PatchSiren cyber security CVE debrief

CVE-2025-21844 Siemens CVE debrief

A vulnerability in the SMB client implementation within the GNU/Linux subsystem of Siemens SIMATIC S7-1500 TM MFP could allow a local, authenticated attacker to cause a denial-of-service condition. The issue stems from a missing null pointer check for `next_buffer` in the `receive_encrypted_standard()` function, which may lead to a crash when processing malformed SMB encrypted responses. The vulnerability requires local access and low privileges, with no confidentiality or integrity impact, but high availability impact.

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 asset owners using Siemens SIMATIC S7-1500 TM MFP with the GNU/Linux subsystem enabled should prioritize this vulnerability. Organizations with remote or shared access to the controller's Linux environment face elevated risk of accidental or intentional denial-of-service.

Technical summary

The vulnerability exists in the Linux kernel SMB client implementation used by the GNU/Linux subsystem of Siemens SIMATIC S7-1500 TM MFP. The `receive_encrypted_standard()` function fails to validate the `next_buffer` pointer before dereferencing it, potentially causing a kernel crash when processing crafted SMB encrypted responses. This is classified as CWE-476 (NULL Pointer Dereference). The attack requires local access with low privileges and does not provide confidentiality or integrity compromise, but can render the system unavailable.

Defensive priority

medium

Recommended defensive actions

Restrict interactive shell access to the GNU/Linux subsystem to trusted personnel only
Implement application whitelisting to ensure only trusted applications are built and executed
Monitor for anomalous SMB client activity on affected systems
Apply vendor patches when available per Siemens security advisory SSA-265688
Segment affected industrial control systems from untrusted networks

Evidence notes

The vulnerability description indicates a missing validation check in SMB client code. 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 attack complexity and low privileges required, resulting in high availability impact only. The affected product is specifically the GNU/Linux subsystem of the Siemens SIMATIC S7-1500 TM MFP industrial controller.

Official resources

2024-04-09