ICS Patch Tuesday: Schneider Electric, Siemens Fix Critical Flaws

CVE-2026-31431 ('Copy Fail') is an incorrect resource transfer between spheres (CWE-669/CWE-1288) in the Linux kernel's algif_aead implementation of the AF_ALG userspace crypto interface, introduced roughly nine years ago (around 2017, per public reporting) when commit 72548b093ee3 switched AEAD operations to in-place handling even though the source and destination buffers come from different mappings. A local, unprivileged user can trigger the flaw by performing AEAD operations through the AF_ALG socket interface, causing the kernel to mishandle the copy of ciphertext and associated data. Successful exploitation provides a reliable local privilege escalation to root (C:H/I:H/A:H per the CVSS vector). Nearly every major Linux distribution and enterprise platform is exposed, including the kernel itself, Red Hat Enterprise Linux (including AUS, EUS, TUS and Update Services for SAP Solutions), OpenShift Container Platform, Amazon Linux, Ubuntu, Debian, openSUSE Leap, SUSE CaaS Platform, NixOS, and Linux-based products from Arista and Siemens. The flaw has public proof-of-concept code, a 99.9% EPSS score, and was added to CISA's Known Exploited Vulnerabilities catalog on 2026-05-01, indicating exploitation in the wild (ransomware use is unknown).

Do: Patch by installing the kernel update for CVE-2026-31431 through your distribution's security channel (Red Hat Enterprise Linux including AUS/EUS/TUS/SAP channels, OpenShift, Amazon Linux, Ubuntu, Debian, openSUSE Leap, SUSE CaaS Platform, NixOS, and Arista/Siemens firmware/software as applicable) and reboot into the patched kernel; the data provides no fixed version numbers, so defer to vendor advisories. Because the flaw is in CISA's KEV catalog (added 2026-05-01) with a 99.9% EPSS score, prioritize internet-reachable and multi-user systems first and follow BOD 22-01 guidance for cloud services. Check running kernel versions ('uname -r') and distribution advisory status to confirm you are on a fixed build.

CVE-2026-3869 is a critical (CVSS 4.0 score 9.2) incorrect implementation of an authentication algorithm (CWE-303) in a Schneider Electric programmable logic controller (PLC), disclosed and patched as part of Schneider Electric's ICS Patch Tuesday release. The flaw is reachable over the network with no privileges or user interaction required, but it carries elevated attack requirements: it comes into play when the PLC is running an application project with a lower application level, which is the configuration precondition for exploitation. An attacker who meets those conditions can defeat the controller's authentication mechanism and cause a complete loss of confidentiality, integrity and availability of the PLC (VC:H/VI:H/VA:H), meaning they could read, modify or disrupt the running control process. Affected users are operators of the impacted Schneider Electric PLC line; the available data does not name the specific model or firmware versions, so operators should confirm their exposure against the official Schneider notification. No public proof-of-concept is known and the flaw is not listed in CISA's KEV, with no reports of exploitation in the wild to date.

Do: Check the Schneider Electric security notification for CVE-2026-3869 to confirm whether your PLC model and firmware fall in the affected range, and apply the vendor's published firmware update. Until patched, restrict exposure by firewalling or allowlisting the PLC's management and protocol ports and keeping OT networks segmented, and verify whether the controller is running an application project with a lower application level, since that configuration is the precondition for exploitation.