Vulnerability in stunnel4
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 DEBIAN-CVE-2021-20230 has been found in stunnel4.
Confidential information can be exposed externally.
What to do: upgrade stunnel4 to 3:5.56+dfsg-8 or later.
If unsure, ask your IT team or search "stunnel4 DEBIAN-CVE-2021-20230" on the vendor's site.
DEBIAN-CVE-2021-20230 (stunnel4)
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 3:5.56+dfsg-8 — 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 (unclassified) exists in stunnel4.
Check the vendor advisory for the affected versions of stunnel4.
Severity: ?. Confidential information can be exposed externally.
Update to 3:5.56+dfsg-8.
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 'stunnel4' . 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
Identify exposureidentify
grep -r 'stunnel4' . | 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
stunnel4を grep し、稼働しているサービス・バージョンを把握する。 -
2
Apply patchpatch
Upgrade stunnel4 to 3:5.56+dfsg-8ステージング環境で 3:5.56+dfsg-8 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
Post-deployment verificationverify
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
| Ecosystem | Package | Affected | Fixed |
|---|---|---|---|
| Debian:11 | stunnel4 |
< 3:5.56+dfsg-8 |
3:5.56+dfsg-8 |
| Debian:12 | stunnel4 |
< 3:5.56+dfsg-8 |
3:5.56+dfsg-8 |
| Debian:13 | stunnel4 |
< 3:5.56+dfsg-8 |
3:5.56+dfsg-8 |
Original description The description as published by the source.
A flaw was found in stunnel before 5.57, where it improperly validates client certificates when it is configured to use both redirect and verifyChain options. This flaw allows an attacker with a certificate signed by a Certificate Authority, which is not the one accepted by the stunnel server, to access the tunneled service instead of being redirected to the address specified in the redirect option. The highest threat from this vulnerability is to confidentiality.
Source: OSV.dev (Open Source Vulnerabilities) OSV
References
- advisory security-tracker.debian.org