CVE-2018-15836: In verify_signed_hash() in lib/liboswkeys/signatures.c in Openswan before 2.6.50.1, the RSA implementation doe

Q: How do I fix CVE-2018-15836?

openswan: upgrade to 2.6.50.1. Exact commands for each OS are on this page.

Q: Is CVE-2018-15836 being exploited?

CVE-2018-15836 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2018-15836 affect?

CVE-2018-15836 affects openswan. Severity is high (CVSS 7.5). In verify_signed_hash() in lib/liboswkeys/signatures.c in Openswan before 2.6.50.1, the RSA implementation does not verify the value of padding string during PKCS#1 v1.5 signature verification. Consequently, a remote attacker can forge sign

Q: How urgent is CVE-2018-15836?

Priority 50/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2018-15836 is a high-severity flaw (CVSS 7.5) affecting openswan. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In verify_signed_hash() in lib/liboswkeys/signatures.c in Openswan before 2.6.50.1, the RSA implementation does not verify the value of padding string during PKCS#1 v1.5 signature verification. Consequently, a remote attacker can forge signatures when small public exponents are being used. IKEv2 signature verification is affected when RAW RSA keys are used.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.5% (top 25%)
CISA exploited list	No
Weakness	CWE-347
Published	2018-09-26
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: xelerance

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

Am I affected?

Timeline

2018-09-26 21:29 UTCPublished CVE record published
2026-06-17 01:43 UTCUpdated Record last modified

xelerance openswan UPGRADE

Affected: < 2.6.50.1

Fixed in: 2.6.50.1

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 2.6.50.1 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade openswan

Note

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

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-2018-15836?

openswan: upgrade to 2.6.50.1. Exact commands for each OS are on this page.

Is CVE-2018-15836 being exploited?

CVE-2018-15836 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-2018-15836 affect?

CVE-2018-15836 affects openswan. Severity is high (CVSS 7.5). In verify_signed_hash() in lib/liboswkeys/signatures.c in Openswan before 2.6.50.1, the RSA implementation does not verify the value of padding string during PKCS#1 v1.5 signature verification. Consequently, a remote attacker can forge sign

How urgent is CVE-2018-15836?

Priority 50/100. High severity; Remotely exploitable, no login, no user action

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References

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