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9.3
CVE-2026-59638: Bouncy Castle Java libraries may accept wrong host names
CVE-2026-59638 · published 2 months ago
Summary
The Bouncy Castle Java security libraries can automatically fall back to using the certificate's common name when checking a server's identity, even though this behavior should be turned on manually. This could let an attacker trick the system into trusting a fake server. Update to the latest library versions or apply the recommended configuration to disable the fallback.
What to do
- Update legion of the bouncy castle inc. bc-java to version 1.85 or later.
- Update legion of the bouncy castle inc. bc-lts-java to version 2.73.12 or later.
- Update legion of the bouncy castle inc. bc-fja to version 1.0.24 or later.
- Update bouncycastle bc-java to version 1.85 or later.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| Debian:14 | debian | bouncycastle | All versions |
| – | legion of the bouncy castle inc. | bc-java | < 1.85 |
| – | legion of the bouncy castle inc. | bc-lts-java | < 2.73.12 |
| – | legion of the bouncy castle inc. | bc-fja | < 1.0.24 |
| Debian:11 | debian | bouncycastle | All versions |
| Debian:12 | debian | bouncycastle | All versions |
| Debian:13 | debian | bouncycastle | All versions |
| Ubuntu:Pro:16.04:LTS | canonical | bouncycastle | All versions |
| Ubuntu:Pro:18.04:LTS | canonical | bouncycastle | All versions |
| Ubuntu:Pro:20.04:LTS | canonical | bouncycastle | All versions |
| Ubuntu:Pro:22.04:LTS | canonical | bouncycastle | All versions |
| Ubuntu:Pro:24.04:LTS | canonical | bouncycastle | All versions |
| Ubuntu:26.04:LTS | canonical | bouncycastle | All versions |
| – | bouncycastle | bc-java |
< 1.85 cpe:2.3:a:bouncycastle:bc-java:*:*:*:*:*:*:*:* |
| – | bouncycastle | bctls-fips |
>= 1.0.0, < 1.0.24 >= 2.0.19, < 2.0.24 >= 2.1.20, < 2.1.24 cpe:2.3:a:bouncycastle:bctls-fips:*:*:*:*:*:*:*:* |
| – | bouncycastle | bouncy_castle_for_java_lts |
<= 2.73.11 cpe:2.3:a:bouncycastle:bouncy_castle_for_java_lts:*:*:*:*:*:*:*:* |
Original advisory text
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).
References
- https://github.com/bcgit/bc-java/wiki/CVE-2026-59638
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59638... Vendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-59638 Vendor Advisory
- https://www.bouncycastle.org/download/bouncy-castle-java/ URL
- https://www.bouncycastle.org/download/bouncy-castle-java-fips/ URL
- https://www.bouncycastle.org/download/bouncy-castle-java-lts/ URL
- https://github.com/bcgit/bc-lts-java Product
- https://github.com/bcgit/bc-java Product
- https://security-tracker.debian.org/tracker/CVE-2026-59638 Vendor Advisory
- https://ubuntu.com/security/CVE-2026-59638 Third Party Advisory
- https://www.cve.org/CVERecord?id=CVE-2026-59638 Third Party Advisory
- https://github.com/bcgit/bc-java/commit/5ac55351cd1a8a7184d41c96a7ee87df0770240a Patch
- https://github.com/bcgit/bc-java/commit/799bd15320a6310a447863638aa3df64acef829b Patch
- https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9059638 Third Party Advisory
Internet-facing
3 days
Internal
60 days
- Not known to be exploited
- Can be exploited automatically
- Gives an attacker full control
Type
CWE-297Improper Validation of Certificate with Host Mismatch
Timeline
Published3 Aug 2026
Updated1 Oct 2026
First seen3 Aug 2026
Sources
CVE-2026-59638 · NVD
CVE-2026-59638 · MITRE
CVE-2026-59638 · OSV
DEBIAN-CVE-2026-59638 · OSV
UBUNTU-CVE-2026-59638 · OSV
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