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libkcapi CVE-2026-71225

| EUVDEUVD-2026-53336 MEDIUM
Use of Insufficiently Random Values (CWE-330)
2026-08-05 redhat GHSA-qv62-qmw8-96h9
Information Disclosure Red Hat Enterprise Linux 10 Red Hat Enterprise Linux 8 Red Hat Enterprise Linux 9 Red Hat Hardened Images Red Hat Openshift Container Platform 4
6.5
CVSS 3.1 · NVD
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Severity by source

Vendor (redhat) PRIMARY
MEDIUM
qualitative
NVD
6.5 MEDIUM
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
vuln.today AI
6.5 MEDIUM

AV:N for indirect network exploitation via crafted app inputs; AC:H for the strict one-shot API, >64KiB, stateful-mode prerequisite; C:H for IV-reuse enabling plaintext recovery; I:L per description's integrity processing error note.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative
Red Hat
6.5 MEDIUM
qualitative

Primary rating from Vendor (redhat).

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
Low
Availability
None

Lifecycle Timeline

2
Analysis Generated
Aug 05, 2026 - 13:16 vuln.today
CVE Published
Aug 05, 2026 - 12:16 cve.org
MEDIUM 6.5

DescriptionNVD

A flaw was found in libkcapi. When performing one-shot symmetric cipher operations on large inputs (over 64 KiB) in stateful modes such as Counter (CTR) or Cipher Block Chaining (CBC), the library improperly reuses the Initialization Vector (IV) for each internal data chunk. A remote attacker could potentially exploit this by making an application that uses libkcapi process specially crafted large inputs. This can lead to a significant weakening of data confidentiality, as the repeated IV use can expose relationships in encrypted plaintext, and may also affect data integrity by causing incorrect cryptographic processing.

AnalysisAI

IV reuse in libkcapi's one-shot symmetric cipher operations allows a remote attacker to weaken data confidentiality for applications processing inputs larger than 64 KiB under stateful modes (CTR or CBC). Affected deployments include Red Hat Enterprise Linux 8, 9, and 10, Red Hat Hardened Images, and OpenShift Container Platform 4. No public exploit or active exploitation has been identified; the AV:N vector reflects an indirect attack path where an adversary induces a vulnerable application to process specially crafted oversized inputs, enabling ciphertext analysis to expose plaintext relationships or recover data.

Technical ContextAI

libkcapi is a userspace C library providing a high-level interface to the Linux kernel's AF_ALG crypto API (kcapi). Its one-shot cipher API is designed to encrypt or decrypt an entire buffer in a single call. Internally, when a buffer exceeds 64 KiB, libkcapi splits the payload into kernel-sized chunks for submission via splice/sendmsg. The flaw is that the original IV is reused for each chunk rather than maintaining cryptographic state across chunk boundaries - in CTR mode this means the counter is not advanced, and in CBC mode the last ciphertext block is not fed forward as the IV for the next chunk. CWE-330 (Use of Insufficiently Random Values) captures the root cause: the IV, which must be unique or stateful per the mode's contract, is effectively treated as static across chunks. In CTR mode, IV reuse with any known plaintext enables direct XOR-based plaintext recovery for subsequent blocks; in CBC mode, it breaks semantic security and reveals repeated plaintext patterns.

RemediationAI

Apply the updated libkcapi package from Red Hat when released via the advisory at https://access.redhat.com/security/cve/CVE-2026-71225. No exact patched package version is confirmed from available data - the patch availability status should be verified directly against the Red Hat Bugzilla entry https://bugzilla.redhat.com/show_bug.cgi?id=2462011. As immediate compensating controls, application developers using libkcapi should replace one-shot cipher calls for inputs exceeding 64 KiB with streaming (multi-call) cipher APIs that maintain IV state across operations, or decompose large inputs into chunks of 64 KiB or fewer at the application layer with explicit IV advancement per chunk. Migrating to AEAD modes (e.g., AES-GCM via kcapi_aead_*) eliminates IV-statefulness concerns entirely but requires application-level API changes and cipher renegotiation with peers. Organizations with strict cryptographic integrity requirements should audit all codepaths invoking kcapi_cipher_enc/dec or equivalent one-shot functions on potentially large buffers.

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise Micro 5.3 Not-Affected
SUSE Linux Enterprise Micro 5.4 Not-Affected
SUSE Linux Enterprise Micro 5.5 Not-Affected

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CVE-2026-71225 vulnerability details – vuln.today
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