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.
Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.


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.

History

Tue, 04 Aug 2026 15:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Tue, 04 Aug 2026 14:15:00 +0000

Type Values Removed Values Added
First Time appeared Stunnel
Stunnel stunnel
Vendors & Products Stunnel
Stunnel stunnel

Tue, 04 Aug 2026 14:00:00 +0000

Type Values Removed Values Added
Title stunnel: SSRF bypass in stunnel SOCKS proxy via IPv4-mapped IPv6 loopback and unspecified addresses allows access to loopback-only services Stunnel: ssrf bypass in stunnel socks proxy via ipv4-mapped ipv6 loopback and unspecified addresses allows access to loopback-only services
First Time appeared Redhat
Redhat enterprise Linux
CPEs cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:6
cpe:/o:redhat:enterprise_linux:7
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
Vendors & Products Redhat
Redhat enterprise Linux
References

Tue, 04 Aug 2026 12:15:00 +0000

Type Values Removed Values Added
Description 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.
Title stunnel: SSRF bypass in stunnel SOCKS proxy via IPv4-mapped IPv6 loopback and unspecified addresses allows access to loopback-only services
Weaknesses CWE-918
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.4, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N'}

threat_severity

Moderate


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: redhat

Published:

Updated: 2026-08-06T07:28:08.760Z

Reserved: 2026-08-04T07:03:23.572Z

Link: CVE-2026-70367

cve-icon Vulnrichment

Updated: 2026-08-04T14:49:53.911Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-08-04T14:16:32.557

Modified: 2026-08-06T15:37:22.093

Link: CVE-2026-70367

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-08-04T10:29:57Z

Links: CVE-2026-70367 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-08-04T19:15:03Z

Weaknesses