VulnTideExploited vulnerabilities, by vendor. Data as of .
Not in CISA KEVPublished CVSS 9.3 criticalEPSS 0.3% probability of exploitation in 30 daysFound by AI: Anthropic (Claude)
Legion of the Bouncy Castle

CVE-2026-59638: JSSE hostname verifier CN-fallback enabled by default despite documented opt-in

Is it exploited?

Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of . If CISA adds it, this page shows it as known exploited.

How likely is exploitation in the next 30 days?
0.3%

EPSS score, percentile 28.1 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?
9.3 Critical

CVSS v4.0 base score, given by the CNA

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (3)

Which versions are affected?

Affected

  • from 1.61 to before 1.85
  • from 2.73.0 to before 2.73.12
  • from 1.0.7 to before 1.0.24
  • from 2.0.0 to before 2.0.24
  • from 2.1.0 to before 2.1.24

Versions by product

Source: CISA KEV 2026.10.29, as of ; FIRST EPSS, as of ; CVE List, as of . About the data.

What to do

Advisories and patches

This summary is based on the CVE record as of . Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

As listed in the CVE record.

Legion of the Bouncy Castle Inc. BC-JAVA
StatusVersions
Affectedfrom 1.61 to before 1.85

Versions not listed are: unaffected.

Legion of the Bouncy Castle Inc. BC-LTS-JAVA
StatusVersions
Affectedfrom 2.73.0 to before 2.73.12

Versions not listed are: unaffected.

Legion of the Bouncy Castle Inc. BC-FJA
StatusVersions
Affectedfrom 1.0.7 to before 1.0.24
Affectedfrom 2.0.0 to before 2.0.24
Affectedfrom 2.1.0 to before 2.1.24

Versions not listed are: unaffected.

Source: CVE List, as of . About the data.

About this vulnerability

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).

Summary: CVE record, as of .

  • CISA has not added CVE-2026-59638 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
  • The CVE record was published on 3 Aug 2026.
  • The CVE record carries a CVSS v4.0 base score of 9.3 (Critical), given by its CNA.
  • FIRST's EPSS model puts the probability of exploitation in the next 30 days at 0.3% (percentile 28.1), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
  • CISA's SSVC assessment in the CVE record: exploitation none, automatable yes, technical impact total.
  • The credits in the CVE record name Anthropic (Claude) as finder.

Source: CISA KEV 2026.10.29, as of ; CVE List, as of ; FIRST EPSS, as of . About the data.

Description

JSSE hostname verifier CN-fallback enabled by default despite documented opt-in

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).

Source: CVE List, as of . About the data.

Weakness

CWE-297
  • CWE-297: Improper Validation of Certificate with Host Mismatch

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record.

Timeline

DateEvent
CVE record published