The on_get_missing_events function in handlers/federation.py in Matrix Synapse before…
Priority LOW 36Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- High · None · None
- Fix status
- Fixed
Attack profile from CVSS 3.0 · NVD. Fix status from CNA and GitHub.
Summary
The on_get_missing_events function in handlers/federation.py in Matrix Synapse before 0.31.1 has a security bug in the get_missing_events federation API where event visibility rules were not applied correctly.
Why it matters now
EPSS 0.01792 78th percentileScored 2026-11-07
Fix Fixed matrix-synapse (PyPI): 0.31.1
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | — | all versions | — | No fix listed | CNA |
| — | matrix-synapse (PyPI) | before 0.31.1 | 0.31.1 | Patch available | GHSA-v8wm-g9f2-xjv4 |
- — Vendor— Affected all versions Fixed in — No fix listed CNA
- matrix-synapse (PyPI) Vendor— Affected before 0.31.1 Fixed in 0.31.1 Patch available GHSA-v8wm-g9f2-xjv4
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:* | before 0.31.1 | Vulnerable | matrix-org |
- cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:* Versions before 0.31.1 Vulnerable ·matrix-org
Remediation
- Fix · GHSA-v8wm-g9f2-xjv4 matrix-synapse (PyPI) Fixed in 0.31.1 Advisory →
Vendor assessments
Timeline
- 2026-10-02 Threatist record created from CVE-2018-12291
- 2026-10-03 Alias added: GHSA-v8wm-g9f2-xjv4
References
More matrix-org Synapse vulnerabilities
- TI-2023-15617 Synapse Outgoing federation to specific hosts can be disabled by sending malicious invites CVSS 3.1MEDIUM 5.0
- TI-2024-35327 Synapse allows a a malformed invite to break the invitee's `/sync` CVSS 4.0HIGH 8.7
- TI-2019-13571 Matrix Synapse before 1.5.0 mishandles signature checking on some federation APIs. CVSS 3.1CRITICAL 9.8
- TI-2024-36056 Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders CVSS 4.0HIGH 8.2
- TI-2024-35318 Synapse allows unsupported content types to lead to memory exhaustion CVSS 4.0HIGH 8.2
- TI-2018-11846 Matrix Synapse before 0.33.3.1 allows remote attackers to spoof events and possibly have… CVSS 3.0HIGH 8.8
Sources
- CVE-2018-12291 · CVE Program
- CVE-2018-12291 · NVD
- FIRST EPSS
- GHSA-v8wm-g9f2-xjv4 · GitHub Advisory Database · CC BY 4.0
- CVE-2018-12291 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences