January 2026 Patch Tuesday: Exploited DWM Flaw and 112 CVEs Explained

Windows and Microsoft product users are facing renewed urgency after a flurry of security advisories and the January 13, 2026 Patch Tuesday that fixed more than a hundred vulnerabilities — including at least one flaw Microsoft says was actively exploited in the wild — and security agencies and tech outlets are warning users to act now to avoid data theft, privilege escalation and system compromise.

Background / Overview​

Microsoft’s first Patch Tuesday of 2026 (released January 13) addressed a very large batch of problems across Windows and other Microsoft products — more than 110 CVEs in total — and included two to three zero‑day issues of note, one of which Microsoft acknowledged was being actively exploited. Security vendors, national CERTs and patch‑management teams flagged a mix of elevation‑of‑privilege, remote‑code‑execution and information‑disclosure flaws that warrant immediate attention for both home users and enterprise administrators. At the same time, several national CERT advisories and widely read outlets summarized and amplified Microsoft’s guidance, urging users to install the January updates, follow mitigations where patches are not yet available, and review device configurations such as Virtualization‑Based Security (VBS) and Secure Boot certificate settings — because some issues either affect VBS or are tied to expiring Secure Boot certificates that could affect device boot behavior if not addressed. This article summarizes the technical facts, verifies the most important claims from multiple independent sources, explains what to do right now, and offers a critical look at the trade‑offs IT teams may face when applying the fixes.

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What was fixed and why it matters​

The scale: hundreds of CVEs, several high‑impact flaws​

• Microsoft’s January 13, 2026 security update bundle addressed around 112–114 CVEs depending on how trackers tally duplicates and third‑party driver removals. Several respected security firms and researchers published independent tallies that converge on this scale.
• The update set included multiple high‑severity issues: one information‑disclosure zero‑day in Desktop Window Manager (DWM) that Microsoft says has been exploited in the wild, and several elevation‑of‑privilege issues (notably in LSASS and other core services) that, if chained with other bugs or poor privilege separation, could lead to full system compromise.

Why it matters: even seemingly modest information‑disclosure bugs can be the pivot point for larger attacks. The DWM bug (CVE‑2026‑20805) allowed local actors to leak memory addresses and undermine address‑space randomization — a useful primitive for attackers looking to escalate privileges or execute code reliably. Security vendors flagged that this specific issue had been observed in exploitation attempts.

Secure Boot certificate updates and expiry risk​

Microsoft’s cumulative update notes explicitly warn administrators about Secure Boot certificate expiration that begins to affect devices in a phased way starting June 2026 unless certificates are updated. Microsoft added targeted certificate updates and a phased deployment plan to reduce boot‑time disruption but told admins to review guidance and prepare. This is not a vulnerability in the usual sense, but an upcoming certificate lifecycle event that can prevent devices from successfully validating new boot components if not handled correctly.

Known compatibility and functional regressions​

Patching a complex, highly distributed platform inevitably produces side effects. The January cumulative update (KB5074109 for many Windows 11 builds) includes functional changes that some users reported affecting desktop.ini parsing and which removed several legacy modem drivers — actions that may be acceptable for most but could break niche hardware or workflows. That means administrators must balance patch urgency with testing, particularly on specialized or legacy systems.

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Independent verification — cross‑checking the most important claims​

To avoid relying on a single news headline, the largest, load‑bearing claims were cross‑checked against multiple independent sources:

• The volume and classification of the January 2026 Patch Tuesday (≈112 CVEs, mix of Critical and Important) are confirmed by vendor trackers and researchers (CrowdStrike, Tenable, Computer Weekly), which independently reported comparable totals and noted the same actively exploited DWM zero‑day.
• Microsoft’s own support documentation for the January cumulative update (KB5074109) confirms the Secure Boot certificate work, driver removals, and the inclusion of numerous security fixes — matching what the security community reported. This is the canonical vendor source for update logistics and known issues.
• Independent reporting from multiple outlets (CyberScoop, Lansweeper analysis, Security Affairs) corroborates the presence of actively exploited CVEs (DWM information disclosure) and emphasizes the risk vectors (local privilege escalation, RCE via LSASS, document parsing bugs) that security teams must prioritize.
• National CERT advisories and aggregator summaries (for example, advisories and thread summaries circulated in technical communities) echo the practical mitigations: update systems, disable unnecessary features, audit privileges and backups, and apply compensating controls where immediate patching is infeasible.

