How severe is CVE-2026-59638?

CVE-2026-59638 has a CVSS 4.0 base score of 9.3, rated critical severity.

Is CVE-2026-59638 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (20th percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-59638?

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

When was CVE-2026-59638 published?

CVE-2026-59638 was published on 2026-08-03 and last updated on 2026-08-04.

CVE-2026-59638

CVE-2026-59638 is a critical-severity vulnerability with a CVSS 4.0 base score of 9.3. 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-297.

Key facts

Severity: Critical (CVSS 4.0 base score 9.3)
EPSS exploit prediction: 0% (20th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-297
Published: 2026-08-03
Last modified: 2026-08-04

Description

In Bouncy Castle for Java before 1.85, JSSE hostname verifier CN-fallback enabled by default despite documented opt-in. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bctls-fips 1.0.24 (1.0.X series), 2.0.24 (2.0.X series) and 2.1.24 (2.1.X series).

Frequently asked questions

What is CVE-2026-59638?: In Bouncy Castle for Java before 1.85, JSSE hostname verifier CN-fallback enabled by default despite documented opt-in. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bctls-fips 1.0.24 (1.0.X series), 2.0.24 (2.0.X series) and 2.1.24 (2.1.X series).
How severe is CVE-2026-59638?: CVE-2026-59638 has a CVSS 4.0 base score of 9.3, rated critical severity.
Is CVE-2026-59638 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (20th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-59638?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2026-59638 published?: CVE-2026-59638 was published on 2026-08-03 and last updated on 2026-08-04.

References

Other CWE-297 vulnerabilities

CVE-2025-46408 — Critical (CVSS 9.8): An issue was discovered in the methods push.lite.avtech.com.AvtechLib.GetHttpsResponse and…
CVE-2026-15925 — Critical (CVSS 9.2): Improper TLS hostname verification in Snowflake Connector for Python versions prior to 4.7.1 and 3.18.1 may have…
CVE-2026-48144 — Critical (CVSS 9.1): Improper Validation of Certificate with Host Mismatch vulnerability in Apache Thrift c_glib bindings. This issue…
CVE-2025-68637 — Critical (CVSS 9.1): The Uniffle HTTP client is configured to trust all SSL certificates and disables hostname verification by default.…
CVE-2026-35563 — High (CVSS 8.5): It was identified that the LDAP client implementation in version 2.1.7 does not verify if the server certificate…
CVE-2025-3501 — High (CVSS 8.2): A flaw was found in Keycloak. By setting a verification policy to 'ALL', the trust store certificate verification is…

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