CVE-2018-5389: The Internet Key Exchange v1 main mode is vulnerable to offline dictionary or brute force attacks

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MEDIUM 5.9REMOTEDOWNGRADE

CVE-2018-5389 is a medium-severity flaw (CVSS 5.9) affecting internet key exchange. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The Internet Key Exchange v1 main mode is vulnerable to offline dictionary or brute force attacks. Reusing a key pair across different versions and modes of IKE could lead to cross-protocol authentication bypasses. It is well known, that the aggressive mode of IKEv1 PSK is vulnerable to offline dictionary or brute force attacks. For the main mode, however, only an online attack against PSK authentication was thought to be feasible. This vulnerabi

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	3.1% (top 12%)
CISA exploited list	No
Weakness	CWE-521
Published	2018-09-06
Last modified	2026-06-17

Publisher (CNA): CERT/CC · Vendor: ietf

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2018-09-06 21:29 UTCPublished CVE record published
2026-06-17 02:00 UTCUpdated Record last modified

ietf internet key exchange DOWNGRADE

Affected: 1.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0

1. Check installed version

apt-cache policy internet-key-exchange || rpm -q internet-key-exchange || internet-key-exchange --version

2. No fixed release: DOWNGRADE to a release before 1.0 (Debian / Ubuntu)

apt-cache madison internet-key-exchange sudo apt install internet-key-exchange=<VERSION_BEFORE_1.0> sudo apt-mark hold internet-key-exchange

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list internet-key-exchange sudo dnf downgrade internet-key-exchange-<VERSION_BEFORE_1.0> sudo dnf versionlock add internet-key-exchange

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-2018-5389?

internet key exchange: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2018-5389 being exploited?

CVE-2018-5389 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-2018-5389 affect?

CVE-2018-5389 affects internet key exchange. Severity is medium (CVSS 5.9). The Internet Key Exchange v1 main mode is vulnerable to offline dictionary or brute force attacks. Reusing a key pair across different versions and modes of IKE could lead to cross-protocol authentication bypasses. It is well known, that th

How urgent is CVE-2018-5389?

Priority 53/100. Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2006-2298 MEDIUM 5.0 DOWNGRADE The Internet Key Exchange version 1 (IKEv1) implementation in the libike library in Solaris 9 and 10 allows re
CVE-2006-1646 MEDIUM 5.0 DOWNGRADE The Internet Key Exchange version 1 (IKEv1) implementation (isakmp_agg.c) in the Shoichi Sakane KAME Project r
CVE-2005-3668 MEDIUM 5.0 DOWNGRADE Multiple buffer overflows in multiple unspecified implementations of Internet Key Exchange version 1 (IKEv1) h
CVE-2005-3667 MEDIUM 5.0 DOWNGRADE Multiple unspecified vulnerabilities in multiple unspecified implementations of Internet Key Exchange version
CVE-2005-3666 HIGH 10.0 DOWNGRADE Multiple unspecified format string vulnerabilities in multiple unspecified implementations of Internet Key Exc

References

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