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

Is it exploited?

Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of 29 Oct 2026. If CISA adds it, this page shows it as known exploited.

How likely is exploitation in the next 30 days?

0.2%

EPSS score, percentile 4.7 of all scored records. A probability estimated by FIRST, not a report of exploitation.

CISA's SSVC assessment in the CVE record lists exploitation as poc.

How severe?

5.4 Medium

CVSS v3.1 base score, given by the CNA

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

The CVE record links no vendor advisory, patch or mitigation.

Which versions are affected?

Affected

• from 5.25 to before 5.80

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026; CVE List, as of 29 Oct 2026. About the data.

What to do

Workaround (from the CVE record)

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.

Advisories and patches

The CVE record links no vendor advisory, patch or mitigation.

This summary is based on the CVE record as of 29 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

As listed in the CVE record.

Versions not listed are: unaffected.

Versions not listed are: affected.

Versions not listed are: unaffected.

Versions not listed are: unaffected.

Versions not listed are: affected.

Versions not listed are: affected.

Source: CVE List, as of 29 Oct 2026. About the data.

About this vulnerability

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-rea…

Summary: CVE record, as of 29 Oct 2026.

• CISA has not added CVE-2026-70367 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
• The CVE record was published on 4 Aug 2026.
• The CVE record carries a CVSS v3.1 base score of 5.4 (Medium), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 0.2% (percentile 4.7), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
• CISA's SSVC assessment in the CVE record: exploitation poc, automatable no, technical impact partial.
• The credits in the CVE record name AISLE as finder.

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; CVE List, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026. About the data.

Description

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

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.

Source: CVE List, as of 29 Oct 2026. About the data.

Timeline