The kernel drivers in Sophos Intercept X Advanced – Sophos News

Working in ‘kernel-space’ – probably the most privileged layer of an working system, with direct entry to reminiscence, {hardware}, useful resource administration, and storage – is vitally necessary for safety merchandise. It permits them to observe ‘user-space’ – the non-privileged surroundings the place functions run – and shield towards malware that executes in that surroundings, even when it tries to evade detection. However kernel entry additionally permits safety merchandise to counter extra insidious threats throughout the kernel itself. As we’ve reported beforehand, for instance, some menace actors use BYOVD (Carry Your Personal Weak Driver) assaults, or try and get their very own malicious drivers cryptographically signed, to be able to entry kernel-space and make the most of that elevated stage of entry.

Nonetheless, from a safety standpoint, working in kernel-space comes with its personal dangers. A flawed step on this surroundings – equivalent to a nasty replace to a kernel driver – could cause outages. If the driving force in query begins at boot time, when the working system first masses, that may result in extended impacts, probably requiring affected hosts to be began in a restoration mode to mitigate the issue and permit the machines besides usually.

Sophos’ Intercept X Superior product makes use of 5 kernel drivers as of launch 2024.2. All drivers are extensively examined* with relevant flags enabled and disabled, and shipped with new flags disabled. (Sophos Intercept X and Sophos Central use characteristic flags to progressively allow new options. Characteristic flags are deployed by Sophos Central. New options are usually ‘guarded’ by characteristic flags – turned off except the flag is enabled – in order that the characteristic might be rolled out progressively and probably revised earlier than wider enablement.)

On this article, within the pursuits of transparency, we’ll discover what these drivers are, what they do, after they begin, how they’re signed, and what their inputs are. We’ll additionally discover among the safeguards we put in place round these drivers to reduce the danger of disruption (equivalent to staged rollouts, as talked about above; we offer an instance of this later within the article), and the choices out there to clients on the subject of configuring them. It’s additionally value noting that Intercept X Superior and all its elements, together with the kernel drivers, has been a part of an exterior bug bounty program since December 14, 2017; we welcome scrutiny through exterior bug bounty submissions, and we foster a tradition of collaboration with the analysis neighborhood.

* ‘Testing’ refers to a variety of inside testing, together with Microsoft-provided instruments and verifiers

The next desk offers an at-a-glance overview of the 5 kernel drivers that are a part of Intercept X Superior launch 2024.2.

Desk 1: An summary of the kernel drivers in Intercept X Advanced2024.2
* Microsoft Home windows Early Launch Anti-malware Writer
+ Microsoft Home windows {Hardware} Compatibility Writer

Determine 1: A conceptual depiction of user-space/kernel boundaries and the place Intercept X Superior elements function

What it does: SophosEL.sys is the Sophos Early Launch Anti-Malware (ELAM) driver.

Inputs: This driver has one enter – a blocklist of known-bad drivers which should be prevented from executing as boot begin drivers at machine startup. This blocklist, positioned on the registry key beneath, is ready by Sophos user-space menace detection logic when it detects a malicious driver. On the subsequent boot cycle, SophosEL.sys ensures that this driver will not be loaded.

Buyer choices: Clients can configure remediation and allowed gadgets within the Risk Safety coverage from Sophos Central.

Extra measures: Any Microsoft or Sophos-signed driver is exempt from cleanup/blocking.

What it does: SophosED.sys (Endpoint Protection) is a boot begin driver, began throughout ELAM processing and earlier than many different kernel drivers are loaded, Home windows user-space is initialized, and the system drive is mounted. It has three broad obligations:

1. Offering tamper safety for the Sophos set up and configuration
2. Exposing system exercise occasions to Sophos user-space elements for cover and detection
3. Recording low-level system exercise occasions to the Sophos Occasion Journals for after-the-fact forensics and evaluation

Inputs: Since SophosED.sys begins earlier than the filesystem is out there, its complete configuration is offered by its service key. Observe that each one the beneath inputs are underneath HKLMSYSTEMCurrentControlSetServicesSophos Endpoint Protection.

Filter driver altitudes inputs

SophosED.sys registers with Home windows as a Mini-Filter driver at a number of altitudes (a novel identifier that defines a driver’s place on the ‘stack’ of drivers, with ‘decrease’ drivers being nearer to reveal steel) allotted and permitted by Microsoft.

Tamper Safety inputs

Sophos Tamper Safety is configured by a mix of buyer insurance policies, Sophos characteristic flags, and signed manifests constructed into the agent.

* The configuration password is hashed with PBKDF2-SHA512 and a salt

System Exercise Occasions inputs

The Sophos Central Risk Safety coverage helps a number of configuration choices, which Sophos user-space processes write to the SophosED.sys registry key, in order that they’re out there when the driving force is loaded.

