Stunnel: ssrf bypass in stunnel socks proxy via ipv4-mapped ipv6 loopback and unspecified addresses allows access to loopback-only services
CVE-2026-70367 is fixed in stunnel on 1 platform, first by DEBIAN-CVE-2026-70367, released August 8, 2026. It is not reported as exploited. Patch Radar priority: Routine.
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.
Where it's fixed
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| stunnel · Debian 14 | 3:5.80-1 | DEBIAN-CVE-2026-70367 | Aug 8, 2026 |
| stunnel · opensuse-leap 16.0 | 5.74-160000.3.1 | OPENSUSE-SU-2026:22088-1 | Nov 7, 2026 |
| stunnel · sles 15.7 | 5.70-150600.3.6.1 | SUSE-SU-2026:4617-1 | Nov 7, 2026 |
| stunnel · sles 16.0 | 5.74-160000.3.1 | SUSE-SU-2026:24232-1 | Nov 7, 2026 |
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