The Matrix specification before 1.16 (i.e., with a room version before 12) lacks create event uniqueness.
https://matrix.org/blog/2025/08/project-hydra-improving-state-res/
https://github.com/matrix-org/matrix-spec/releases/tag/v1.16
Source: Mitre, NVD
Published: 2025-10-02
Updated: 2026-04-15
Base Score: 5.6
Vector: CVSS2#AV:N/AC:H/Au:S/C:N/I:C/A:P
Severity: Medium
Base Score: 7.1
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:N/I:H/A:L
Severity: High
EPSS: 0.00039