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XSS in Ghost's ActivityPub client

High severity GitHub Reviewed Published Jun 10, 2026 in TryGhost/Ghost

Package

npm @tryghost/activitypub (npm)

Affected versions

< 3.1.0

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

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 security@ghost.org.

References

@lsinger lsinger published to TryGhost/Ghost Jun 10, 2026
Published by the National Vulnerability Database Jun 24, 2026
Published to the GitHub Advisory Database Aug 4, 2026
Reviewed Aug 4, 2026

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

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(28th percentile)

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

CVE ID

CVE-2026-53950

GHSA ID

GHSA-xpp7-93x6-v29m

Source code

Credits

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