CVE-2026-55103 Discourse ActivityPub - Broken Access Control

Discourse ActivityPub prior to commit 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5 contains a broken access control vulnerability caused by insufficient verification of actor identity and ownership in inbound ActivityPub processing, letting remote attackers edit, delete, or reply to federated posts without permissions, exploit requires crafted signed requests.

CVSS base score 8.6 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Not required
View the NVD record ↗

Details

Type
Broken Access Control
Impact
Data Tampering
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
Published
15 October 2026
Updated
16 October 2026
Weakness
CWE-345

Vendor fix

Update to the version including commit 1c8518b0f2abdf31cbea3e0b242f74d8994a9ba5 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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