# CVE-2026-31628: Linux Kernel information disclosure in AMD Zen1 hardware divider

Source: https://junglewise.ai/threats/cve-2026-31628-linux-kernel-information-disclosure-in-amd-zen1-hardware-divider  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-24. Updated: 2026-07-14  
License: CC BY 4.0 with a link back

CVE-2026-31628 · Severity: medium · CVSS 5.5 · Published 2026-04-24

A hardware flaw in AMD Zen1 processors, used in various computing systems and industrial controllers, could allow sensitive data to leak between different programs or users. The processor's hardware divider may fail to clear data from previous calculations, potentially allowing an attacker to observe information they should not have access to. This issue affects the Linux kernel and specific Siemens industrial CPUs that utilize these processors.

Technologies: [Linux Kernel](https://junglewise.ai/threats/technologies/kernel), [Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP](https://junglewise.ai/threats/technologies/simatic-s7-1500-cpu-1518-4-pn-dp-mfp), [Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP](https://junglewise.ai/threats/technologies/simatic-s7-1500-cpu-1518f-4-pn-dp-mfp), [Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP](https://junglewise.ai/threats/technologies/siplus-s7-1500-cpu-1518-4-pn-dp-mfp). Vendors: [Linux](https://junglewise.ai/threats/vendors/linux), [Siemens](https://junglewise.ai/threats/vendors/siemens).

## Quick answers

**Is CVE-2026-31628 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-31628 being exploited in the wild.

**How severe is CVE-2026-31628?** Medium severity, with a CVSS score of 5.5, published 24 April 2026.

**Which products and versions are affected?** Linux Kernel Zen1 architectures; various stable branches patched; Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6; Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5, V3.1.6; Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6.

**Is there a fix for CVE-2026-31628?** A patch was published on 2026-04-07: Initial patch authored by AMD for Linux kernel Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-31628 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-31628?** Check whether you run Linux Kernel, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

This vulnerability stems from a hardware flaw in the AMD Zen1 architecture's floating-point hardware divider (FPDSS). Under specific conditions, the divider can retain partial results from previous operations, which can then be observed by a separate attacker-controlled thread. The fix involves setting a 'chicken bit' (MSR_AMD64_FP_CFG_ZEN1_DENORM_FIX_BIT) in the Model Specific Register (MSR) to change hardware behavior and prevent this leakage. The vulnerability is addressed in the Linux kernel via updates to arch/x86/kernel/cpu/amd.c and arch/x86/include/asm/msr-index.h. Local access is required for exploitation.

## Affected products

- Linux Linux Kernel Zen1 architectures; various stable branches patched
- Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6
- Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5, V3.1.6
- Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5, V3.1.6

## Timeline

- 2026-04-07: patched: Initial patch authored by AMD for Linux kernel
- 2026-04-24: disclosed: CVE published

## References

- [https://git.kernel.org/stable/c/0548529af20e68c6552817834b766646dd3bd7a7](https://git.kernel.org/stable/c/0548529af20e68c6552817834b766646dd3bd7a7)
- [https://git.kernel.org/stable/c/1272cfedf4cd1019ddf583917a99b62f2d3645bb](https://git.kernel.org/stable/c/1272cfedf4cd1019ddf583917a99b62f2d3645bb)
- [https://git.kernel.org/stable/c/546785c719418c6166834a47e372a88f5f7ae893](https://git.kernel.org/stable/c/546785c719418c6166834a47e372a88f5f7ae893)
- [https://git.kernel.org/stable/c/91f02726b2203b71545713ecb7fb006e60a2d66f](https://git.kernel.org/stable/c/91f02726b2203b71545713ecb7fb006e60a2d66f)
- [https://git.kernel.org/stable/c/ad17f07e95e6e8505e2153e5b391f0d27eacce25](https://git.kernel.org/stable/c/ad17f07e95e6e8505e2153e5b391f0d27eacce25)
- [https://git.kernel.org/stable/c/b731aca06387b195058a9f6449a03b62efa1bd10](https://git.kernel.org/stable/c/b731aca06387b195058a9f6449a03b62efa1bd10)
- [https://git.kernel.org/stable/c/e55d98e7756135f32150b9b8f75d580d0d4b2dd3](https://git.kernel.org/stable/c/e55d98e7756135f32150b9b8f75d580d0d4b2dd3)

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