Hollo security updates: 0.8.17 and 0.9.25

If you run Hollo, update to 0.8.17 or 0.9.25 now. These releases fix GHSA-r48c-xx2h-fv4g, a DNS rebinding vulnerability in Fedify that could bypass Hollo's server-side request forgery (SSRF) protection and cause requests to reach internal services.

Fedify checked that a hostname resolved only to public addresses, then let the HTTP client resolve it again when connecting. An attacker controlling the hostname's DNS answers could return a public address for validation and a private or loopback address for the connection. Redirects and alternate-document links had the same gap.

The affected Fedify paths used by Hollo include remote document loading (authenticated or not), outbound activity delivery, and WebFinger lookups. On Node.js, which Hollo uses, the fix restricts connections to addresses that passed validation. Hollo's ALLOW_PRIVATE_ADDRESS=true option still permits private destinations; leave it unset for public federation. For full technical details, see the Fedify security announcement and the advisory linked above.

All releases on the supported Hollo 0.8.x and 0.9.x lines up to and including 0.8.16 and 0.9.24 are affected. 0.8.17 and 0.9.25 are the first fixed releases and the latest on those lines, incorporating Fedify 2.1.31 and 2.2.20 respectively. Hollo 0.7.x and earlier are no longer supported under the Hollo security policy; operators on those lines should move to a supported release.

For 0.8.x deployments, update to 0.8.17:

docker pull ghcr.io/fedify-dev/hollo:0.8.17

For 0.9.x deployments, update to 0.9.25:

docker pull ghcr.io/fedify-dev/hollo:0.9.25

After pulling the image, recreate your Hollo container using the new image. With Docker Compose, update the image tag in your Compose file and run docker compose up -d. For source deployments, check out the corresponding release tag, run pnpm install --frozen-lockfile using the pnpm version pinned in that tag's package.json, run pnpm run build, and restart the server.

If you have a large 0.9.x database and are upgrading from a release before 0.9.20, follow the 0.9.20 index preparation instructions before starting the new version to avoid blocking writes during the new version's automatic migration.

Thanks to @finalchild for reporting the DNS rebinding issue to the Fedify project.

If anything is unclear, ask below.