# CVE-2026-70367: Stunnel: ssrf bypass in stunnel socks proxy via ipv4-mapped ipv6 loopback and unspecified addresses allows access to loopback-only services

Status: published. Published: 2026-08-04. Updated: 2026-11-05.

A Server-Side Request Forgery (SSRF) bypass vulnerability exists in “stunnel” 5.79 and lower when configured in SOCKS proxy mode. This flaw allows a client to bypass intended localhost restrictions by using IPv4-mapped IPv6 addresses (e.g., “::ffff:127.0.0.1”) or unspecified addresses ("0.0.0.0", "::"), enabling access to loopback-only services on the "stunnel" host that should not be network-reachable.

## Remediation

- workaround: To mitigate this issue, if SOCKS proxying functionality is not required, disable the "protocol = socks" configuration in "stunnel". If SOCKS proxying is necessary, restrict access to the SOCKS listener by binding it to a trusted management network or localhost, and enforce client authentication or network ACL controls. Run "stunnel" in a container or network namespace where no other services are bound to localhost, or add firewall rules to restrict outgoing connections from "stunnel" to localhost. (source: CNA: redhat)

## Affected products and versions

- Mobi-Com Polska Sp. z o.o. / stunnel: ≥ 5.25; < 5.80 (affected, custom). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 10 (stunnel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (stunnel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 (stunnel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (stunnel): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (stunnel): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 5.4 (medium); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 0.16% as of 2026-11-05; percentile 4.73%

- SSVC: exploitation poc; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-918

## Exploit evidence

- exploit: https://bugzilla.redhat.com/show_bug.cgi?id=2462083 (ADP: CISA-ADP)

## References

- https://access.redhat.com/security/cve/CVE-2026-70367 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2462083 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2462083 (ADP: CISA-ADP; exploit)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-70367; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-70367; retrieved 2026-11-05; source updated Not reported

Revision: 236ece1f62edb13be0fcd1e2852cef5bf6155aff3e37e92088d192207fa56efc

Canonical: https://y2.dev/cve/CVE-2026-70367

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