ActivityPub Undo handler can unfollow or remove reposts on behalf of other accounts
CVSS score
5.3
EPSS probability
—
Risk score
0.5
Published
2 h ago
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Impact on My Inventory
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Vulnerability description
DayBreach AI Explanation
Verified against sourcesSources read
1
Source agreement
Tam uyum
Evidence confidence
%55
Short explanation
In TryGhost ActivityPub versions 1.0.0 through 1.2.6, the Undo handler allows a remote federated server to act as if an activity came from a different account [S0]. This permits the removal of existing follow relationships or reposts belonging to another account without involvement [S0].
This vulnerability allows attackers to remove follow relationships and reposts belonging to other accounts without authorization [S0]. Although private data is not exposed, account trust and integrity are impacted [S0].
What should be done?
- Ensure hosted services are updated as managed by providers [S0].
- Redeploy self-hosted services using an updated image [S0].
- Review vendor advisories for ongoing patch status [S0].
Chain of evidence and sources
TryGhost ActivityPub sürümleri 1.0.0 ile 1.2.6 arasında Undo işleyicisi yetkisiz kaldırma işlemlerine izin verir.
Etkilenen ilişkiler yeniden kurulabilmekte olup özel veriler ifşa edilmemektedir.
Show the technical text from the sources
ActivityPub is a multi-tenant ActivityPub server for Ghost, built with Fedify. From 1.0.0 until 1.2.6, the `Undo` handler allows a remote federated server to cause the service to act on a `follow` or `repost` as though the activity came from a different account. This permits removal of an existing `follow` relationship or `repost` belonging to another account without that account's involvement. No private data is exposed and content is not modified; the affected relationships can be re-established. Services proxying to Ghost's hosted ActivityPub server have already been updated, while self-hosted services require an updated image and redeployment. This issue is fixed in version 1.2.6.
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
CWE: CWE-290, CWE-345, CWE-863
This explanation was compiled automatically from the source records. Scores, active exploitation, patch and exploit status come straight from the sources.
IMPACT: Affected Products and Software
Affected Products
The following products are affected by CVE-2026-63115 vulnerability. Where our threat engine knows the exact affected versions, they are listed below.
| ID | VENDOR | PRODUCT | ACTION |
|---|---|---|---|
| 1 | TryGhost | ActivityPub | View |
RED HAT CSAF/VEX: Product Impact Check
SCORING: CVSS from Multiple Sources
CVSS Scores
The Common Vulnerability Scoring System is a standardised framework for assessing the severity of vulnerabilities in software and systems. We collect and display CVSS scores from several sources for each CVE.
| SCORE | VERSION | SEVERITY | VECTOR | SOURCE |
|---|---|---|---|---|
| 5.3 | CVSS V31 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N | NVD |
| 5.3 | CVSS V3_1 | MEDIUM | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N | CVE CNA |
Patch and Remediation Guide
Solution & Remediation Advisory
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Public exploit and active exploitation status
Verified exploit intelligence
No verified public PoC, exploit repository or Metasploit module has been found for this CVE yet.
Weakness Classification and Attack Patterns (CWE & CAPEC)
CWE - Common Weakness Enumeration
While CVE identifies specific instances of vulnerabilities, CWE categorises the common flaws or weaknesses that can lead to vulnerabilities. CVE-2026-63115 is associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2026-63115 weaknesses.
Attack Vector and Accessibility
Official Sources and Advisories
Similar Vulnerabilities
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