This seems counter-intuitive at first glance, but let me cook.
One of the problems with Anubis is that the rule matching is super
deterministic. This means that attackers can figure out what patterns
they are hitting and change things to bypass them.
The randInt function lets you have rulesets behave nondeterministically.
This is a very easy way to hang yourself, but can be great to
psychologically mess with scraper operators. Consider this rule:
```yaml
- name: deny-lightpanda-sometimes
action: DENY
expression:
all:
- userAgent.matches("LightPanda")
- randInt(16) >= 4
```
It would match about 75% of the time.
Signed-off-by: Xe Iaso <me@xeiaso.net>
* feat(lib/policy): add support for CEL checkers
This adds the ability for administrators to use Common Expression
Language[0] (CEL) for more advanced check logic than Anubis previously
offered.
These can be as simple as:
```yaml
- name: allow-api-routes
action: ALLOW
expression:
and:
- '!(method == "HEAD" || method == "GET")'
- path.startsWith("/api/")
```
or get as complicated as:
```yaml
- name: allow-git-clients
action: ALLOW
expression:
and:
- userAgent.startsWith("git/") || userAgent.contains("libgit") || userAgent.startsWith("go-git") || userAgent.startsWith("JGit/") || userAgent.startsWith("JGit-")
- >
"Git-Protocol" in headers && headers["Git-Protocol"] == "version=2"
```
Internally these are compiled and evaluated with cel-go[1]. This also
leaves room for extensibility should that be desired in the future. This
will intersect with #338 and eventually intersect with TLS fingerprints
as in #337.
[0]: https://cel.dev/
[1]: https://github.com/google/cel-go
Signed-off-by: Xe Iaso <me@xeiaso.net>
* feat(data/apps): add API route allow rule for non-HEAD/GET
Signed-off-by: Xe Iaso <me@xeiaso.net>
* docs: document expression syntax
Signed-off-by: Xe Iaso <me@xeiaso.net>
* fix: fixes in review
Signed-off-by: Xe Iaso <me@xeiaso.net>
---------
Signed-off-by: Xe Iaso <me@xeiaso.net>
Closes#372
Fun YAML fact of the day:
What is the difference between how these two expressions are parsed?
```yaml
foo: >
bar
```
```yaml
foo: >-
bar
```
They are invisible in yaml, but when you evaluate them to JSON the
difference is obvious:
```json
{
"foo": "bar\n"
}
```
```json
{
"foo": "bar"
}
```
User-Agent strings, URL path values, and HTTP headers _do_ end in
newlines in HTTP/1.1 wire form, but that newline is usually stripped
before the server actually handles it. Also HTTP/2 is a thing and does
not terminate header values with newlines.
This change makes Anubis more aggressively detect mistaken uses of the
yaml `>` operator and nudges the user into using the yaml `>-` operator
which does not append the trailing newline.
I had honestly forgotten about this YAML behavior because it wasn't
relevant for so long. Oops! Glad I released a beta.
Whenever you get into this state, Anubis will throw a config parsing
error and then give you a message hinting at the folly of your ways.
```
config.Bot: regular expression ends with newline (try >- instead of > in yaml)
```
Big thanks to https://yaml-multiline.info, this helped me realize my
folly instantly.
@aiverson, this is official permission to say "told you so".
Signed-off-by: Xe Iaso <me@xeiaso.net>
* feat(config): support importing bot policy snippets
This changes the grammar of the Anubis bot policy config to allow
importing from internal shared rules or external rules on the
filesystem.
This lets you create a file at `/data/policies/block-evilbot.yaml` and
then import it with:
```yaml
bots:
- import: /data/policies/block-evilbot.yaml
```
This also explodes the default policy file into a bunch of composable
snippets.
Thank you @Aibrew for your example gitea Atom / RSS feed rules!
Signed-off-by: Xe Iaso <me@xeiaso.net>
* fix(data): update botPolicies.json to use imports
Signed-off-by: Xe Iaso <me@xeiaso.net>
* fix(cmd/anubis): extract bot policies with --extract-resources
This allows a user that doesn't have anything but the Anubis binary to
figure out what the default configuration does.
* docs(data/botPolices.yaml): document import syntax in-line
Signed-off-by: Xe Iaso <me@xeiaso.net>
* fix(lib/policy): better test importing from JSON snippets
Signed-off-by: Xe Iaso <me@xeiaso.net>
* docs(admin): Add import syntax documentation
This documents the import syntax and is based on the block comment at
the top of the default bot policy file.
* docs(changelog): add note about importing snippets
Signed-off-by: Xe Iaso <me@xeiaso.net>
* style(lib/policy/config): use an error value instead of an inline error
Signed-off-by: Xe Iaso <me@xeiaso.net>
---------
Signed-off-by: Xe Iaso <me@xeiaso.net>
