CVE-2021-39163

LOWNVD 3.13.1—
EchelonGraph scoreMEDIUM confidence

This low-severity CVE scores 3.1 under NVD CVSS v3. EPSS exploit probability: 0.3%, top 49% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
3.1
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 1%CVSS: 3.1Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Matrix is an ecosystem for open federated Instant Messaging and Voice over IP. In versions 1.41.0 and prior, unauthorised users can access the name, avatar, topic and number of members of a room if they know the ID of the room. This vulnerability is limited to homeservers where the vulnerable homeserver is in the room and untrusted users are permitted to create groups (communities). By default, only homeserver administrators can create groups. However, homeserver administrators can already access this information in the database or using the admin API. As a result, only homeservers where the configuration setting enable_group_creation has been set to true are impacted. Server administrators should upgrade to 1.41.1 or higher to patch the vulnerability. There are two potential workarounds. Server administrators can set enable_group_creation to false in their homeserver configuration (this is the default value) to prevent creation of groups by non-administrators. Administrators that are using a reverse proxy could, with partial loss of group functionality, block the endpoints /_matrix/client/r0/groups/{group_id}/rooms and /_matrix/client/unstable/groups/{group_id}/rooms.

CVSS v3
3.1
EG Score
3.1(medium)
EPSS
55.2%
KEV
Not listed

Published

August 31, 2021

Last Modified

November 21, 2024

References (10)

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
matrix-synapse0.33.5 ... 1.9.1 (197 versions)1.41.1—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 7× in last 7d / 45× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-11 08:25 UTCEPSS rescore
  2. 2026-07-11 08:25 UTCEPSS rescore
  3. 2026-07-09 19:07 UTCEPSS rescore
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  15. 2026-06-30 16:30 UTCOSV refresh
  16. 2026-06-29 14:04 UTCEPSS rescore
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  20. 2026-06-27 03:06 UTCEPSS rescore
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  1. 2026-06-23 21:31 UTCEPSS rescore
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  4. 2026-06-21 14:55 UTCEPSS rescore
  5. 2026-06-21 01:58 UTCEPSS rescore
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  7. 2026-06-19 19:24 UTCEPSS rescore
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  9. 2026-06-18 17:51 UTCEPSS rescore
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  18. 2026-06-12 23:10 UTCEPSS rescore
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  20. 2026-06-12 23:07 UTCOSV refresh
  21. 2026-06-11 13:58 UTCEPSS rescore
  22. 2026-06-10 22:16 UTCEPSS rescore
  23. 2026-06-10 13:20 UTCEPSS rescore
  24. 2026-06-08 14:15 UTCEPSS rescore
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  26. 2026-06-07 15:23 UTCEPSS rescore
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  40. 2026-05-31 22:29 UTCEPSS rescore
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  42. 2026-05-31 00:15 UTCEPSS rescore
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  44. 2026-05-29 13:42 UTCEPSS rescore
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  46. 2026-05-28 13:43 UTCEPSS rescore
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  48. 2026-05-27 13:39 UTCEPSS rescore
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  50. 2026-05-27 13:39 UTCEPSS rescore
  51. 2026-05-26 13:42 UTCEPSS rescore
  52. 2026-05-26 11:14 UTCEG score recompute
  53. 2026-05-26 07:17 UTCEPSS rescore
  54. 2026-05-26 07:17 UTCEPSS rescore
  55. 2026-05-26 07:17 UTCEPSS rescore
  56. 2026-05-25 20:46 UTCOSV refresh

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2021-39163?
CVE-2021-39163 is a low vulnerability published on August 31, 2021. Matrix is an ecosystem for open federated Instant Messaging and Voice over IP. In versions 1.41.0 and prior, unauthorised users can access the name, avatar, topic and number of members of a room if they know the ID of the room. This vulnerability is limited to homeservers where the vulnerable…
When was CVE-2021-39163 disclosed?
CVE-2021-39163 was first published in the National Vulnerability Database on August 31, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-39163 actively exploited?
CVE-2021-39163 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 55.2% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-39163?
CVE-2021-39163 has a CVSS v3 base score of 3.1 (NVD).
How do I remediate CVE-2021-39163?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-39163, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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