How severe is CVE-2018-15836?

CVE-2018-15836 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2018-15836 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (71st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2018-15836?

CVE-2018-15836 affects Xelerance Openswan. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2018-15836?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2018-15836 published?

CVE-2018-15836 was published on 2018-09-26 and last updated on 2026-06-17.

CVE-2018-15836

CVE-2018-15836 is a high-severity vulnerability in Xelerance Openswan with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-347.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (71st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-347
Affected product: Xelerance Openswan
Published: 2018-09-26
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2018-15836?: 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.
How severe is CVE-2018-15836?: CVE-2018-15836 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2018-15836 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (71st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2018-15836?: CVE-2018-15836 affects Xelerance Openswan. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2018-15836?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2018-15836 published?: CVE-2018-15836 was published on 2018-09-26 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:xelerance:openswan:*:*:*:*:*:*:*:*

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