# CVE-2026-16000: KCcmBlockCipher (DSTU 7624 CCM) tag not bound to nonce when no associated data is used

> Attackers can forge valid ciphertexts in Bouncy Castle C# when using KCcmBlockCipher without associated data, compromising integrity.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 2 Oct 2026
- **Updated:** 2 Oct 2026
- **Also known as:** GHSA-m3jv-gj9x-qwrv

## What is CVE-2026-16000?

CVE-2026-16000 is a high-severity vulnerability in Legion of the Bouncy Castle Inc. bc-csharp, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Missing cryptographic step in the DSTU 7624 CCM mode implementation (KCcmBlockCipher) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows an attacker who can observe encrypted messages of known or chosen content to forge ciphertexts with valid authentication tags, via messages encrypted without associated data. The cause is that the G1 block, which binds the nonce, the message length and the parameter flags into the CBC-MAC, was processed only when associated data was present. Without associated data the tag was a CBC-MAC of the plaintext alone, independent of the nonce. Only applications that use KCcmBlockCipher directly and supply no associated data are affected.

Weakness: CWE-325 (Missing Cryptographic Step)

## Which versions are affected by CVE-2026-16000?

It affects 1 product.


Products: Bouncycastle Bc-Csharp.

## How do I fix CVE-2026-16000?

No fix has been published for CVE-2026-16000 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-16000 being exploited?

There is no known exploitation of CVE-2026-16000 in the wild and no public exploit code.

## Other vulnerabilities in Legion of the Bouncy Castle Inc. bc-csharp

- [CVE-2026-63569](https://insights.sbomify.com/CVE-2026-63569/): MTI/A0 DHAgreement does not validate the peer's ephemeral value (critical 9.1)
- [CVE-2026-103600](https://insights.sbomify.com/CVE-2026-103600/): Unbounded ASN.1 nesting depth causes process-terminating stack overflow (high 8.7)
- [CVE-2026-103603](https://insights.sbomify.com/CVE-2026-103603/): Unbounded HSS public key level count allows huge array allocation during signature verification (high 8.7)
- [CVE-2026-103604](https://insights.sbomify.com/CVE-2026-103604/): Quadratic-time escaping when converting X.509 distinguished names to strings (high 8.7)
- [CVE-2026-63566](https://insights.sbomify.com/CVE-2026-63566/): DTLS handshake reassembler allocates buffer from unchecked 24-bit length (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-16000 and fix it if it is affected.

What it is: CVE-2026-16000 is a high-severity vulnerability in Legion of the Bouncy Castle Inc. bc-csharp, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-16000 in the wild and no public exploit code.

Affected product: Legion of the Bouncy Castle Inc. bc-csharp. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-16000/ (Markdown: https://insights.sbomify.com/CVE-2026-16000/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-16000
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-16000
- OSV: https://osv.dev/vulnerability/CVE-2026-16000

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-16000/
Summaries are generated and may contain mistakes; the official description above is the record.