Microsoft Defender for Endpoint leaves some Linux boxes defenseless after update

PATCHES

One bug disabled the security service on restart, another blocked installation on hardened RHEL systems

Not content with broken Windows updates, Microsoft has disclosed two problems with Defender for Endpoint on Linux – one that could disable the security service after a reboot, and another that prevents updates on FIPS-enabled Red Hat Enterprise Linux 8 and 9.

The more serious problem affected versions 101.26042.0000 through 101.26042.0009 across all supported Linux operating systems. After an upgrade or reinstall followed by a reboot, “the Defender service might be disabled on some devices,” according to Microsoft.

“If you use Defender for Servers (Plan 1 or 2) with Defender for Cloud and have the MDE [Microsoft Defender Endpoint] integration enabled, automatic updates for the MDE.Linux extension are enabled by default, which means your machines could have received an affected version automatically,” it explained.

“If an affected version was installed, the issue might impact active protection on rebooted devices until remediation steps are taken.”

Microsoft did not specify what caused Defender to become disabled, but anything that could knock out endpoint protection will give administrators sweaty palms.

A separate problem affected RHEL 8 and 9 systems running in FIPS mode: the 101.26042.x update could fail to install, leaving devices on their previous version. FIPS refers to US Federal Information Processing Standards, which in this context impose requirements on the cryptography used by government and other regulated systems.

Although Microsoft’s alert did not mention an available update, its release notes direct users affected by the disabled-service bug to build 101.26042.0011. The separate FIPS installation problem is fixed in version 101.26052.0011 and later.

Microsoft Defender for Endpoint on Linux protects server workloads on-premises and in the cloud. According to Microsoft, “it helps you prevent, detect, investigate, and respond to advanced threats with unified visibility through the Microsoft Defender portal.”

Other endpoint security platforms are available, but where an organization has gone all-in with Microsoft, the unified management offered by Defender for Endpoint on Linux can be difficult to resist.

Microsoft has an unfortunate habit of shipping broken updates for its flagship operating system, Windows. An update that breaks software specifically designed to protect a device takes things to another level, particularly given the relentless rise in attacks and the need to both fend them off and monitor activity. Hence the appeal of unified visibility through the Microsoft Defender portal.

However, an update that could leave Defender disabled after a reboot – while also refusing to install on some security-hardened systems – is less than ideal. ®