If a specific numerical claim (for example, “450 million devices affected” or “900 million Windows 10 users”) is cited in an article or headline, treat it as an estimate unless vendor telemetry or market research pins it down exactly. Several forum and social‑media summaries repeat large user counts; those are useful context but not precise operational metrics.

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Immediate actions for every Windows user (home and business)​

The steps below are ordered by impact and practicality. They are concise and actionable.

• Update now: Check Windows Update and install the January 2026 cumulative updates (for many Windows 11 builds that is KB5074109). Reboot after installation. If you manage multiple machines, stage the rollout but prioritize internet‑facing systems and machines used to process untrusted documents.
• Update your antivirus/EDR and run full scans: make sure signatures and detection engines are current and scan endpoints after patching.
• Disable automatic preview/thumbnailing in mail clients and File Explorer where possible — many attacks exploit document parsing or thumbnail generation services. Temporarily disable server‑side document previewing for high‑risk ingestion points.
• Reduce privileges: Ensure users run with least privilege (don’t use an admin account for everyday work), and review local admin assignments. This reduces the blast radius if a low‑privileged flaw is exploited.
• Confirm Secure Boot certificate guidance: For organizations, follow Microsoft’s Secure Boot certificate update guidance to avoid future boot problems. Schedule certificate updates as Microsoft recommends and validate device behavior in a test pool.
• If you cannot patch immediately: apply compensating controls — block or restrict access to untrusted networks, harden remote access (MFA, conditional access), and increase logging for authentication and process anomalies.

Short checklist (copy/paste)

• Install Windows updates and reboot.
• Update AV/EDR engines and run full scans.
• Disable document preview/thumbnailing where practical.
• Enforce least privilege and MFA.
• Review Secure Boot certificate plan (admins).
• Test updates on a representative device pool before broad rollout.

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What IT teams should prioritize and why​

Prioritization framework​

• High priority: systems exposed to the internet, endpoints processing untrusted documents (mail servers, file servers), domain controllers, and systems that host privileged accounts. These are the most valuable targets for attackers and the easiest paths to widespread compromise.
• Medium priority: general purpose desktops and laptops used for everyday productivity. These should be updated quickly but can be staged if necessary to reduce user disruption.
• Low priority (but not to be ignored): isolated lab systems, appliances with vendor‑managed firmware where updates require vendor coordination.

Testing vs. urgency trade‑off​

Patching always carries risk: the January update removed legacy drivers and introduced behavior changes for some Explorer features, and administrators reported regressions in certain niche scenarios. For enterprise environments:

• Test updates in a representative staging group first — unless you are protecting an internet‑facing service under active exploitation, in which case accelerate deployment for that service.
• Use phased deployment: pilot → broad rollout with monitoring → full deployment. Automate rollback plans and keep change windows short but frequent.

Logging and detection​

After applying patches, increase monitoring for:

• Unusual LSASS crash events or authentication anomalies.
• Unexpected elevation or persistence attempts.
• New or unusual memory‑scraping behavior (indicators associated with DWM/ASLR bypass attempts).

EDR telemetry and network‑based detection signatures from major vendors were updated to detect exploitation patterns associated with this Patch Tuesday; enable those rules and confirm detection efficacy.

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Critical analysis: strengths, shortcomings and residual risks​

Notable strengths in the response​

• Microsoft’s January rollout was large and comprehensive, addressing a broad range of components and providing mitigations for both actively exploited issues and public disclosures — a necessary, coordinated effort for a complex ecosystem. Commentary from multiple security vendors confirms the scale and the priority levels applied.
• Microsoft also included operational guidance around Secure Boot certificate updates and phased certificate distribution for safer rollout on diverse hardware — a pragmatic step that acknowledges the risks of certificate churn across billions of devices.

Weaknesses and operational friction​

• The high volume of fixes in a single month creates operational pressure on IT teams: testing every interaction and legacy integration is time consuming. Organizations with many legacy peripherals or specialized drivers may face functional regressions (for example, modem driver removal) that require vendor coordination.
• Public advisories and news headlines sometimes compress nuance into alarmist language. While “actively exploited” is factually correct for some CVEs, the real exploitability varies by configuration, required access level and whether an attacker can chain multiple issues. Blanket panic is counterproductive; measured, prioritized responses are more effective.

