Date: Mon, 25 Jan 2016 11:33:08 -0800 From: Aaron Patterson <tenderlove@...y-lang.org> To: security@...e.de, rubyonrails-security@...glegroups.com, oss-security@...ts.openwall.com, ruby-security-ann@...glegroups.com Subject: [CVE-2015-7577] Nested attributes rejection proc bypass in Active Record. Nested attributes rejection proc bypass in Active Record. There is a vulnerability in how the nested attributes feature in Active Record handles updates in combination with destroy flags when destroying records is disabled. This vulnerability has been assigned the CVE identifier CVE-2015-7577. Versions Affected: 3.1.0 and newer Not affected: 3.0.x and older Fixed Versions: 5.0.0.beta1.1, 184.108.40.206, 220.127.116.11, 18.104.22.168 Impact ------ When using the nested attributes feature in Active Record you can prevent the destruction of associated records by passing the `allow_destroy: false` option to the `accepts_nested_attributes_for` method. However due to a change in the commit [a9b4b5d] the `_destroy` flag prevents the `:reject_if` proc from being called because it assumes that the record will be destroyed anyway. However this isn't true if `:allow_destroy` is false so this leads to changes that would have been rejected being applied to the record. Attackers could use this do things like set attributes to invalid values and to clear all of the attributes amongst other things. The severity will be dependent on how the application has used this feature. All users running an affected release should either upgrade or use one of the workarounds immediately. Releases -------- The FIXED releases are available at the normal locations. Workarounds ----------- If you can't upgrade, please use the following monkey patch in an initializer that is loaded before your application: ``` $ cat config/initializers/nested_attributes_bypass_fix.rb module ActiveRecord module NestedAttributes private def reject_new_record?(association_name, attributes) will_be_destroyed?(association_name, attributes) || call_reject_if(association_name, attributes) end def call_reject_if(association_name, attributes) return false if will_be_destroyed?(association_name, attributes) case callback = self.nested_attributes_options[association_name][:reject_if] when Symbol method(callback).arity == 0 ? send(callback) : send(callback, attributes) when Proc callback.call(attributes) end end def will_be_destroyed?(association_name, attributes) allow_destroy?(association_name) && has_destroy_flag?(attributes) end def allow_destroy?(association_name) self.nested_attributes_options[association_name][:allow_destroy] end end end ``` 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. * 3-2-nested-attributes-reject-if-bypass.patch - Patch for 3.2 series * 4-1-nested-attributes-reject-if-bypass.patch - Patch for 4.1 series * 4-2-nested-attributes-reject-if-bypass.patch - Patch for 4.2 series * 5-0-nested-attributes-reject-if-bypass.patch - Patch for 5.0 series Please note that only the 4.1.x and 4.2.x 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 ------- Thank you to Justin Coyne for reporting the problem and working with us to fix it. : https://github.com/rails/rails/commit/a9b4b5da7c216e4464eeb9dbd0a39ea258d64325 -- Aaron Patterson http://tenderlovemaking.com/ View attachment "3-2-nested-attributes-reject-if-bypass.patch" of type "text/plain" (3820 bytes) View attachment "4-1-nested-attributes-reject-if-bypass.patch" of type "text/plain" (4006 bytes) View attachment "4-2-nested-attributes-reject-if-bypass.patch" of type "text/plain" (4006 bytes) View attachment "5-0-nested-attributes-reject-if-bypass.patch" of type "text/plain" (4008 bytes) Content of type "application/pgp-signature" skipped
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