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CVE-2021-39163

Information Disclosure in matrix-synapse (CVE-2021-39163)

Summary

Vulnerability in matrix-synapse (CVE-2021-39163). Risk of unauthorized operations or information disclosure. Exploitable via enable_group_creation. Mitigation: upgrade to 1.41.1 or later.

Original description

The description as published by the source.

Impact

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.

Patches

Server administrators should upgrade to 1.41.1 or higher.

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 following endpoints:

  • /_matrix/client/r0/groups/{group_id}/rooms
  • /_matrix/client/unstable/groups/{group_id}/rooms

References

n/a

For more information

If you have any questions or comments about this advisory, e-mail us at security@matrix.org.

Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2021-39163 has been found in matrix-synapse.
Attackers can target a specific entry point like enable_group_creation over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade matrix-synapse to 1.41.1 or later.
If unsure, ask your IT team or search "matrix-synapse CVE-2021-39163" on the vendor's site.

CVE-2021-39163 (matrix-synapse) — CWE-200
Attack vector: remote (network-reachable) / no user interaction
Attack surface: enable_group_creation / true / false
Patched: 1.41.1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Information disclosure (CWE-200) exists in matrix-synapse. Attackers reach the vulnerable code path via enable_group_creation.

📍 Affected scope

Check the vendor advisory for the affected versions of matrix-synapse. Attack surface: enable_group_creation / true / false.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 1.41.1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'matrix-synapse' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'matrix-synapse' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で matrix-synapse を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade matrix-synapse to 1.41.1

    ステージング環境で 1.41.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

PyPI matrix-synapse
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.41.1"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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