Vulnerability in @fedify/fedify (CVE-2026-42462)
Summary
Vulnerability in @fedify/fedify (CVE-2026-42462). Data can be tampered with by attackers. Exploitable via Activity. Mitigation: upgrade to 1.9.11 or later.
Original description
The description as published by the source.
As told on Discord earlier, multiple projects are affected, and we would like to coordinate. For now, we are aiming at a May 6th release date, but this is not set in stone yet.
Summary
An attacker can make use of JSON-LD features to restructure a JSON-LD document that would change how Fedify interprets it without changing its Linked Data Signature, allowing them to alter a third-party signed activity they have received.
Details
The vulnerability essentially boils down to the signature being on the canonical RDF graph representation of the JSON-LD document, and JSON-LD offering many ways to represent the same graph.
One of the issues is that by taking a signed Activity with an embedded object, an attacker can move the top-level Activity to a @graph property and move the activity's object to the top-level. Such a transformation preserves the signature and changes how the payload is interpreted by pretty much all ActivityPub implementations, making them process the object and ignore the formely-top-level activity. This can be used when the graph contains an embedded activity. In Mastodon, that is the case of { "type": "Undo", "object": { "type": "Announce" } }, but other implementations may sign other activities that can be exploited in the same way.
The @reverse keyword can also be used to change the shape of a JSON-LD document without changing the underlying graph, and could be used in a similar way to reverse an Activity and its object.
Anothe…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-42462 has been found in @fedify/fedify.
Attackers can target a specific entry point like Activity over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 7.0/10.
What to do: upgrade @fedify/fedify to 1.9.11 or later.
If unsure, ask your IT team or search "@fedify/fedify CVE-2026-42462" on the vendor's site.
CVE-2026-42462 (@fedify/fedify) — CWE-180 / CVSS v3 7.0
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Activity / object / Create / Update
Patched: 1.9.11 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-180) exists in @fedify/fedify. Attackers reach the vulnerable code path via Activity without authentication.
Check the vendor advisory for the affected versions of @fedify/fedify. Attack surface: Activity / object / Create / Update.
Severity: High (CVSS 7.0/10). Data can be tampered with by attackers.
Update to 1.9.11.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r '@fedify/fedify' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r '@fedify/fedify' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
@fedify/fedifyを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade @fedify/fedify to 1.9.11ステージング環境で 1.9.11 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory nvd.nist.gov
- package github.com
- web security-advisories@github.com
- web security-advisories@github.com
- web github.com