Vulnerability in matrix-synapse (CVE-2021-21333)
Summary
Vulnerability in matrix-synapse (CVE-2021-21333). Data can be tampered with by attackers. Mitigation: upgrade to 1.27.0 or later.
Original description
The description as published by the source.
Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the notification emails sent for notifications for missed messages or for an expiring account are subject to HTML injection. In the case of the notification for missed messages, this could allow an attacker to insert forged content into the email. The account expiry feature is not enabled by default and the HTML injection is not controllable by an attacker. This is fixed in version 1.27.0.
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-2021-21333 has been found in matrix-synapse.
Data can be tampered with by attackers.
What to do: upgrade matrix-synapse to 1.27.0 or later.
If unsure, ask your IT team or search "matrix-synapse CVE-2021-21333" on the vendor's site.
CVE-2021-21333 (matrix-synapse) — CWE-74
Attack vector: remote (network-reachable) / unauthenticated
Patched: 1.27.0 — 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.
A vulnerability (CWE-74) exists in matrix-synapse.
Check the vendor advisory for the affected versions of matrix-synapse.
Severity: ?. Data can be tampered with by attackers.
Update to 1.27.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
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 patch patch
Upgrade matrix-synapse to 1.27.0ステージング環境で 1.27.0 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。
-
3Post-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-2021-21333 matrix-synapse Fixed in: 1.27.0-1
References
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- patch github.com
- patch github.com
- patch github.com
- web github.com
- web lists.fedoraproject.org
- web lists.fedoraproject.org