OpenBao's System Backend allows Unauthorized Management of the containing Namespace
Summary
A user that is granted namespace management (/sys/namespaces) capabilities within a non-root namespace ("the victim namespace") can abuse special handling of the literal path "root" in namespace path canonicalization to manage the victim namespace itself.
Details
Several endpoints under /sys/namespaces/* accept a namespace path segment that is canonicalized and then appended to the path of the sys mount's containing namespace (set via path prefix or X-Vault-Namespace header) to determine the absolute path of the namespace to operate on.
Given the special namespace path "root" canonicalizes to en empty path (""), when passed as /sys/namespaces/root, the resulting absolute namespace path remains equal to the sys mount's containing namespace. Given ACLs are evaluated before namespace path canonicalization, this allows users with capabilities on /sys/namespaces/root within any given namespace to operate on the namespace itself instead.
Impact
Users that were granted the required capabilities can abuse this vulnerability to:
- Look up
- Delete
- Lock
- Patch custom metadata
against the namespace containing the system backend they can manage sys/namespaces/root in. The exact range of operations that can be performed depends on the specific capabilities granted on said path and any sub-paths such as /api-lock.
Notably, the root namespace is immutable and cannot be modified, deleted or locked, and is thus unaffected. Also note that users can only abuse this vulnerability to operate on the direct parent or "containing" namespace relative to their capabilities, not arbitrary namespaces.
Patch
This will be fixed in OpenBao v2.5.5.
PoC
Start a development server:
bao server -devCreate a namespace:
bao namespace create victimThis will be the namespace we gain unauthorized management of.
Create a policy that allows management of namespaces, _inside_ of the victim namespace.
bao policy write -namespace=victim namespace-management - <<EOF
path "sys/namespaces/*" {
capabilities = ["read", "update", "patch", "delete"]
}
EOFThen create a token with above policy attached:
export BAO_TOKEN=$(bao token create -namespace=victim -policy=namespace-management -field=token)Operate on the victim's namespace using the token, for example by outright deleting it:
bao namespace delete -namespace=victim root