Description
In Bouncy Castle for Java before 1.86, the opt-in key-size validation on CMS key-transport recipients, org.bouncycastle.cms.jcajce.JceKeyTransRecipient.setKeySizeValidation(true), never ran for a message using RFC 9709 content-encryption key derivation (id-alg-cek-hkdf-sha256). The branch that should have selected the actual content-encryption algorithm carried in the key derivation AlgorithmIdentifier's parameters compared the encrypted-key byte array against the id-alg-cek-hkdf-sha256 object identifier, a comparison between a byte array and an ASN1ObjectIdentifier that is false for every possible input, so the check fell through to a key-size lookup on the outer wrapper OID. That OID identifies a key-derivation construction rather than a cipher and has no registered key size, so the size comparison was skipped entirely. A key-transport EnvelopedData or AuthEnvelopedData whose transported, HKDF-derived content-encryption key did not match the key size of the advertised content-encryption algorithm was therefore accepted even with validation explicitly enabled, silently defeating the only mechanism the API offers for enforcing recovered key size. The recipient now dispatches on the content-encryption AlgorithmIdentifier's algorithm OID, so validation checks the recovered key against the inner content-encryption algorithm. Messages with a matching key size, non-HKDF messages, and recipients that do not enable validation are unaffected. This issue also affects Bouncy Castle for Java FIPS (BC-FJA) before bcpkix-fips 2.0.13 (2.0.X series) and 2.1.13 (2.1.X series).
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Legion of the Bouncy Castle | BC-JAVA | 1.78 – < 1.86 | 1.86 |
| Legion of the Bouncy Castle | BC-FJA | 2.0.7 – < 2.0.13, 2.1.0 – < 2.1.13 | 2.0.13 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | bouncycastle | 1.86-1 | — |
| Debian 13 | bouncycastle | No fix yet | — |
| Debian 12 | bouncycastle | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | bouncycastle | No fix yet | — |
| Ubuntu 26.04 LTS | bouncycastle | No fix yet | — |
Show 5 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 24.04 LTS | bouncycastle | No fix yet | — |
| Ubuntu Pro 22.04 LTS | bouncycastle | No fix yet | — |
| Ubuntu Pro 20.04 LTS | bouncycastle | No fix yet | — |
| Ubuntu Pro 18.04 LTS | bouncycastle | No fix yet | — |
| Ubuntu Pro 16.04 LTS | bouncycastle | No fix yet | — |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | bouncycastle | 1.86-150200.3.41.1 | SUSE-SU-2026:4797-1 |
| SLES 15 SP6 | bouncycastle | 1.86-150200.3.41.1 | SUSE-SU-2026:4797-1 |
| SLES 15 SP5 | bouncycastle | 1.86-150200.3.41.1 | SUSE-SU-2026:4797-1 |
| SLES 15 SP4 | bouncycastle | 1.86-150200.3.41.1 | SUSE-SU-2026:4797-1 |
Show 7 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | bouncycastle | 1.86-160000.1.1 | SUSE-SU-2026:24461-1 |
| SLES for SAP 15 SP6 | bouncycastle | 1.86-150200.3.41.1 | SUSE-SU-2026:4797-1 |
| SLES for SAP 15 SP5 | bouncycastle | 1.86-150200.3.41.1 | SUSE-SU-2026:4797-1 |
| SLES for SAP 15 SP4 | bouncycastle | 1.86-150200.3.41.1 | SUSE-SU-2026:4797-1 |
| SLES 16.0 | bouncycastle | 1.86-160000.1.1 | SUSE-SU-2026:24461-1 |
| SLE HPC 15 SP5 | bouncycastle | 1.86-150200.3.41.1 | SUSE-SU-2026:4797-1 |
| SLE HPC 15 SP4 | bouncycastle | 1.86-150200.3.41.1 | SUSE-SU-2026:4797-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | bouncycastle | 1.86-1.1 | openSUSE-SU-2026:12090-1 |
| openSUSE Leap 16.0 | bouncycastle | 1.86-160000.1.1 | openSUSE-SU-2026:22169-1 |
Advisories 5
- WID-SEC-2026-3726 Bouncy Castle für Java: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 11, 2026
- SUSE-SU-2026:24461-1 Security update for bouncycastle SUSE / openSUSE Security Updates · Nov 4, 2026
- openSUSE-SU-2026:22169-1 Security update for bouncycastle SUSE / openSUSE Security Updates · Nov 1, 2026
- SUSE-SU-2026:4797-1 Security update for bouncycastle SUSE / openSUSE Security Updates · Oct 21, 2026
- openSUSE-SU-2026:12090-1 bouncycastle-1.86-1.1 on GA media SUSE / openSUSE Security Updates · Oct 10, 2026