= 6.0.3.1 Impact ------ Utilizing this vulnerability, an attacker can control the Content-Length of an S3 direct upload URL without receiving a new signature from the server. This could be used to bypass controls in place on the server to limit upload size. Releases -------- Rails 5.2.4.3 and 6.0.3.1 are available on RubyGems. Workarounds ----------- This is a low-severity security issue. As such, no workaround is necessarily until such time as the application can be upgraded. Patches ------- For developers who are not able to immediately patch their applications, we are including the following patches for Rails 6.0.3 and Rails 5.2.4.2. * 5-2-activestorage-s3-adapter.patch * 6-0-activestorage-s3-adapter.patch Credits ------- Thanks to Travis Pew (@travisp) for reporting this issue via our HackerOne bug bounty program and providing a patch. _____________________________________________________________________ # Possible Strong Parameters Bypass in ActionPack There is a strong parameters bypass vector in ActionPack. This vulnerability has been assigned the CVE identifier CVE-2020-8164. Versions Affected: rails <= 6.0.3 Not affected: rails < 4.0.0 Fixed Versions: rails >= 5.2.4.3, rails >= 6.0.3.1 Impact ------ In some cases user supplied information can be inadvertently leaked from Strong Parameters. Specifically the return value of `each`, or `each_value`, or `each_pair` will return the underlying "untrusted" hash of data that was read from the parameters. Applications that use this return value may be inadvertently use untrusted user input. Impacted code will look something like this: ``` def update # Attacker has included the parameter: `{ is_admin: true }` User.update(clean_up_params) end def clean_up_params params.each { |k, v| SomeModel.check(v) if k == :name } end ``` Note the mistaken use of `each` in the `clean_up_params` method in the above example. Releases -------- The 5.2.4.3 and 6.0.3.1 releases are available at the normal locations. Workarounds ----------- Do not use the return values of `each`, `each_value`, or `each_pair` in your application. Patches ------- To aid users who aren't able to upgrade immediately we have provided patches for the two supported release series. They are in git-am format and consist of a single changeset. * 5-2-strong-params.patch - Patch for 5.2 series * 6-0-strong-params.patch - Patch for 6.0 series Please note that only the 6.0 and 5.2 series are supported at present. Users of earlier unsupported releases are advised to upgrade as soon as possible as we cannot guarantee the continued availability of security fixes for unsupported releases. Credits ------- Thanks to Achilleas (@abuisman) for reporting this issue via our HackerOne bug bounty program _____________________________________________________________________ Potentially unintended unmarshalling of user-provided objects in MemCacheStore and RedisCacheStore There is potentially unexpected behaviour in the MemCacheStore and RedisCacheStore where, when untrusted user input is written to the cache store using the `raw: true` parameter, re-reading the result from the cache can evaluate the user input as a Marshalled object instead of plain text. Vulnerable code looks like: ``` data = cache.fetch("demo", raw: true) { untrusted_string } ``` This vulnerability has been assigned the CVE identifier CVE-2020-8165. Versions Affected: rails < 5.2.5, rails < 6.0.4 Not affected: Applications not using MemCacheStoer or RedisCacheStore. Applications that do not use the `raw` option when storing untrusted user input. Fixed Versions: rails >= 5.2.4.3, rails >= 6.0.3.1 Impact ------ Unmarshalling of untrusted user input can have impact up to and including RCE. At a minimum, this vulnerability allows an attacker to inject untrusted Ruby objects into a web application. In addition to upgrading to the latest versions of Rails, developers should ensure that whenever they are calling `Rails.cache.fetch` they are using consistent values of the `raw` parameter for both reading and writing, especially in the case of the RedisCacheStore which does not, prior to these changes, detect if data was serialized using the raw option upon deserialization. Releases -------- The fixed releases are available on RubyGems. Workarounds ----------- It is recommended that application developers apply the suggested patch or upgrade to the latest release as soon as possible. If this is not possible, we recommend ensuring that all user-provided strings cached using the `raw` argument should be double-checked to ensure that they conform to the expected format. Patches ------- For developers who are not able