CVE-2026-63115 (GCVE-0-2026-63115)
Vulnerability from cvelistv5 – Published: 2026-10-30 21:33 – Updated: 2026-11-02 18:09
VLAI
EPSS
VEX
Title
ActivityPub Undo handler can unfollow or remove reposts on behalf of other accounts
Summary
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.
Severity
5.3 (Medium)
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-11-02 17:12 UTC
CWE
Assigner
GitHub_M
CNA
References
4 references
| URL | Tags |
|---|---|
| https://github.com/TryGhost/ActivityPub/security/… | x_refsource_CONFIRM |
| https://github.com/TryGhost/ActivityPub/pull/1929 | x_refsource_MISC |
| https://github.com/TryGhost/ActivityPub/commit/15… | x_refsource_MISC |
| https://github.com/TryGhost/ActivityPub/releases/… | x_refsource_MISC |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| TryGhost | ActivityPub |
Affected:
>= 1.0.0, < 1.2.6
|
{
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-63115",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "yes"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-11-02T17:12:41.067713Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-11-02T18:09:53.602Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"product": "ActivityPub",
"vendor": "TryGhost",
"versions": [
{
"status": "affected",
"version": "\u003e= 1.0.0, \u003c 1.2.6"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "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\u0027s involvement. No private data is exposed and content is not modified; the affected relationships can be re-established. Services proxying to Ghost\u0027s 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."
}
],
"metrics": [
{
"cvssV3_1": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "NONE",
"baseScore": 5.3,
"baseSeverity": "MEDIUM",
"confidentialityImpact": "NONE",
"integrityImpact": "LOW",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
"version": "3.1"
}
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-290",
"description": "CWE-290: Authentication Bypass by Spoofing",
"lang": "en",
"type": "CWE"
}
]
},
{
"descriptions": [
{
"cweId": "CWE-345",
"description": "CWE-345: Insufficient Verification of Data Authenticity",
"lang": "en",
"type": "CWE"
}
]
},
{
"descriptions": [
{
"cweId": "CWE-863",
"description": "CWE-863: Incorrect Authorization",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-10-30T21:33:55.894Z",
"orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"shortName": "GitHub_M"
},
"references": [
{
"name": "https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc",
"tags": [
"x_refsource_CONFIRM"
],
"url": "https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc"
},
{
"name": "https://github.com/TryGhost/ActivityPub/pull/1929",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/TryGhost/ActivityPub/pull/1929"
},
{
"name": "https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e"
},
{
"name": "https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6"
}
],
"source": {
"advisory": "GHSA-mm4q-93gr-5mwc",
"discovery": "UNKNOWN"
},
"title": "ActivityPub Undo handler can unfollow or remove reposts on behalf of other accounts"
}
},
"cveMetadata": {
"assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"assignerShortName": "GitHub_M",
"cveId": "CVE-2026-63115",
"datePublished": "2026-10-30T21:33:55.894Z",
"dateReserved": "2026-07-15T16:54:55.816Z",
"dateUpdated": "2026-11-02T18:09:53.602Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"vulnrichment": {
"containers": {
"adp": [
{
"metrics": [
{
"other": {
"content": {
"id": "CVE-2026-63115",
"options": [
{
"Exploitation": "none"
},
{
"Automatable": "yes"
},
{
"Technical Impact": "partial"
}
],
"role": "CISA Coordinator",
"timestamp": "2026-11-02T17:12:41.067713Z",
"version": "2.0.3"
},
"type": "ssvc"
}
}
],
"providerMetadata": {
"dateUpdated": "2026-11-02T17:12:41.914Z",
"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"shortName": "CISA-ADP"
},
"title": "CISA ADP Vulnrichment"
}
],
"cna": {
"affected": [
{
"product": "ActivityPub",
"vendor": "TryGhost",
"versions": [
{
"status": "affected",
"version": "\u003e= 1.0.0, \u003c 1.2.6"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "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\u0027s involvement. No private data is exposed and content is not modified; the affected relationships can be re-established. Services proxying to Ghost\u0027s 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."
}
],
"metrics": [
{
"cvssV3_1": {
"attackComplexity": "LOW",
"attackVector": "NETWORK",
"availabilityImpact": "NONE",
"baseScore": 5.3,
"baseSeverity": "MEDIUM",
"confidentialityImpact": "NONE",
"integrityImpact": "LOW",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
"version": "3.1"
}
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-290",
"description": "CWE-290: Authentication Bypass by Spoofing",
"lang": "en",
"type": "CWE"
}
]
},
{
"descriptions": [
{
"cweId": "CWE-345",
"description": "CWE-345: Insufficient Verification of Data Authenticity",
"lang": "en",
"type": "CWE"
}
]
},
{
"descriptions": [
{
"cweId": "CWE-863",
"description": "CWE-863: Incorrect Authorization",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-10-30T21:33:55.894Z",
"orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"shortName": "GitHub_M"
},
"references": [
{
"name": "https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc",
"tags": [
"x_refsource_CONFIRM"
],
"url": "https://github.com/TryGhost/ActivityPub/security/advisories/GHSA-mm4q-93gr-5mwc"
},
{
"name": "https://github.com/TryGhost/ActivityPub/pull/1929",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/TryGhost/ActivityPub/pull/1929"
},
{
"name": "https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/TryGhost/ActivityPub/commit/1526f540b983da97750b380868a210e6cdfb985e"
},
{
"name": "https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/TryGhost/ActivityPub/releases/tag/v1.2.6"
}
],
"source": {
"advisory": "GHSA-mm4q-93gr-5mwc",
"discovery": "UNKNOWN"
},
"title": "ActivityPub Undo handler can unfollow or remove reposts on behalf of other accounts"
}
},
"cveMetadata": {
"assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"assignerShortName": "GitHub_M",
"cveId": "CVE-2026-63115",
"datePublished": "2026-10-30T21:33:55.894Z",
"dateReserved": "2026-07-15T16:54:55.816Z",
"dateUpdated": "2026-11-02T18:09:53.602Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
}
}
Loading…
Loading…
Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.
Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline
Sightings and recorded dates, grouped by day · UTC
Loading timeline…
Loading…
Loading…
The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
Loading…
Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.