Vulnerability in matrix-synapse (CVE-2021-29471)
Summary
Vulnerability in matrix-synapse (CVE-2021-29471). Risk of unauthorized operations or information disclosure. Exploitable via event_match. Mitigation: upgrade to 1.33.2 or later.
Original description
The description as published by the source.
Impact
"Push rules" can specify conditions under which they will match, including event_match, which matches event content against a pattern including wildcards.
Certain patterns can cause very poor performance in the matching engine, leading to a denial-of-service when processing moderate length events.
Patches
The issue is patched by https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c.
Workarounds
A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy.
For more information
If you have any questions or comments about this advisory, email 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-2021-29471 has been found in matrix-synapse.
Attackers can target a specific entry point like event_match over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade matrix-synapse to 1.33.2 or later.
If unsure, ask your IT team or search "matrix-synapse CVE-2021-29471" on the vendor's site.
CVE-2021-29471 (matrix-synapse) — CWE-331
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: event_match
Patched: 1.33.2 — apply immediately
Workaround: A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy.
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-331) exists in matrix-synapse. Attackers reach the vulnerable code path via event_match without authentication.
Check the vendor advisory for the affected versions of matrix-synapse. Attack surface: event_match.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 1.33.2.
Workaround: A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy.
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
A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy.パッチが適用されるまでの応急処置として、A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy. 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 1.33.2ステージング環境で 1.33.2 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-2021-29471 matrix-synapse Fixed in: 1.33.2-1
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com
- web lists.fedoraproject.org