Junglewise Threat Intelligence

CVE-2026-31447: Linux Kernel denial of service in ext4 bigalloc mount validation

CVE-2026-31447 · Severity: high · CVSS 7.8 · Published 2026-04-22

Technologies: Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP, Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Linux Kernel. Vendors: Siemens, Linux.

Executive brief

A vulnerability exists in the Linux kernel's ext4 file system driver, which is also used in certain Siemens industrial controllers. An attacker could potentially crash the system or gain unauthorized access by tricking a user or the system into mounting a specially crafted, malicious storage device. This could lead to a complete loss of system availability or the exposure of sensitive operational data.

Technical details

A vulnerability in the ext4 file system component of the Linux kernel arises from unsupported configurations of the 'bigalloc' feature. Specifically, the kernel failed to reject mount attempts for bigalloc file systems where the 's_first_data_block' field in the superblock was non-zero. This improper validation can be triggered by a local attacker providing a specially crafted disk image or physical media. The fix involves adding a check in 'fs/ext4/super.c' within the 'ext4_feature_set_ok' function to explicitly reject such geometries. The vulnerability has been addressed in multiple stable kernel branches and affects downstream products like Siemens SIMATIC S7-1500 MFP CPUs that utilize the Linux kernel.

Affected products

  • Linux Linux Kernel All versions prior to fixed stable releases (6.1, 6.6, 6.8, etc.)
  • 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

  • 2026-03-17: disclosed: Initial patch submitted by Helen Koike
  • 2026-04-22: advisory: CVE published to NVD
  • 2026-07-14: other: Siemens advisory enrichment added to CVE record

References

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