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MEDIUM severity

CVE-2026-78135 — strongswan

MEDIUM

CVE-2026-78135 is a medium-severity (CVSS 5.6) CWE-841 vulnerability. A fix is available — see the affected versions and patch details below.

Published
Updated
Affected
1 product
Patched
See advisory
Exploits
None indexed
Exploitation data as of Oct 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-78135.

EPSS Exploitation Probability

via FIRST.org ↗
0.4%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs28th percentile — riskier than 28% of all scored CVEsHighest risk
0.00%0.29%0.57%0.86%0.4%0.4%Oct 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-78135 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Description

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.

Affected Products

1 product · 1 configurations
Application
strongswanstrongswan
≥ 5.9.7 && ≤ 6.0.7
range

Detection & mitigation playbook

Vulnerability

  1. Detect

    Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).

  2. Fix

    Upgrade the affected component to the fixed release for CVE-2026-78135, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.

  3. Workarounds

    Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

UbuntuMEDIUM
USN-8789-1Ubuntu

Frequently Asked Questions

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.
O3 Security · Impact-Aware SCA

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CVE-2026-78135: strongswan Auth Bypass (Medium 5.6)