Vulnerability in OpenZFS that disrupts access control in FreeBSD

In added downward API support (simultaneously with this in OpenZFS code supporting the FreeBSD OS has revealed a critical vulnerability (CVE-2020-24717), leading to a violation of access rights processing. The essence of the problem is that rights set for the group were processed as rights for the file owner. The issue has been closed in the update OpenZFS 2.0.0-rc1. The fix added up to translation of the FreeBSD HEAD codebase to OpenZFS.

The problem was caused by the fact that all Access Control List (ACL) entries set for the group owner (group@) and regular groups (group:) were delegated to the current user.
For example, the access mode 0770 (write allowed only for group members) was processed as 0777 (write allowed for all users). A similar situation was observed with ACLs, for instance, the following ACL became equivalent to permissions 0777, as the group member check for builtin_administrators returned True.

# owner: root
# group: wheel
group:builtin_administrators:rwxpDdaARWcCos:——-:allow

Additionally, another issue has been identified in the OpenZFS port for FreeBSD regarding providing rights to change into a directory (cd), regardless of the execution flag state for directories. Entering a directory was possible even when explicitly denied through ACL ('deny — execute')

Source: opennet.ru

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