What is CVE-2026-78135?

CVE-2026-78135 is a medium-severity vulnerability in Strongswan, classified under Improper Enforcement of Behavioral Workflow. CVSS score: 5.6/10. Published 2026-09-11.

How severe is CVE-2026-78135?

Medium severity. CVSS v3 base score is 5.6 out of 10.

Vulnerability in Strongswan

CVE-2026-78135

libcharon in strongSwan 5.9.7 through 6.0.7 mishandles behavioral workflow in the IKEv2 state machine. Because CREATE_CHILD_SA requests are mishandled, there can be an authentication bypass.

Published 2026-09-11 · last modified 2026-09-16.

CVSS v3 metric

CVSS v3 base score 5.6 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L.

EPSS exploit prediction

EPSS: 0.004 (36.4th percentile), scored 2026-10-26.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 36.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.001

Affected products

Strongswan

Weakness classification (CWE)

CWE-841 — Improper Enforcement of Behavioral Workflow

References

github.com/strongswan/strongswan/releases/tag/6.1.0 (Release Notes, Vendor Advisory)
www.strongswan.org/blog/2026/09/07/strongswan-vulnerability-(cve-2026-78135).ht… (Mitigation, Vendor Advisory)

Frequently asked questions

What is CVE-2026-78135?: CVE-2026-78135 is a medium-severity vulnerability in Strongswan, classified under Improper Enforcement of Behavioral Workflow. CVSS score: 5.6/10. Published 2026-09-11.
How severe is CVE-2026-78135?: Medium severity. CVSS v3 base score is 5.6 out of 10.