Following on from our current article on the kernel drivers in Sophos Intercept X, during which we mentioned how they’re examined and what they do, we’re offering additional transparency into the interior workings of Intercept X – this time with a take a look at content material updates which might be both configuration adjustments that lead to adjustments to code execution paths, or are code themselves.
Intercept X makes use of a mixture of real-time Cloud lookups and on-device content material updates. As a result of the menace panorama is continually evolving and shifting, it’s essential that on-device content material updates are delivered steadily (some on-device knowledge adjustments much less steadily, however could require updates at brief discover). Nonetheless, this comes with its personal dangers; if content material updates are corrupt or invalid, this may end up in disruption.
Sophos makes use of a typical mechanism to distribute on-device content material updates, that are loaded into low-privileged Sophos user-space processes (slightly than being loaded into or interpreted by Sophos kernel drivers) from Sophos’s Content material Distribution Community (CDN). Content material updates kind one of many three principal parts of Intercept X, together with software program from the CDN, and coverage and configuration from Sophos Central.
On this article, we’ll discover the varied sorts of content material updates we use, how we confirm and validate them, and the way the ecosystem is architected to keep away from points brought on by corrupt or faulty content material. (As we famous in our earlier article, Intercept X (and all its parts) has additionally been a part of an exterior bug bounty program since December 14, 2017.)
It’s price noting that the main points inside this text are appropriate as of this writing (August 2024) however could change sooner or later as we proceed to replace and develop options.
Sophos delivers new content material updates to prospects in ‘launch teams.’ Every Sophos Central tenant is assigned to a launch group.
The primary launch group is for inner engineering testing; we don’t assign any manufacturing prospects to it. This permits our engineering groups to check new content material updates on manufacturing infrastructure, with out requiring any handbook steps. If testing fails, we abort the discharge with out continuing to any additional launch teams.
If engineering qualification succeeds, we manually promote the discharge to the ‘Sophos inner’ launch group (‘dogfooding’). This contains Sophos staff’ manufacturing gadgets, in addition to staff’ private accounts. Once more, if issues are detected or reported, we abort the discharge and don’t proceed any additional.
All being nicely, we then manually promote the discharge to public launch teams. From this level, the Sophos launch programs robotically publish the brand new content material replace to all the discharge teams over a interval of a number of hours or days by default (see Determine 1 under).
Determine 1: Phases of launch, with verification checks at every section
Sophos AutoUpdate – a part of Intercept X – checks for brand new content material updates each hour, though in apply updates are much less frequent than this (see desk under).
Sophos AutoUpdate downloads every content material replace from the CDN and checks to see if new content material replace packages can be found for the suitable launch group.
Content material updates are time-stamped and signed utilizing SHA-384 and a non-public Sophos certificates chain. Sophos AutoUpdate verifies the updates it downloads. If it detects corrupt or untrusted updates, it discards them and warns each Sophos and the Sophos Central administrator. As well as, to guard towards stale CDN caches or malicious replay assaults, Sophos AutoUpdate rejects any otherwise-valid replace whose signature timestamp is older than the already-downloaded replace.
If a brand new content material replace package deal is on the market, Sophos AutoUpdate downloads and installs it utilizing the related package deal installer. Totally different updates are dealt with by totally different parts of Intercept X.
The next content material updates are a part of the newest Intercept X launch (2042.2).
Desk 1: An summary of the content material updates which might be a part of the newest Intercept X launch (2024.2)
Determine 2: A diagram illustrating which Sophos processes (proven in navy blue) load which content material updates (proven in purple)
DatasetA
DatasetA is loaded by SophosFileScanner.exe, a low-privilege course of with no filesystem entry (apart from its log folder and a brief listing used for scanning massive objects). It hundreds the Sophos Anti-Virus Interface (SAVI).
SophosFileScanner.exe scans content material following scan requests from different Sophos processes. Though it’s referred to as “SophosFileScanner.exe”, the title is considerably historic: it’s the major content material scanner in Intercept X, scanning recordsdata, course of reminiscence, community site visitors, and so forth.
