CVE-2018-12423
Matrix Synapse Authorization Error
CVE-2018-12423 is a high vulnerability (CVSS 7.5) in Matrix Synapse, published June 14, 2018. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.81%, the 78th percentile. Fixed in matrix-synapse 0.31.2.
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- High
- Availability
- None
Exploit likelihood
What each source reports
NVD Score used
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
- Record
CVE-2018-12423- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N - CVSS 2.0
- 5.0 Medium
AV:N/AC:L/Au:N/C:N/I:P/A:N - Updated
- 2026-11-02
CVE List No score
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
- Record
CVE-2018-12423- Updated
- 2026-11-02
EUVDEUVD-2022-3580 No score
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
- Record
EUVD-2022-3580- Updated
- 2026-11-03
GitHub AdvisoriesGHSA-ch5v-fhg8-7gv9
Matrix Synapse Authorization Error
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
- Record
GHSA-ch5v-fhg8-7gv9- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N - Updated
- 2026-11-02
OSV
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
- Record
CVE-2018-12423- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N - Updated
- 2026-11-02
OSVDEBIAN-CVE-2018-12423
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
- Record
DEBIAN-CVE-2018-12423- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N - Updated
- 2026-11-02
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OSVGHSA-ch5v-fhg8-7gv9
Matrix Synapse Authorization Error
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
- Record
GHSA-ch5v-fhg8-7gv9- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N - Updated
- 2026-11-02
OSVPYSEC-2026-844
Matrix Synapse Authorization Error
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
- Record
PYSEC-2026-844- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N - Updated
- 2026-11-02
OSVUBUNTU-CVE-2018-12423
In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.
- Record
UBUNTU-CVE-2018-12423- CVSS 3.0
- 7.5 High
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N - Updated
- 2026-11-02
OSVUSN-6076-1 No score
matrix-synapse vulnerabilities
It was discovered that Synapse incorrectly handled certain inputs. If a user or an automated system were tricked into opening a specially crafted input file, a remote attacker could possibly use this issue to cause a denial of service. (CVE-2019-18835, CVE-2018-12291, CVE-2018-10657)
It was discovered that Synapse incorrectly handled certain inputs. If a user or an automated system were tricked into opening a specially crafted input file, a remote attacker could possibly use this issue to hijack the session. (CVE-2019-11842, CVE-2018-12423)
It was discovered that Synapse incorrectly handled certain inputs. If a user or an automated system were tricked into opening a specially crafted input file, a remote attacker could possibly use this issue to perform spoofing or user impersonation. (CVE-2019-5885, CVE-2018-16515)
- Record
USN-6076-1- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
matrix-synapsePyPI |
before 0.31.2 | 0.31.2 |
matrix-synapseUbuntu:Pro:18.04:LTS |
before 0.24.0+dfsg-1ubuntu0.1~esm1, plus listed versions 0.19.2+dfsg-60.24.0+dfsg-1 |
0.24.0+dfsg-1ubuntu0.1~esm1 |
History
| When | Changed | Sources |
|---|---|---|
| 2026-11-03 | affected | |
| 2026-11-03 | aliases | EUVD |
| 2026-11-02 | created | CVE List, GitHub Advisories, NVD, OSV |
References
matrix.org/blog/2018/06/14/security-update-synapse-0-31-2
github.com/matrix-org/matrix-doc/issues/1304
bugs.debian.org/901549
nvd.nist.gov/vuln/detail/CVE-2018-12423
security-tracker.debian.org/tracker/CVE-2018-12423
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pypi.org/project/matrix-synapse
ubuntu.com/security/CVE-2018-12423
cve.org/CVERecord?id=CVE-2018-12423