CVE-2026-74402 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
crypto: atmel-sha204a - fix blocking and non-blocking rng logic
The blocking and non-blocking paths were failing to provide valid entropy due to improper buffer management. Reading the buffer starting from byte 1, only fetch the 32 bytes of random data from the return message.
Tested on an Atmel SHA204A device.
Before (here for blocking), tests showed repeatedly reading reduced bytes. $ head -c 32 /dev/hwrng | hexdump -C 00000000 02 28 85 b3 47 40 f2 ee 00 00 00 00 00 00 00 00 |.(..G@..........| 00000010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 00000020
After, the result will be similar to the following: $ head -c 32 /dev/hwrng | hexdump -C 00000000 5a fc 3f 13 14 68 fe 06 68 0a bd 04 83 6e 09 69 |Z.?..h..h....n.i| 00000010 75 ff cf 87 10 84 3b c9 c1 df ae eb 45 53 4c c3 |u.....;.....ESL.| 00000020
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability in question affects the Linux kernel's cryptographic subsystem, specifically within the atmel-sha204a driver implementation that interfaces with hardware random number generators. This issue represents a critical flaw in entropy generation and data retrieval mechanisms that directly impacts the security posture of systems relying on hardware-based randomness. The problem manifests in improper buffer management where the driver fails to correctly extract valid random data from the hardware device, fundamentally compromising the quality and integrity of generated entropy.
The technical root cause lies in the driver's incorrect handling of data buffers when reading from the Atmel SHA204A hardware random number generator. In the blocking read path, the implementation was starting buffer reads from byte 1 instead of byte 0, effectively skipping the first byte of the response message. This misalignment resulted in the retrieval of only 32 bytes of actual random data from a larger return message, while the preceding bytes contained protocol overhead or status information that should have been properly parsed and discarded. The improper buffer management creates a systematic bias in the entropy output where the most significant portion of the hardware response becomes inaccessible to userspace applications.
The operational impact of this vulnerability extends beyond simple data corruption, as it fundamentally undermines the cryptographic security of systems relying on hardware random number generation. When applications read from /dev/hwrng expecting high-quality entropy for cryptographic operations, they receive biased or incomplete data that can lead to predictable random sequences. This weakness directly violates security principles outlined in CWE-330 and can be categorized under ATT&CK technique T1082 for system information discovery and potentially T1587 for development tools and libraries. The reduced entropy quality compromises the strength of cryptographic keys, digital signatures, and other security mechanisms that depend on unpredictable random values.
The fix implemented addresses the core buffer management issue by ensuring proper byte alignment when reading from the hardware device. This correction allows the driver to correctly extract the full 32 bytes of random data from the hardware response rather than truncating or misaligning the data extraction process. The before and after test results demonstrate this clearly, with the pre-fix output showing all zeros except for the first byte which contained protocol information, while the post-fix result shows properly randomized data across the entire 32-byte sequence. The resolution aligns with industry best practices for hardware random number generator implementations and ensures that cryptographic applications receive the entropy quality they require for secure operations.
Security implications of this vulnerability extend to any system utilizing the atmel-sha204a driver for hardware random number generation, particularly embedded systems and IoT devices that rely heavily on hardware-based entropy sources. The improper implementation could enable attackers to predict or bias random number generation in ways that compromise cryptographic security, making it essential for system administrators to apply the kernel patch immediately. This vulnerability highlights the critical importance of proper buffer management in cryptographic implementations and demonstrates how seemingly minor implementation flaws can have significant security consequences across the entire security infrastructure.