CVE-2026-74466 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
s390/zcrypt: Close speculative mem read possibility
The domain value is extracted from a given CCA or EP11 ioctl struct when a CPRB is about to be sent. Thus this is a user controlled value. Under some special conditions (custom device node used, administrative load) this value is used as an array index after bounds checking, but without speculation barrier.
Add the missing array_index_nospec() call to prevent speculative execution where this domain value is used.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability in question affects the Linux kernel's s390/zcrypt subsystem, specifically addressing a speculative memory read possibility that could potentially lead to information disclosure or privilege escalation. This issue arises within the cryptographic hardware acceleration framework that supports CCA (Cryptographic Coprocessor Architecture) and EP11 (Encryption Processing 11) operations on IBM z Systems platforms. The vulnerability stems from improper handling of user-controlled data during the processing of ioctl requests that interact with cryptographic coprocessors.
The technical flaw occurs when extracting a domain value from a CCA or EP11 ioctl structure prior to sending a CPRB (Cryptographic Processing Request Block). This domain value, which originates from user-space input, is subsequently used as an array index after performing bounds checking operations. However, the critical omission lies in the absence of a proper speculation barrier mechanism that would prevent speculative execution attacks from exploiting this indexed memory access. The vulnerability manifests when custom device nodes are used in conjunction with administrative load conditions, creating a scenario where the unchecked domain value can be leveraged to perform out-of-bounds memory accesses through speculative execution techniques.
The operational impact of this vulnerability extends beyond simple information disclosure, as it represents a potential pathway for attackers to exploit speculative execution side channels such as those described in the Spectre variant 1 (CVE-2017-5753) and related vulnerabilities. The lack of proper bounds checking combined with insufficient speculation barriers creates an environment where malicious actors could potentially infer sensitive information from memory locations that should remain protected, particularly when operating under administrative load conditions that may alter the system's memory access patterns.
The mitigation strategy involves implementing the missing array_index_nospec() function call which serves as a crucial barrier against speculative execution attacks by preventing the processor from speculatively reading memory locations based on potentially malicious array indices. This solution aligns with established security practices for mitigating side-channel vulnerabilities and corresponds to the CWE-128 specification for Out-of-bounds Read conditions. The fix directly addresses the ATT&CK technique T1059.001 which involves executing malicious code through kernel exploits, and more specifically targets the mitigation of speculative execution attacks that could be used to bypass traditional memory protection mechanisms.
The resolution demonstrates the importance of proper input validation and speculation barrier implementation in kernel space operations, particularly when dealing with hardware-specific cryptographic accelerators where user-controlled inputs can directly influence memory access patterns. This vulnerability highlights the critical need for comprehensive security testing of kernel subsystems that handle cryptographic operations, as even seemingly benign data processing functions can become attack vectors when insufficient protections are implemented against modern speculative execution techniques. The fix ensures that the s390/zcrypt driver properly handles user-controlled domain values through appropriate bounds checking and speculation barriers, thereby preventing potential information leakage or privilege escalation attacks that could compromise the security of cryptographic operations on IBM z Systems platforms.
This vulnerability represents a classic example of how kernel-level security can be compromised through insufficient attention to speculative execution attack surfaces, particularly in specialized hardware acceleration drivers. The solution emphasizes the importance of following established security frameworks and industry best practices for mitigating side-channel vulnerabilities, ensuring that cryptographic operations maintain their confidentiality and integrity properties even under adversarial conditions where attackers may attempt to exploit speculative execution behaviors.