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CVE-2026-16001— IesEngine stream-mode MAC forgery via length-dependent KDF split

Quick assessment

Affected
Legion of the Bouncy Castle Inc. bc-csharp
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 Legion of the Bouncy Castle 组织的 bc-csharp 库（版本号低于 2.7.0）中，IesEngine（一种未使用分组密码的 IesEngine）在流模式下运行存在漏洞，导致消息认证密钥通过加密密钥流暴露。该漏洞允许远程攻击者在观察到一条具有已知明文的加密消息后，构造精心设计的密文和消息认证码（MAC）标签，伪造长度更短且由攻击者任意选择的消息，而这些消息会被接收方视为合法和认证过的。这是因为 MAC 密钥直接从密钥派生输出中获取，且该派生输出紧随与消息等长的密钥流之后；而密钥派

CVSS 8.2 · High EPSS 0.17% · P6

Possible ATT&CK Techniques 2 AI

T1058 T1530 · Data from Cloud Storage

Affected Version Matrix 1

VendorProduct Version RangeStatus
Legion of the Bouncy Castle Inc. bc-csharp < 2.7.0 affected
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I. Basic Information for CVE-2026-16001

Vulnerability Information
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Vulnerability Title
IesEngine stream-mode MAC forgery via length-dependent KDF split
Source: CVE Program / CVE List V5
Vulnerability Description
Exposure of the message authentication key through the encryption keystream in the stream mode of IesEngine (an IesEngine constructed without a block cipher) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who has observed one encrypted message with known plaintext to forge shorter messages of their choosing that the recipient accepts as authentic, via a crafted ciphertext and MAC tag, because the MAC key was taken from the key derivation output directly after a keystream as long as the message, while the derivation input depends only on the static key pair and fixed parameters. The keystream revealed by that one message therefore contains the MAC key for every sufficiently shorter message.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
完整性检查值验证不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Legion of the Bouncy Castle Inc. bc-csharp 0 ~ 2.7.0 -

II. Public POCs for CVE-2026-16001

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III. Intelligence Information for CVE-2026-16001

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Other References for CVE-2026-16001 (1)

Same Patch Batch · Legion of the Bouncy Castle Inc. · 2026-10-02 · 24 CVEs total

CVE-2026-63569 9.1 CRITICAL MTI/A0 DHAgreement does not validate the peer's ephemeral value
CVE-2026-16000 8.7 HIGH KCcmBlockCipher (DSTU 7624 CCM) tag not bound to nonce when no associated data is used
CVE-2026-63566 8.7 HIGH DTLS handshake reassembler allocates buffer from unchecked 24-bit length
CVE-2026-63571 8.7 HIGH Attribute certificate path validation does not verify the attribute certificate's signatur
CVE-2026-63568 8.7 HIGH Unbounded CMP/CRMF password-based MAC iteration count allows CPU exhaustion
CVE-2026-103600 8.7 HIGH Unbounded ASN.1 nesting depth causes process-terminating stack overflow
CVE-2026-63574 8.7 HIGH Unbounded allocation from OpenPGP signature and user attribute subpacket lengths
CVE-2026-103604 8.7 HIGH Quadratic-time escaping when converting X.509 distinguished names to strings
CVE-2026-103603 8.7 HIGH Unbounded HSS public key level count allows huge array allocation during signature verific
CVE-2026-17507 8.7 HIGH MLS membership checks compare a uint32 leaf_index as signed, admitting an out-of-range sen
CVE-2026-18036 8.2 HIGH NTRU leaks private key information by reducing secret values with a non-constant-time inte
CVE-2026-63577 8.2 HIGH Name Constraints bypass: directoryName constraint matched at any position in the DN instea
CVE-2026-63576 8.2 HIGH URI name constraints checked against a mis-parsed host
CVE-2026-63573 8.2 HIGH Bleichenbacher padding oracle in CMS RSA PKCS#1 v1.5 key-transport unwrap
CVE-2026-103602 8.2 HIGH Name constraints bypass via trailing dot in rfc822Name, dNSName and URI hosts
CVE-2026-103601 8.2 HIGH CcmBlockCipher and KCcmBlockCipher leave unverified plaintext in the output buffer after a
CVE-2026-63567 8.2 HIGH IesEngine block-cipher mode checks padding before MAC (CBC padding oracle)
CVE-2026-15999 8.2 HIGH AES-CCM decryption accepts zero or out-of-range tag length, bypassing authentication
CVE-2026-63578 7.1 HIGH Unbounded PBE iteration count when decrypting PKCS#8 private keys
CVE-2026-63570 7.1 HIGH Pkcs12Store.GetCertificateChain loops forever on cyclic issuer links

Showing top 20 of 24 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: bc-csharp
Same vendor: Legion of the Bouncy Castle Inc.
Same weakness: CWE-354

V. Comments for CVE-2026-16001

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