CVE-2026-53950 — @tryghost/activitypub
HIGHCVE-2026-53950 is a high-severity (CVSS 7.5) Cross-site Scripting (XSS) vulnerability in @tryghost/activitypub. A fix is available for @tryghost/activitypub — see the affected versions and patch details below.
@tryghost/activitypub: XSS in Ghost's ActivityPub client
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-53950.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-53950 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
@tryghost/activitypubnpmDescription
Impact
The ActivityPub client in Ghost was vulnerable to JavaScript injection on posts shared by a maliciously customised ActivityPub server.
Vulnerable Versions
This vulnerability is present in the @tryghost/activitypub package up to v3.0.8. All prior versions are also affected.
Patches
@tryghost/activitypub v3.1.0 contains a fix for this issue and is also automatically fetched by Ghost.
References
Ghost thanks Brad Geesaman, Ghost Security for disclosing this vulnerability responsibly.
For more information
If you have any questions or comments about this advisory, email Ghost at [email protected].
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @tryghost/activitypub | all versions | 3.1.0npm install @tryghost/activitypub@3.1.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @tryghost/activitypub, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @tryghost/activitypub to 3.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53950 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2026-53950 in your dependencies?
Find it across npm, including transitive dependencies.