LocalRepData
LocalRepData comprises two status lists:
- Fame by SHA-256
- Fame by signer
When a Home windows executable begins execution, Intercept X appears to be like it up within the LocalRepData by its SHA-256 hash and its signature (assuming it’s validly signed). If the status is offered by LocalRepData, Intercept X ‘tags’ the method with the status (Sophos guidelines deal with high-reputation recordsdata and processes otherwise – for example, exempting them from cleanup).
SSPService.exe makes use of LocalRepData to assign status as processes launch.
SophosFileScanner.exe additionally hundreds LocalRepData, in order that it could possibly assign status to embedded executable streams it discovers in content material apart from executed recordsdata.
Conduct
Conduct guidelines are loaded by SSPService.exe. Guidelines recordsdata comprise signed and encrypted Lua code. SSPService.exe verifies, decrypts and hundreds the foundations right into a sandboxed LuaJIT interpreter with entry solely to Sophos-internal APIs.
Lua is a quick, embedded scripting language. Sophos makes use of Lua for habits guidelines as a result of it gives a versatile method to ship new habits detections with no need a brand new software program launch, however whereas nonetheless sustaining security. The principles are loaded in user-space, so can not trigger a important system failure in the event that they misbehave. As well as, Sophos builds its guidelines engine with out the Lua base libraries – the one entry to the system is by way of Sophos’ inner API, which is hardened towards unintended misuse by the habits guidelines. Sophos collects intensive telemetry about rule runtimes, and constantly tunes and reduces runtime overhead.
Guidelines are reactors: Intercept X gives numerous occasions, and guidelines register handlers for these occasions. Guidelines may also configure numerous aggregation parameters for some high-volume occasions, permitting the sensor to coalesce or discard sure occasions.
Flags
Flags are the means by which Sophos steadily permits new options in Intercept X. Flags are delivered in two methods:
- The Flags Complement comprises a baseline set of flags akin to the out there options within the software program
- The Flags Service is a Sophos Central microservice that permits Sophos Launch Engineers to configure flags throughout a number of tenants
The Flags Complement for a given software program launch comprises a set of characteristic flags and the way the characteristic needs to be enabled:
| Flag Complement Worth | Flag Service Worth | Function is… |
| Off | Ignored | Off |
| Accessible | Off | Off |
| Accessible | On | On |
This mechanism provides Sophos a number of avenues to allow and disable options.
- Sophos can introduce new options with the flag “Accessible” (however not enabled within the Flags Service)
- Sophos can steadily allow new options utilizing the Flags Service to allow flags throughout tenants
- Sophos can disable a problematic characteristic by disabling the flag within the Flags Service
- Sophos can disable a problematic characteristic in a particular software program launch by altering the discharge’s Flags Complement.
CRT
The Competitor Removing Instrument (CRT) comprises a algorithm for eradicating known-incompatible software program in the course of the set up. It’s robotically downloaded by the installer, and is eliminated after set up.
Usually the CRT just isn’t utilized by Intercept X; nevertheless, if a buyer installs a non-protection element like Sophos Machine Encryption, and later opts to deploy Intercept X, the prevailing agent downloads and installs the CRT and runs it previous to set up. As soon as Intercept X is put in, the CRT is robotically eliminated.
Endpoint Self Assist Ruleset
The Endpoint Self Assist (ESH) guidelines are a set of standard expressions for sure log recordsdata. If Sophos engineers have recognized a typical root trigger or misconfiguration, they’ll publish a brand new rule and hyperlink again to the Data Base Article (KBA) describing the issue and the prompt answer(s).
ScheduledQueryPack
The scheduled question pack content material replace comprises a listing of scheduled queries and their execution frequency. The principles are loaded by SophosOsquery.exe; the output is delivered by McsClient.exe for ingestion by the Sophos Central Knowledge Lake.
