Vulnerability in matrix-synapse (CVE-2021-21393)
Summary
Vulnerability in matrix-synapse (CVE-2021-21393). Risk of unauthorized operations or information disclosure. Exploitable via enable_group_creation. Mitigation: upgrade to 1.28.0 or later.
Original description
The description as published by the source.
Impact
Missing input validation of some parameters on the groups (also known as communities) endpoints could cause excessive use of disk space and memory leading to resource exhaustion. Additionally clients may have issues rendering large fields.
Patches
This issue is fixed by #9321 and #9393.
Workarounds
The groups feature can be disabled (by setting enable_group_creation to False) to mitigate this issue. Note that it is disabled by default.
Other information
Note that the groups feature is not part of the Matrix specification and the chosen maximum lengths are arbitrary. Not all clients might abide by them.
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-2021-21393 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 1.28.0 or later.
If unsure, ask your IT team or search "matrix-synapse CVE-2021-21393" on the vendor's site.
CVE-2021-21393 (matrix-synapse) — CWE-20
Attack vector: remote (network-reachable) / no user interaction
Attack surface: enable_group_creation / False
Patched: 1.28.0 — apply immediately
Workaround: The groups feature can be disabled (by setting enable_group_creation to False) to mitigate this issue.
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.
A vulnerability (CWE-20) exists in matrix-synapse. Attackers reach the vulnerable code path via enable_group_creation.
Check the vendor advisory for the affected versions of matrix-synapse. Attack surface: enable_group_creation / False.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 1.28.0.
Workaround: The groups feature can be disabled (by setting enable_group_creation to False) to mitigate this issue.
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
-
1Identify 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。 -
2Apply temporary workaround mitigate
The groups feature can be disabled (by setting `enable_group_creation` to `False`) to mitigate this issue.パッチが適用されるまでの応急処置として、The groups feature can be disabled (by setting
enable_group_creationtoFalse) to mitigate this issue. を実施。回避策の副作用 (機能低下) を確認した上で。 -
3Apply patch patch
Upgrade matrix-synapse to 1.28.0ステージング環境で 1.28.0 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。
-
4Post-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
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2021-21393 matrix-synapse Fixed in: 1.28.0-1
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web lists.fedoraproject.org
- web pypi.org