Occasion Journal inputs

Buyer choices: Clients can configure disk limits and handle exclusions in Sophos Central Risk Safety coverage.

Extra measures: If a driver facility is out there (primarily based on a mix of Buyer Coverage plus Sophos flag), then Sophos user-space processes can configure varied parameters at runtime:

• A bitmask of mitigations to use per-process
• What occasions to allow or disable for every course of
• The period of time the driving force ought to watch for a response from user-space (or whether or not it must be an asynchronous notification).

What it does: Sntp.sys (Sophos Community Risk Safety) is a kernel driver that registers for varied Home windows Filtering Platform occasions to intercept and probably modify community move knowledge. Relying on options enabled by Sophos Central Risk Safety and Internet Management insurance policies, completely different filters and callouts are registered.

Inputs: Characteristic configuration is communicated to the driving force from a number of of the next person mode processes:

• SophosNtpService.exe
• SophosNetFilter.exe
• SophosIPS.exe
• SSPService.exe

Person-space processes talk with the driving force through the Home windows Driver Framework, utilizing IOCTLs, Learn, and Write. Communications to and from the driving force are protected, solely accepting connections from licensed and genuine Sophos processes.

Buyer choices: The filter driver intercepts community visitors by browser and non-browser processes primarily based on the insurance policies outlined in Sophos Central. Processing of the intercepted visitors is carried out in user-space by SophosNetFilter.exe and SophosIPS.exe, which can ship modified content material again to the driving force (for instance, to show a block web page for malicious content material).

Extra measures: Clients can add particular person websites to their enable or block listing in Sophos Central.

What it does: Hmpalert.sys enforces Sophos CryptoGuard, which detects and prevents bulk encryption of information by ransomware. It additionally configures what exploit mitigations are enforced as processes are executed.

Inputs: Hmpalert.sys has numerous inputs, together with a number of registry subkeys and IOCTLS.

Buyer choices: Clients can allow/disable exploit mitigations and handle exclusions in Sophos Central Risk Safety coverage.

Extra measures: N/A

What it does: SophosZtnaTap.sys is a Sophos-built OpenVPN TAP driver. If the shopper deploys the Sophos Zero Belief Community Entry (ZTNA) agent, the driving force intercepts DNS lookups for managed functions, and redirects visitors for these functions to the relevant Sophos ZTNA gateways. ZTNA functions and gateways are configured by Sophos Central insurance policies and saved within the registry.

Inputs: Inputs into SophosZtnaTap.sys are through a registry subkey.

Buyer choices: Clients can handle their ZTNA-protected functions and gateways from Sophos Central.

Extra measures: N/A

Sophos CryptoGuard has protected towards bulk encryption on everlasting disks for over a decade. Intercept X model 2024.1.1 launched a brand new characteristic, CryptoGuard ExFAT, which extends this safety to ExFAT partitions (usually discovered on detachable USB drives).

CryptoGuard ExFAT improvement and testing happened in September 2023 by March 2024. This characteristic was guarded by the flag ‘hmpa.cryptoguard-exfat.out there.’

Sophos Engineering ran the software program internally with the flag enabled (our ‘Dogfood launch’) beginning March 22, 2024.

Intercept X model 2024.1.1 was launched to Sophos, then to clients utilizing our gradual software program deployment course of, between Might 21, 2024 by June 6, 2024. At this stage the characteristic was nonetheless dormant for everybody other than Sophos engineers.

The ’hmpa.cryptoguard-exfat.out there’ flag was enabled utilizing our gradual flag enablement course of, between June 10, 2024 by June 26, 2024.

Clients can choose a hard and fast software program model (Endpoint Software program Administration: Fastened-term assist, Lengthy-term assist). This locks the software program and flags till the shopper selects a special software program package deal. Clients who use the ‘Sophos really useful’ possibility obtain new software program periodically. Apart from software program rollouts, in addition they obtain gradual feature-flag enablements for brand spanking new options within the software program, as with a standard software program launch. Sophos has developed this course of to enhance stability and keep away from enabling new occasions globally for all clients.

Kernel drivers are basic to the Intercept X Superior product – and to sturdy Home windows endpoint safety, typically – however we additionally acknowledge that working in kernel-space will not be with out its dangers.

On this article, we’ve walked by the kernel drivers in Intercept X Superior (as of launch 2024.02), what they do, how they’re signed, what their inputs are, the management clients have over their administration, and extra safeguards we’ve put in place – together with gradual, phased rollouts of latest options, and exemptions to reduce the danger of disruption.

Whereas no safeguard can ever get rid of danger altogether, we wished to share the main points of our drivers within the pursuits of transparency, and to clarify in depth how we strategy the advanced drawback of attempting to guard our clients from threats, in as secure a way as potential.