If you use an affected Fedify release, update now. Two vulnerabilities have been fixed in @fedify/fedify: GHSA-4qhx-hhwf-8685, an inbox origin validation flaw that could let an attacker supply forged objects or suppress genuine activities, and GHSA-8863-8468-7hq7, a flaw in the key ownership check that could authenticate activities as the wrong actor under specific actor-document configurations.

The releases containing both fixes are 2.0.34, 2.1.30, 2.2.19, 2.3.14, and 2.4.4. We recommend 2.4.4, or 2.3.14 if you are staying on the 2.3 line. Under the security policy, Fedify supports the latest two minor lines, currently 2.4 and 2.3. Backported fixes are also available in the releases listed above for 2.0, 2.1, and 2.2, but users on those older lines should plan to move to a supported line. Users on affected 1.x releases need to change their dependency to a supported 2.x release.

Inbox activity origin mismatch (GHSA-4qhx-hhwf-8685, medium, CVSS 6.5)

GHSA-4qhx-hhwf-8685 affects applications receiving activities through Fedify's inbox listeners. The inbox authenticated an activity's actor but accepted an activity id on an origin different from the actor's. An attacker needed only an actor and its signing key on a server they controlled, with no account on the receiving server or interaction from the victim.

Since version 1.9.0, Fedify's property accessors have trusted embedded objects whose IDs share the activity's origin. By choosing an activity ID on a victim server's origin, an attacker could make Create.getObject() and other accessors return forged objects claiming to live on that server without fetching them from it. Depending on the application's attribution and authorization checks, this could cause it to store or display forged content under another server's object ID.

The same missing check also let an attacker reserve a genuine activity's idempotency cache entry by submitting a forged activity with its ID first. The genuine delivery then received 202 Accepted but did not reach the listeners for one day. When a message queue was configured, the suppression applied across all inboxes on the receiving server. This behavior was confirmed in 1.8.15 and subsequent releases before the fixes; releases before 1.8 were not tested.

The first fixes shipped in 2.0.33, 2.1.29, 2.2.18, 2.3.13, and 2.4.3. Earlier releases on each of those 2.x lines are affected. Update to the newer releases recommended above to receive both fixes. The inbox now returns 401 Unauthorized for non-portable activities whose IDs have a different origin from their actors, before they reach listeners, the queue, or the idempotency cache. The same origin check applies to queued and manually routed activities. Setting skipSignatureVerification bypasses this protection along with signature verification.

Actor document identity mismatch (GHSA-8863-8468-7hq7, medium, CVSS 5.9)

GHSA-8863-8468-7hq7 lists the affected version range as <= 2.4.3, with fixes in 2.0.34, 2.1.30, 2.2.19, 2.3.14, and 2.4.4 on their respective release lines. When confirming that a key belongs to an actor, Fedify fetched the actor's document and checked that it listed the key, but did not require the document's id to match the actor ID it requested.

An attacker could have activities authenticated as a victim if dereferencing the victim's exact actor ID led to an actor document whose key the attacker controlled. This could happen through a redirect or alternate-document link to the attacker's document, including on another origin, or when the victim's server directly served a different same-origin actor's document. The attacker cannot normally arrange this: it depends on the server hosting the victim's actor ID. A redirect from some other URL on that server is not enough. No account on the receiving Fedify server is required.

HTTP Signatures, Linked Data Signatures, and Object Integrity Proofs use the affected ownership checks. The fix requires the fetched actor document's id to exactly match the requested actor ID, in addition to the existing origin check. An actor whose ID redirects to a document with a different id can no longer have its keys confirmed through that redirect, even on the same origin and for the same account. Servers that normalize actor URLs should use the canonical actor ID as their keys' owner or controller and their activities' actor.

The built-in KvStore-backed key cache automatically ignores entries created under the weaker check and fetches and verifies those keys again. If you supply a custom KeyCache implementation, clear it once when upgrading. Otherwise, previously cached false ownership claims can remain trusted after the upgrade. Downgrading to an earlier release is not safe.

Updating

Update @fedify/fedify using the command for your package manager:

npm  update  @fedify/fedify
yarn upgrade @fedify/fedify
pnpm update  @fedify/fedify
bun  update  @fedify/fedify
deno update  @fedify/fedify

Check the installed or locked version: it should be 2.0.34, 2.1.30, 2.2.19, 2.3.14, or 2.4.4 on the corresponding line. Update commands can stay within your declared dependency range. If that range excludes the recommended release, change it explicitly. For example, to move to 2.4.4:

npm  install @fedify/fedify@2.4.4
yarn add     @fedify/fedify@2.4.4
pnpm add     @fedify/fedify@2.4.4
bun  add     @fedify/fedify@2.4.4
deno add     jsr:@fedify/fedify@2.4.4

Clear any custom key cache as described above, then redeploy. If you run other Fedify-based servers, update those too.

The full GitHub Security Advisories are GHSA-4qhx-hhwf-8685 and GHSA-8863-8468-7hq7.

Thanks to @2chanhaeng for reporting the inbox activity origin mismatch. The actor document identity mismatch was found by the Fedify maintainers with AI assistance.

If anything is unclear, ask below.