---
cve: "CVE-2026-15999"
severity: "HIGH"
cvss: 8.2
epss: "0.2%"
vendor: "Legion of the Bouncy Castle Inc."
kev: false
exploited: false
published: "2026-10-02 06:52:16"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-10-24T06:51:11+02:00"
---

# CVE-2026-15999

> 8.2 HIGH · 🧪 PoC

## Beschreibung

Improper validation of integrity check value in the AES-CCM implementation (CcmParameters and CcmBlockCipher) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows an on-path attacker to modify CCM-encrypted content without detection via an AlgorithmIdentifier whose CCMParameters declare an authentication tag (aes-ICVlen) of zero or another length outside the RFC 5084 set, because CcmParameters accepted any value and CcmBlockCipher validated the tag length only when encrypting, so decryption compared a zero-length or very short tag. Affected paths include ParameterUtilities.GetCipherParameters, used by CmsEnvelopedData and CmsEnvelopedDataParser for EnvelopedData encrypted with AES-CCM, and any caller passing an unchecked tag length to CcmBlockCipher for decryption.

## CNA-Record (Kanon, cvelistV5)

- CNA: **bcorg**
- State: PUBLISHED
- Stand: 2026-10-02 18:02:14
- CNA-CVSS: **8.2** (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)

## CISA-Anreicherung (vulnrichment/ADP)

- CISA-SSVC (Coordinator, v2.0.3):
  - Exploitation: **none**
  - Automatable: **no**
  - Technical Impact: **partial**

## CVSS-Vektor

```
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |

## Schwachstellen-Klasse

- **CWE-354** — Improper Validation of Integrity Check Value
  The product does not validate or incorrectly validates the integrity check values or "checksums" of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission.

## Angriffsmuster (CAPEC)

- [CAPEC-75 — Manipulating Writeable Configuration Files](https://capec.mitre.org/data/definitions/75.html) _(Severity: Very High)_
- [CAPEC-145 — Checksum Spoofing](https://capec.mitre.org/data/definitions/145.html) _(Severity: Medium)_
- [CAPEC-463 — Padding Oracle Crypto Attack](https://capec.mitre.org/data/definitions/463.html) _(Severity: High)_

## Patch verfügbar (OSV)

- 4007498b13582d90ee1eda5d9920c324428b98b3 (Commit)
- 2818bdfa55efd58b0d6a1c75f360b8404d879780 (Commit)

## BSI-Hinweise (deutsch)

- [Bouncy Castle: Mehrere Schwachstellen](https://wid.cert-bund.de/portal/wid/sicherheitshinweis/WID-SEC-W-2026-3713) — _BSI-Einstufung: mittel_
  Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Bouncy Castle ausnutzen, um Sicherheitsvorkehrungen zu umgehen, Daten zu manipulieren oder offenzulegen und einen Denial-of-Service-Zustand auszulösen.

## Referenzen

- <https://github.com/bcgit/bc-csharp/wiki/CVE-2026-15999>
- <https://github.com/bcgit/bc-csharp/commit/2818bdfa55efd58b0d6a1c75f360b8404d879780>
- <https://github.com/bcgit/bc-csharp/commit/9d284d8f379614def853b590c62bbb31c48f7af0>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/sicherheitsluecken/cve-2026-15999/) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI WID (CSAF)_