CVE-2026-59646 DTLS handshake reassembler allocates buffer from unchecked 24-bit length

What is CVE-2026-59646?

CVE-2026-59646 is a high-severity denial of service vulnerability in Bouncycastle Bc-Java, published on 3 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

In Bouncy Castle for Java before 1.85, DTLS handshake reassembler allocates buffer from unchecked 24-bit length. 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).

Weakness: CWE-789

Which versions are affected by CVE-2026-59646?

It affects 3 products.

Products include Bouncycastle Bc-Java, Bouncycastle Bctls-Fips, Bouncycastle Bouncy Castle for Java Lts.

How do I fix CVE-2026-59646?

Upgrade to a fixed version.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-59646 being exploited?

There is no known exploitation of CVE-2026-59646 in the wild and no public exploit code.

Other vulnerabilities in Bouncycastle Bc-Java

• CVE-2007-6721 Legion of the Bouncy Castle Java Cryptography API Bleichenbacher Oracle Vulnerability Critical 10.0
• CVE-2018-1000613 Deserialization of Untrusted Data in Bouncy castle Critical 9.8
• CVE-2026-58062 Stapled OCSP response accepted without binding to the checked certificate Critical 9.3
• CVE-2026-59638 JSSE hostname verifier CN-fallback enabled by default despite documented opt-in Critical 9.3
• CVE-2026-59650 MTI/A0 DH agreement exponentiates unvalidated peer value Critical 9.3

All Bouncycastle Bc-Java vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as CLEANSTART-2026-TX54666, DEBIAN-CVE-2026-59646, GHSA-4m8h-6737-hrw6, UBUNTU-CVE-2026-59646.