An information exposure vulnerability in Canonical MAAS prior to versions 3.4.10, 3.5.14, 3.6.5, 3.7.3, and 3.8.0 allows an unauthenticated attacker to retrieve the RPC secret in plaintext via the vendor data metadata endpoint. If a target machine was deployed with the 'register as rack' option enabled, an attacker who obtains or infers the machine's system ID can query the preseed/metadata server to leak the secret.
https://github.com/canonical/maas/commit/ead659f70224538517c80478c3fd8c9e730aae79
https://github.com/canonical/maas/commit/a9486ad0cc90f4571142c1bea13f02d1361cb31e
https://github.com/canonical/maas/commit/8489979d64b0e7f124e7cef66d02b21263918f9b
https://github.com/canonical/maas/commit/65e89c05970f4514f9e6de043c2779017b43ad9d
https://github.com/canonical/maas/commit/3864ef9dca54e36e3d34d18233b87666b8ee1dc8