CVE-2026-70367
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.
CSIRTS triage
- What
- SOCKS proxy in Stunnel can be bypassed via IPv4-mapped IPv6 loopback and unspecified addresses, allowing unauthorized access to loopback-only services.
- Who is affected
- Stunnel deployments using SOCKS proxy that restrict access to loopback services.
- Urgency
- Medium priority; SSRF bypass allows circumvention of network access controls on loopback services, though not currently exploited.
- Action
- Update Stunnel to a patched version that properly validates IPv4-mapped IPv6 addresses in SOCKS proxy filtering.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.15% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 5% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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