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CVE-2026-59638

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

MEDIUM
6.5
CVSS Score
Published: August 3, 2026 at 12:57 AM UTC
Updated: August 28, 2026 at 05:42 PM UTC
5 products affected across 2 vendorsBc JavaBouncy Castle for Java LtsBctls Fips

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Severity
MEDIUM6.5
Exploit prediction
EPSS 0.3%
SSVC
No known exploit

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).

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Bc Java· Bouncycastle
95%
v < 1.85
Affected range stops below 1.85, so it looks safe — our inference, not a vendor statement
Bctls Fips· Bouncycastle
95%
1.0.0 ≤ v < 1.0.242.0.19 ≤ v < 2.0.242.1.20 ≤ v < 2.1.24
Affected range stops below 1.0.24, so it looks safe — our inference, not a vendor statement
Affected range stops below 2.0.24, so it looks safe — our inference, not a vendor statement
Affected range stops below 2.1.24, so it looks safe — our inference, not a vendor statement
Bouncy Castle for Java Lts· Bouncycastle
95%
v ≤ 2.73.11
Bouncy Castle for Java FIPS (BC-FJA)· Legion of Bouncy Castlemaven
60%
1.0.7 ≤ v < 1.0.242.0.0 ≤ v < 2.0.242.1.0 ≤ v < 2.1.241.0.72.0.02.1.0
Affected range stops below 1.0.24, so it looks safe — our inference, not a vendor statement
Affected range stops below 2.0.24, so it looks safe — our inference, not a vendor statement
Affected range stops below 2.1.24, so it looks safe — our inference, not a vendor statement
BC Java· Legion of Bouncy Castlemaven
60%
1.61 ≤ v < 1.852.73.0 ≤ v < 2.73.121.612.73.0
Affected range stops below 1.85, so it looks safe — our inference, not a vendor statement
Affected range stops below 2.73.12, so it looks safe — our inference, not a vendor statement

References (4)

Source: cverecord
https://github.com/bcgit/bc-java/wiki/CVE-2026-59638
Patch
Source: cverecord
https://github.com/bcgit/bc-java/commit/799bd15320a6310a447863638aa3df64acef829b
Patch
Source: cverecord
https://github.com/bcgit/bc-java/commit/5ac55351cd1a8a7184d41c96a7ee87df0770240a
Vendor AdvisoryThird Party Advisory
Source: cverecord
https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9059638

SSVC — Action Prioritization

SSVCNo known exploitAutomatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.5MEDIUM[email protected]
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusANALYZED
CWE
CWE-297

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