to immediately patch their applications, we are including the following patches for Rails 6.0.3 and Rails 5.2.4.2. * 5-2-cache-storage.patch - Patch for 5.2 series * 6-0-cache-storage.patch - Patch for 6.0 series Credits ------- Thank you to Dylan Thacker-Smith for reporting this vulnerability via our HackerOne program and providing a comprehensive set of patches. _____________________________________________________________________ Ability to forge per-form CSRF tokens given a global CSRF token It is possible to possible to, given a global CSRF token such as the one present in the authenticity_token meta tag, forge a per-form CSRF token for any action for that session. This vulnerability has been assigned the CVE identifier CVE-2020-8166. Versions Affected: rails < 5.2.5, rails < 6.0.4 Not affected: Applications without existing HTML injection vulnerabilities. Fixed Versions: rails >= 5.2.4.3, rails >= 6.0.3.1 Impact ------ Given the ability to extract the global CSRF token, an attacker would be able to construct a per-form CSRF token for that session. Releases -------- The fixed releases are available on RubyGems. Workarounds ----------- This is a low-severity security issue. As such, no workaround is necessarily until such time as the application can be upgraded. Patches ------- For developers who are not able to immediately patch their applications, we are including the following patches for Rails 6.0.3 and Rails 5.2.4.2. * 5-2-per-form-csrf.patch - Patch for 5.2 series * 6-0-per-form-csrf.patch - Patch for 6.0 series Credits ------- Thanks to https://hackerone.com/jregele for reporting this issue via our HackerOne bug bounty program. _____________________________________________________________________ CSRF Vulnerability in rails-ujs There is an vulnerability in rails-ujs that allows attackers to send CSRF tokens to wrong domains. This vulnerability has been assigned the CVE identifier CVE-2020-8167. Versions Affected: rails <= 6.0.3 Not affected: Applications which don't use rails-ujs. Fixed Versions: rails >= 5.2.4.3, rails >= 6.0.3.1 Impact ------ This is a regression of CVE-2015-1840. In the scenario where an attacker might be able to control the href attribute of an anchor tag or the action attribute of a form tag that will trigger a POST action, the attacker can set the href or action to a cross-origin URL, and the CSRF token will be sent. Releases -------- The FIXED releases are available at the normal locations. Workarounds ----------- To work around this problem, change code that allows users to control the href attribute of an anchor tag or the action attribute of a form tag to filter the user parameters. For example, code like this: link_to params to code like this: link_to filtered_params def filtered_params # Filter just the parameters that you trust end Patches ------- To aid users who aren't able to upgrade immediately we have provided patches for the supported release series. They are in git-am format and consist of a single changeset. * 5-2-rails-ujs.patch - Patch for 5.2 series * 6-0-rails-ujs.patch - Patch for 6.0 series Credits ------- Thanks to Ben Toews of GitHub for reporting the vulnerability to us. _____________________________________________________________________ Potential remote code execution of user-provided local names in Rails < 5.0.1 There was a vulnerability in versions of Rails prior to 5.0.1 that would allow an attacker who controlled the `locals` argument of a `render` call. This vulnerability has been assigned the CVE identifier CVE-2020-8163. Versions Affected: rails < 5.0.1 Not affected: Applications that do not allow users to control the names of locals. Fixed Versions: 4.2.11.2 Impact ------ In the scenario where an attacker might be able to control the name of a local passed into `render`, they can acheive remote code execution. Releases -------- Users of Rails 5.0 should upgrade to a version >= 5.0.1. This release is already available on RubyGems. Workarounds ----------- Until such time as the patch can be applied, application developers should ensure that all user-provided local names are alphanumeric. Patches ------- As mentioned above, we are releasing the following patch that should apply cleanly to all releases prior to 5.0.1. * 4-2-local-variable-restriction.patch Credits ------- Thanks to Marc Slemko for reporting this issue via our HackerOne bug bounty program. ========================================================= + CERT-RENATER | tel : 01-53-94-20-44 + + 23/25 Rue Daviel | fax : 01-53-94-20-41 + + 75013 Paris | email:cert@support.renater.fr + =========================================================