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Threat analysis for the federated star activity

Technical Background

Control Flow

sequenceDiagram
    participant fs as foreign_repository_server
    participant os as our_repository_server

    fs ->> os: post /api/activitypub/repository-id/1/inbox {Start-Activity}
    activate os
    os ->> os: validate request inputs
    activate repository
    os ->> repository: validate
    repository ->> repository: search for reop with object-id
    deactivate repository
    activate person
    os ->> person: validate
    person ->> person: search for ser with actor-id
    person ->> fs: get /api/activitypub/user-id/{id from actor}
    person ->> person: create user from response
    deactivate person
    os ->> repository: execute star action
    os -->> fs: 200 ok
    deactivate os

Data transfered

# edn notation
{@context [
    "as":    "https://www.w3.org/ns/activitystreams#",
    "forge": "https://forgefed.org/ns#",],
  ::as/id "https://repo.prod.meissa.de/api/v1/activitypub/user-id/1/outbox/12345",
  ::as/type "Star",
  ::forge/source "forgejo",
  ::as/actor "https://repo.prod.meissa.de/api/v1/activitypub/user-id/1",
  ::as/object "https://codeberg.org/api/v1/activitypub/repository-id/12"
}

# json notation
{"id": "https://repo.prod.meissa.de/api/v1/activitypub/user-id/1/outbox/12345",
  "type": "Star",
  "source": "forgejo",
  "actor": "https://repo.prod.meissa.de/api/v1/activitypub/user-id/1",
  "object": "https://codeberg.org/api/v1/activitypub/repository-id/1"
}

Data Flow

flowchart TD
    A(User) --> |stars a federated repository| B(foreign repository server)
    B --> |Star Activity| C(our repository server)
    C --> |get repository localy| D(our repos database)
	C --> |get Person Actor| B
    C --> |create federated user localy| D
    C --> |add star to repo localy| D

Analysis

Assets

  1. Service Availability: The availability of our or foreign servers.
  2. Reputation: Our standing against freinds and others.

Actors

  1. Script Kiddies: Boored teens, willing to do some illigal without deep knowlege of tech details but broad knowlege across internet discussions. Able to do some bash / python scripting.
  2. Experienced Hacker: Hacker with deep knowlege.
  3. OpenSource Promoter:

Threat

  1. Script Kiddi sends a Star Activity containing an attack actor url http://attacked.target/very/special/path in place of actor. Our repository server sends an get Person Actor request to this url. The attacked target gets DenialdOffServices. We loose CPU & reputation.
  2. Experienced hacker sends a Star Activity containing an actor url pointing to an evil forgejo instance. Our repository server sends an get Person Actor request to this instance and get a person having sth. like ; drop database; in its name. If our server tries to create a new user out of this persion, the db might be droped.
  3. OpenSource Promoter sends Star Activities having not authorized Person Actors. The Actors listed as stargazer migth get angry about this, we loose reputation.
  4. Experienced Hacker records activities sent and replays some of them. Without order of activities (i.e. timestamp) we can not decide wether we should execute the activity again. If activity is Unstar Activity we might loose stars.
  5. Experienced Hacker records activities sends a massive amount of activities which leads to new user storage. Our instance might get off service.

DREAD-Score

Threat Damage Reproducibility Exploitability Affected Users Discoverability Mitigations
1. ... tbd
2. ... tbd

Bewertet wird mit Schulnoten von 1 - 6

  • Damage – wie groß wäre der Schaden, wenn der Angriff erfolgreich ist? 6 ist ein sehr schlimmer Schaden.
  • Reproducibility – wie einfach wäre der Angriff reproduzierbar? 6 ist sehr einfach zu reproduzieren.
  • Exploitability – wieviel Zeit, Aufwand und Erfahrung sind notwendig, um die Bedrohung auszunutzen? 6 ist sehr einfach zu machen.
  • Affected Users – wenn eine Bedrohung ausgenutzt werden würde, wieviel Prozent der Benutzer wären betroffen?
  • Discoverability – Wie einfach lässt sich ein Angriff entdecken? Muss der Angreifer Strafverfolgung erwarten? 6 ist sehr schwer zu entdecken / ist gar nicht illegal

Reference