PatchSiren cyber security CVE debrief

CVE-2024-42305 Siemens CVE debrief

A vulnerability in the Linux kernel's ext4 filesystem implementation has been identified, affecting Siemens SIMATIC S7-1500 TM MFP industrial control systems that utilize the GNU/Linux subsystem. The issue involves insufficient validation of directory entry structures (specifically the dot and dotdot entries) before converting a directory to indexed format using htree (directory indexing). This validation gap could lead to filesystem corruption or denial of service conditions when malformed directory structures are processed. The vulnerability was disclosed in April 2024 and remains unpatched as of the latest advisory update in September 2025, with Siemens and CISA providing mitigation guidance rather than a software fix. The affected product is an industrial programmable logic controller with an embedded GNU/Linux subsystem, commonly deployed in manufacturing and critical infrastructure environments.

Vendor: Siemens
Product: SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
CVSS: MEDIUM 5.5
CISA KEV: Not listed in stored evidence
Original CVE published: 2024-04-09
Original CVE updated: 2026-05-14
Advisory published: 2024-04-09
Advisory updated: 2026-05-14

Who should care

Industrial control system operators, OT security teams, and manufacturing infrastructure administrators using Siemens SIMATIC S7-1500 TM MFP controllers should prioritize this vulnerability. Organizations in critical infrastructure sectors (energy, water, manufacturing) with deployed S7-1500 systems need to assess their exposure, particularly if the GNU/Linux subsystem is enabled and accessible. Security teams should coordinate with plant engineers to implement access restrictions and monitor for vendor patch availability.

Technical summary

The vulnerability exists in the ext4 filesystem driver's directory indexing (htree) implementation. When converting a standard directory to an indexed directory (dx_root), the kernel fails to properly validate the presence and correctness of the dot ('.') and dotdot ('..') directory entries. These entries are fundamental to POSIX directory structure and must exist at specific offsets. Without validation, a malformed or corrupted directory could trigger unexpected behavior during the indexing operation. The fix in upstream Linux adds explicit checks for these entries before proceeding with directory indexing operations. On affected Siemens systems, exploitation requires local access to the GNU/Linux subsystem with sufficient privileges to perform filesystem operations.

Defensive priority

medium

Recommended defensive actions

Restrict interactive shell access to the GNU/Linux subsystem to trusted personnel only
Implement application whitelisting by building and running only applications from trusted sources
Monitor for anomalous filesystem operations or directory structure modifications on affected systems
Apply defense-in-depth strategies per CISA ICS recommended practices until a vendor patch becomes available
Review and implement Siemens security advisory SSA-265688 guidance when updates are released

Evidence notes

The vulnerability description indicates a kernel-level filesystem issue resolved in upstream Linux, but the Siemens product-specific advisory (ICSA-24-102-01) explicitly states 'Currently no fix is available' for the affected SIMATIC S7-1500 TM MFP GNU/Linux subsystem. The CVSS 3.1 vector (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) confirms local attack vector with low complexity, requiring low privileges, resulting in high availability impact. The advisory has undergone ten revision cycles between April 2024 and September 2025, with this CVE added in the March 2025 update (Additional Release 4).

Official resources

public