SophosOsquery.exe has a built-in watchdog that stops ‘runaway’ queries from consuming extreme CPU or reminiscence. Sophos collects telemetry on scheduled question efficiency, and repeatedly optimizes and tunes scheduled queries to keep away from triggering the watchdog.
RemapperRules
The remapper guidelines are loaded by McsAgent.exe and used to ‘remap’ Sophos Central coverage settings into the Endpoint configuration, saved within the Home windows registry below HKLMSOFTWARESophosManagementPolicy.
The coverage is provided from Central as a set of XML paperwork. The principles are additionally a set of XML paperwork that describe the construction of the information saved within the registry and supply XPath queries and some conversion features to extract content material from the coverage XML and generate registry knowledge.
If a rule file is corrupt, or if processing them fails for another cause, not one of the registry values outlined by that file are up to date and any earlier settings are left intact. Processing of different, legitimate, rule recordsdata is equally unaffected.
EPIPS_data
The EPIPS_data content material replace comprises intrusion prevention system (IPS) signatures loaded by SophosIPS.exe. SophosIPS.exe comprises a Sophos-built IPS product; the signatures are IPS signatures revealed by SophosLabs.
SophosIPS.exe runs as a low-privilege course of. When IPS is enabled, the sntp.sys driver sends packets to SophosIPS.exe for filtering; SophosIPS.exe responds to the motive force with instructions to simply accept or reject the packets.
Interacting with community flows packet-by-packet deep within the community stack requires excessive care. The Home windows Filtering Platform (WFP) callouts at L2 are very delicate to the underlying drivers, typically from third-parties, that service the bodily and media entry layers. Due to the excessive danger to system stability, the IPS characteristic screens itself for BSODs or community disruptions which might be probably brought on by third-party driver interactions. If detected, the IPS characteristic robotically disables itself and units the endpoint’s well being standing to purple as an alert to the incompatibility.
NTP_OVERRIDES
One of many potential points when constructing a Home windows Filtering Platform (WFP) kernel driver is that though the platform is designed for a number of drivers to work together with the filtering stack on the similar time, Sophos has recognized sure third-party software program packages that aren’t suitable with the IPS characteristic, which requires the power to intercept and manipulate L2 packets.
The NTP_OVERRIDES content material replace comprises a listing of known-incompatible drivers. If IPS is enabled in coverage however deployed on a tool with an incompatible driver, SophosNtpService.exe disables IPS, overriding the coverage.
That is delivered as a content material replace in order that as new incompatible drivers are found, Sophos can react dynamically to guard different prospects with the identical configuration. As well as, if Sophos or third-parties replace drivers to handle the incompatibility, Sophos can take away the motive force as of a sure model.
RepairKit
Throughout every hourly replace, Sophos AutoUpdate executes a self-repair program (su-repair.exe) to detect and proper any repairable recognized points. The RepairKit was initially constructed to detect and restore file corruption brought on by unclean shutdowns that might corrupt the Sophos set up. Over time, the Sophos engineering crew has used this facility to appropriate many points that traditionally would have required a Sophos assist engagement with the shopper, or probably gone unnoticed till a future software program replace flagged the problem.
RepairKit guidelines are written in Lua and loaded by su-repair.exe. The principles are encrypted and signed. If su-repair.exe fails to load the RepairKit guidelines, it hundreds a baked-in ‘final resort’ ruleset which solely focuses on repairing Sophos AutoUpdate itself.
RepairKit guidelines have broad entry to the machine and run as SYSTEM, since they want the power to appropriate privileged keys and recordsdata.
TELEMSUP
This telemetry content material replace comprises a JSON doc describing how typically and the place to submit telemetry:
{
"additionalHeaders": "x-amz-acl:bucket-owner-full-control",
"port": 0,
"resourceRoot": "prod",
"server": "t1.sophosupd.com",
"verb": "PUT",
"interval": 86400
}
The telemetry content material replace has not modified because it was launched in 2016.
