CVE-2026-78135: libcharon in strongSwan 5.9.7 through 6.0.7 mishandles behavioral workflow in the IKEv2 state machine

Routine

MEDIUM 5.6REMOTEUPGRADE

CVE-2026-78135 is a medium-severity flaw (CVSS 5.6) affecting strongswan. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.6 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 64%)
CISA exploited list	No
Weakness	CWE-841
Published	2026-09-11
Last modified	2026-09-16

Publisher (CNA): MITRE · Vendor: strongswan

Last updated 2026-09-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-11 03:16 UTCPublished CVE record published
2026-09-16 19:37 UTCUpdated Record last modified

strongswan strongswan UPGRADE

Affected: >= 5.9.7 and <= 6.0.7

Fixed in: newer than 6.0.7

Safe to downgrade to: a release before 5.9.7

1. Check installed version

apt-cache policy strongswan || rpm -q strongswan || strongswan --version

2. UPGRADE to newer than 6.0.7 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade strongswan

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade strongswan

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 5.9.7 (Debian / Ubuntu)

apt-cache madison strongswan sudo apt install strongswan=<VERSION_BEFORE_5.9.7> sudo apt-mark hold strongswan

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list strongswan sudo dnf downgrade strongswan-<VERSION_BEFORE_5.9.7> sudo dnf versionlock add strongswan

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-78135?

strongswan: upgrade to newer than 6.0.7. Exact commands for each OS are on this page.

Is CVE-2026-78135 being exploited?

CVE-2026-78135 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-78135 affect?

CVE-2026-78135 affects strongswan. Severity is medium (CVSS 5.6). 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.

How urgent is CVE-2026-78135?

Priority 34/100. Remotely exploitable, no login, no user action

Software pages

strongSwan vulnerabilities

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References

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