High · CVSS 8.2CVE-2026-103601

CcmBlockCipher and KCcmBlockCipher leave unverified plaintext in the output buffer after a failed tag check

Answer in brief

CVE-2026-103601 records a High severity (CVSS 8.2) vulnerability in CcmBlockCipher and KCcmBlockCipher leave unverified plaintext in the output buffer after a failed tag check. The current sources do not mark it as known exploited. The current feed maps Legion of the Bouncy Castle Inc./BouncyCastle.Cryptography (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 2, 2026Updated Oct 2, 2026Source checked Oct 2, 2026First seen by HOL Oct 2, 2026Material review Oct 2, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 8.2
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 8.2. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Legion of the Bouncy Castle Inc./BouncyCastle.Cryptography (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Legion of the Bouncy Castle Inc./BouncyCastle.Cryptographygeneric	>=0 <2.7.0	2.7.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for Legion of the Bouncy Castle Inc./BouncyCastle.Cryptography.
Review the reported fix. Update Legion of the Bouncy Castle Inc./BouncyCastle.Cryptography to 2.7.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Oct 2, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 2, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 2, 2026

Sources and claim methodology

Upstream source description

Release of unverified plaintext in the CCM (CcmBlockCipher) and DSTU 7624 CCM (KCcmBlockCipher) AEAD modes in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker to obtain decryptions of ciphertexts of their choosing via forged messages sent to an application that lets the output buffer of a failed decryption be observed, for example through buffer reuse or logging, because decryption wrote the recovered plaintext into the caller-supplied output buffer before checking the authentication tag and left it there when the check failed. Only decryption into a caller-supplied buffer is affected; methods that return a newly allocated array are not.

Quoted source text, attributed separately from HOL analysis.