TI-2026-65842 Aliases CVE-2026-63567 GHSA-6w4x-4wpp-m6r4

IesEngine block-cipher mode checks padding before MAC (CBC padding oracle)

LOW 36CWE-203Published 2026-10-02 · Updated 2026-10-02

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Attack requirements: Present
Impact type: Information disclosure
Confidentiality · integrity · availability: High · None · None
Fix status: Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-203.

Summary

Observable discrepancy in IesEngine.DecryptBlock in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who has captured an IES or ECIES ciphertext, and who can submit modified ciphertexts for decryption under the same key pair, to recover its plaintext via a CBC padding-oracle attack, because in block-cipher mode the engine decrypts the ciphertext and removes its padding before verifying the MAC. A padding failure is therefore reported with a different error message, and without the MAC computation, compared with a MAC failure. Only applications that construct IesEngine directly with a padded block cipher, such as AES in CBC mode with PKCS#7 padding, are affected; stream-mode IES is not.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00453 39th percentileScored 2026-11-07

Fix Fixed bc-csharp (Legion of the Bouncy Castle Inc.): 2.7.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
Legion of the Bouncy Castle Inc.	bc-csharp	before 2.7.0	2.7.0	Patch available	CNA

bc-csharp VendorLegion of the Bouncy Castle Inc. Affected before 2.7.0 Fixed in 2.7.0 Patch available CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:bouncycastle:bc-csharp::::::::	before 2.7.0	Vulnerable	Legion of the Bouncy Castle Inc.

cpe:2.3:a:bouncycastle:bc-csharp:*:*:*:*:*:*:*:* Versions before 2.7.0 Vulnerable ·Legion of the Bouncy Castle Inc.

Remediation

Fix · CNA bc-csharp (Legion of the Bouncy Castle Inc.) Fixed in 2.7.0

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

Release · 2026-10-02
Legion of the Bouncy Castle bc-csharp 2.7.0
21 records Highest priority Priority MEDIUM 8 MEDIUM, 13 LOW
Other records, highest priority first
- TI-2026-65844 MTI/A0 DHAgreement does not validate the peer's ephemeral valuePriority MEDIUM 47
- TI-2026-66020 Unbounded HSS public key level count allows huge array allocation during signature verificationPriority MEDIUM 44
- TI-2026-66017 Unbounded ASN.1 nesting depth causes process-terminating stack overflowPriority MEDIUM 44
Show all 21 records →

Timeline

2026-10-02 Threatist record created from CVE-2026-63567
2026-10-03 Alias added: GHSA-6w4x-4wpp-m6r4
2026-10-27 CVSS score added · NVD

References

Patch 3

TI-2026-65844 MTI/A0 DHAgreement does not validate the peer's ephemeral value CVSS 4.0CRITICAL 9.1
TI-2026-66020 Unbounded HSS public key level count allows huge array allocation during signature verification CVSS 4.0HIGH 8.7
TI-2026-66017 Unbounded ASN.1 nesting depth causes process-terminating stack overflow CVSS 4.0HIGH 8.7
TI-2026-65849 Unbounded allocation from OpenPGP signature and user attribute subpacket lengths CVSS 4.0HIGH 8.7
TI-2026-65843 Unbounded CMP/CRMF password-based MAC iteration count allows CPU exhaustion CVSS 4.0HIGH 8.7
TI-2026-65841 DTLS handshake reassembler allocates buffer from unchecked 24-bit length CVSS 4.0HIGH 8.7

See all 21 →

Sources

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