APPFEED, USERAPPFEED
The APPFEED content material updates comprise signed and encrypted Lua snippets for detecting put in purposes and dynamically producing exclusions for them.
If an software is detected for which the APPFEED comprises exclusion guidelines, the foundations dynamically generate machine-specific exclusions primarily based on the put in software. These exclusions are reported again to Sophos Central for informational show to the Sophos Central administrator.
The principles have read-only entry to the registry and filesystem, and usually function by in search of recognized apps within the Add/Take away Packages registry keys. Some purposes, like Microsoft SQL Server, require executing PowerShell script to detect non-compulsory OS parts.
APPFEED and USERAPPFEED are loaded by an occasion of SEDService.exe.
ProductRulesFeed
Product guidelines are loaded by SSPService.exe. They’re in the identical format as Conduct guidelines, with the identical entry and privileges. They’re loaded into the identical LuaJIT interpreter and supply core performance required by the Conduct guidelines.
ML fashions
The ML fashions content material replace comprises a number of machine studying fashions loaded by SophosFileScanner.exe. Not like most content material updates, ML fashions comprise Home windows DLLs that comprise the core ML mannequin logic, in addition to the ‘weights’ – the results of coaching and tuning fashions within the SophosLabs Cloud.
The ML fashions are loaded by SophosFileScanner.exe and are run in the identical low-privilege surroundings. SophosFileScanner.exe helps loading two variations of every mannequin: ‘telemetry’ and ‘dwell.’ Sophos makes use of this functionality to ship candidate ML fashions in telemetry mode. When SophosFileScanner.exe has an ML mannequin in telemetry mode, it selects a pattern of knowledge for telemetry evaluation, and runs it via the telemetry mannequin (along with regular actions). The output from the telemetry mannequin, alongside the information collected by the conventional fashions, gives telemetry to Sophos for evaluation and coaching.
Sophos delivers ML fashions as content material updates so {that a} new ML mannequin can get a number of iterations of telemetry, retraining, and fine-tuning earlier than being promoted to the dwell mannequin.
For the reason that ML mannequin replace comprises executable code, Sophos releases it extra steadily and with extra gates:
- It spends extra time within the early launch teams (engineering testing and Sophos Inner)
- It’s launched over a number of weeks, not hours.
Hmpa_data
The Hmpa_data content material replace comprises a world allowlist of HitmanPro.Alert thumbprints. Each HitmanPro.Alert detection creates a singular thumbprint for the related mitigation and the detection-specific data. For instance, a thumbprint for a StackPivot mitigation would possibly embrace the method and the previous couple of stack frames.
Hmpa_data comprises a compact record of worldwide allowed thumbprints. The HitmanPro.Alert service hmpalertsvc.exe makes use of this database to rapidly and quietly suppress detections, cut back false positives, and keep away from efficiency or stability points.
- The HitmanPro.Alert driver, hmpalert.sys, generates thumbprints and sends them to the service for any driver-based mitigation: CryptoGuard, CiGuard, PrivGuard, and so on.
- The HitmanPro.Alert hook DLL, hmpalert.dll, which is injected into person processes, generates thumbprints for every detection and sends them to the service for reporting.
With the intention to maintain tempo with the ever-evolving menace panorama, and to guard towards rising threats, it’s vitally vital to repeatedly replace safety merchandise with new knowledge. Nonetheless, corrupt or faulty content material updates may cause disruptions, so it’s additionally important that there are mechanisms in place to assist be sure that they’re legitimate, signed, and verified.
On this article, we’ve offered a high-level overview of the content material updates we use in Intercept X – exploring what they’re, how typically they’re delivered, how they’re validated and verified, the particular low-privileged processes they’re loaded into, and the strategies we use to roll them out in a staged and managed method.
As we alluded to in our earlier article on Intercept X kernel drivers, balancing safety and security is dangerous – however we’re dedicated to managing that danger, as transparently as potential.
