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XSS in Ghost's ActivityPub client

High
lsinger published GHSA-xpp7-93x6-v29m Jun 10, 2026

Package

npm @tryghost/activitypub (npm)

Affected versions

< 3.0.8

Patched versions

3.1.0

Description

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

We thank Brad Geesaman, Ghost Security for disclosing this vulnerability responsibly.

For more information

If you have any questions or comments about this advisory, email us at security@ghost.org.

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

CVE ID

CVE-2026-53950

Weaknesses

No CWEs

Credits