Today I Learned

Some people might think you can only use or set environment variable of the service in docker compose eg.:

``` my-service: image: lts-alpine environment: MY_SECRET_KEY: ${MY_SECRET_KEY}

```

But the same ${} syntax can be used to set a version of Docker image of PostgreSQL, like in this example below:

``` my-service: image: postgres:${POSTGRES_VERSION:-13}-alpine

```

If nothing is set, version 13 is the fallback value. Now you can set POSTGRES_VERSION environment via your shell. Or leverage the .env file of Docker:

``` POSTGRES_VERSION=16

```

When running: docker compose --env-file .env up, Docker should now use PostgreSQL v16 Alpine as Docker image.

Bonus: The docker-compose.yml filename is an old filename, use compose.yml from now. Same for other Compose files like compose.override.yml.

More info: https://docs.docker.com/compose/environment-variables/set-environment-variables/ and https://docs.docker.com/compose/environment-variables/set-environment-variables/

Lemmy was/is vulnerable for XSS attacks.

Hackers try to inject JavaScript code that tries to steal your (ideally admin) cookie credentials. It seems that the admin account of lemmy.world was compromised this way (MichelleG). Other instances aren't safe either. Which could point to the custom emojis feature in the federate comments, meaning a lot of external instances could be effected by now.

Incorrect escaping of user input data could lead to these issues. Kbin just recently discovered a similar regression issue and which has been solved by now. But it seems that Lemmy was or still is vulnerable to this attack factor.

Mitigation action Lemmy users: You might want to disable JavaScript in the meanwhile.

Mitigation action for Lemmy server owner: Disable custom emoji:

``` DELETE FROM custom_emoji_keyword; DELETE FROM custom_emoji;

```

Clean-up the exploit content:

``` UPDATE comment SET content = '<REMOVED BY ADMIN>' WHERE content LIKE '%![" onload%'; UPDATE private_message SET content = '<REMOVED BY ADMIN>' WHERE content LIKE '%![" onload%'; UPDATE post SET body = '<REMOVED BY ADMIN>' WHERE body LIKE '%![" onload%'; UPDATE post SET name = '<REMOVED BY ADMIN>' WHERE name LIKE '%![" onload%';

```

Rotate your JWT secret (invalidates all current login sessions):

``` UPDATE secret SET jwt_secret = gen_random_uuid();

```

Note: Even just opening a link to a vulnerable Lemmy instance could allow hackers to steal your cookies or sessions credentials. Therefore I will not share or allow people to share URLs of comprised / vulnerable instances.