Residual risk: patching is necessary but not sufficient​

Patching closes known holes, but attackers regularly adapt. The DWM info‑leak demonstrates how a modest local bug can be exploited as part of a chain. Real resilience demands layered controls: least privilege, threat detection, reliable backups, and strong identity protection (MFA, conditional access). National advisories stress that patching plus hardening and monitoring is the complete playbook.

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Practical mitigations for specific scenarios​

Home users​

• Keep Windows Update enabled and install the January patches. Reboot when requested.
• Enable Microsoft Defender or a reputable antivirus, keep it updated, and run a manual scan after patching.
• Use a standard (non‑admin) account for daily activities.
• Enable MFA (two‑step verification) for key accounts (email, cloud storage, bank logins).

Small business / SMB​

• Apply updates to servers and internet‑facing endpoints first.
• Disable automatic previewing in mail systems or file shares.
• If you rely on legacy hardware (modems, custom drivers), inventory those devices and test the update on a pilot group before broad deployment. Factor in plans if driver removal affects operations.

Enterprise / Managed environments​

• Prioritize domain controllers, mail servers and systems that ingest external documents for immediate patching.
• Review and implement Microsoft’s Secure Boot certificate recommendations for your hardware fleet.
• Ensure EDR coverage and that detection rules for the January flaws are enabled and tested.
• Update patch‑management policy to account for high‑volume months: an accelerated pilot phase plus emergency patch windows is prudent.

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What to watch for next (threat outlook and practical flags)​

• Follow vendor advisories for follow‑up patches and Known Issue Rollbacks (KIR). Microsoft has already indicated it may provide KIRs for some regressions; keep an eye on the Windows release health dashboard.
• Watch for CVEs that make the CISA KEV (Known Exploited Vulnerabilities) catalog; those are the CVEs agencies expect organizations to patch urgently. Multi‑source trackers and CISA entries will accelerate prioritization.
• Expect additional vendor signatures and detection updates from AV/EDR providers. Validate that those updates landed and confirm detection coverage for the DWM info‑leak and any LSASS exploitation heuristics.

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Final assessment — balancing speed and caution​

The January 2026 Microsoft updates fixed a high volume of important and exploitable flaws; the practical reality is that delaying patching indefinitely is riskier than a fast, well‑tested rollout. At the same time, organizations must recognize the operational impact of sweeping updates and test where necessary.

• For most users: install the updates now and reboot, update security software, and apply the short checklist above. This is the fastest way to reduce risk.
• For administrators: pilot and stage updates, but prioritize internet‑facing and document‑handling systems. Coordinate with vendors for hardware or driver dependencies and follow Microsoft’s Secure Boot certificate guidance to avoid future boot disruptions.

Be skeptical of sensational numbers in headlines: treat large user counts as contextual estimates and base operational decisions on asset inventories, vendor advisories and observable telemetry.

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Takeaway checklist — what to do in the next 24–72 hours​

• Check Windows Update and install available cumulative updates (January 13, 2026 updates such as KB5074109 where applicable). Reboot.
• Update and run AV/EDR scans; confirm detection rules are enabled.
• Prioritize patching for internet‑facing servers, document‑ingesting systems and domain controllers.
• Disable file and mail preview/thumbnailing temporarily where feasible.
• Implement least privilege and confirm MFA on critical accounts.
• For admins: review Microsoft’s Secure Boot certificate guidance and plan certificate updates as recommended. Test on a pilot fleet first.

Acting now will reduce the chance of being a reactive victim; combining prompt patching with layered defenses, monitoring and least‑privilege practices is the most defensible posture in the face of ongoing active exploitation campaigns.

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Emergency resources and how to escalate

• If you detect signs of compromise (unexpected privilege changes, unknown persistence, credential theft indicators), isolate the affected system(s), preserve logs, and escalate to your incident response process or vendor‑backed support. National CERT advisories and vendor security pages include incident response guidance and may list hotlines or contact points.

Stay safe and prioritize verified vendor guidance; the combination of fast patching, privilege hardening, secure boot planning, and vigilant monitoring is the practical route out of this high‑risk period.

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Source: digit.in https://www.digit.in/news/general/b...sers-are-at-risk-heres-how-to-stay-safe.html]