CVE-2026-16000 — KCcmBlockCipher (DSTU 7624 CCM) tag not bound to nonce when no associated data is used
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.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.3% (30-day exploitation probability)+2
- Technical severity (high)+6
- Automatable exploitation (SSVC)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Legion of the Bouncy Castle Inc. Bc-csharp).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Legion of the Bouncy Castle Inc. | Bc-csharp | < 2.7.0 | Vulnerable | CVE Program (cve.org) e CISA ADP |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 8.7 | CVSS 4.0 | High | — | — | 91579145-5d7b-4cc5-b925-a0262ff19630 via NIST National Vulnerability Database |
| 8.7 | CVSS 4.0 | High | — | — | bcorg via CVE Program (cve.org) e CISA ADP |
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X (score shown at the top: 91579145-5d7b-4cc5-b925-a0262ff19630) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · legion of the bouncy castle inc./bc-csharp
- SSVC assessment updated
- Record published
- CVSS changed · 8.7
- Source status changed · → Undergoing Analysis
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 15, 2026 – Oct 15, 2026
References
2 on the record
Elsewhere on this site
Related CVEs (same products)
- High CVE-2026-63578 Unbounded PBE iteration count when decrypting PKCS#8 private keys 13d
- High CVE-2026-63572 Unbounded MAC and bag-decryption iteration counts when loading PKCS#12 files 13d
- High CVE-2026-63575 PKCS#12 key derivation loops about 2^32 times on a zero or negative iteration count 13d
- High CVE-2026-63573 Bleichenbacher padding oracle in CMS RSA PKCS#1 v1.5 key-transport unwrap 13d
- High CVE-2026-63574 Unbounded allocation from OpenPGP signature and user attribute subpacket lengths 13d
- High CVE-2026-63576 URI name constraints checked against a mis-parsed host 13d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-16000 is "KCcmBlockCipher (DSTU 7624 CCM) tag not bound to nonce when no associated data is used", rated High. It affects Bc-csharp (Legion of the Bouncy Castle Inc.); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 8.7 describes technical severity. EPSS 0.25% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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