decrypted · 10 september 2026 · vulnerabilities and patching · supply chain · ai and llm security

A wormable DNS flaw headlines Microsoft's biggest Patch Tuesday yet

Microsoft's September Patch Tuesday landed this week as the largest security update in the company's history, closing in on a thousand fixes in one release. Buried in that pile is a Windows DNS Server flaw that deserves more attention than its place in the changelog suggests: an unauthenticated, network-exploitable bug that Trend Micro's Zero Day Initiative is already calling SigRed's spiritual successor. For UK organisations running Windows Server domain controllers, which is most of them, this is the patch to prioritise this week.

What actually broke

CVE-2026-69730 is a use-after-free vulnerability in Windows DNS Server, scoring 9.8 out of 10. An attacker needs no credentials and no user interaction: one crafted network packet to a vulnerable DNS service is enough to run arbitrary code. Microsoft installs DNS Server on every domain controller by default and recommends keeping it there, so the flaw sits on the machine that answers name lookups and issues authentication tickets for the whole network. It is one of twenty vulnerabilities in this release that Microsoft rates as wormable, capable of spreading machine to machine with no human involved, the same property that made SigRed, and before it WannaCry, so damaging.

The same update fixes two vulnerabilities already being exploited: CVE-2026-81963 in the Windows Update Stack and CVE-2026-85880 in the ALPC subsystem, both privilege escalation bugs that hand a local attacker SYSTEM rights. Neither reaches a victim over the internet, but both are exactly what an attacker wants once they have landed on a machine by some other route, which describes most real intrusions.

The Secure by Design lesson

The design decision worth scrutinising is not Microsoft's patching, which was prompt once the flaw surfaced. It is the default that puts a critical, potentially reachable service on the same box that holds the keys to network authentication. Domain controllers were never meant to be reachable from untrusted networks, yet DNS is exactly the kind of service that ends up exposed by accident, through a loosened firewall rule, a misconfigured branch VPN, or a legacy trust relationship nobody remembers granting. The lesson for UK IT teams is not only to patch domain controllers first, though that is this week's job. It is to treat DNS exposure as a question to verify continually, not an assumption to make once, echoing the NCSC's recent advice that organisations should confirm rather than assume their operational technology is off the internet. A wormable flaw on infrastructure nobody thought was reachable is exactly how these incidents start.

Also this week

An AI coding agent's sandbox trusted the wrong header. DeepSeek Harness, an open-source tool for running AI coding agents locally, authenticated its local web interface by checking the client-supplied Host header rather than verifying where a connection actually came from. A single shell command from the agent itself could flip its session into "danger-full-access" mode, disabling the sandbox and every approval prompt with it, and an unauthenticated network attacker could do much the same to seize the agent and read its stored conversations. VulnCheck tracked the flaw as CVE-2026-82533, rated 9.4, and DeepSeek shipped a fix in late August adding proper token-based authentication. It is a reminder that a sandbox is only as trustworthy as the check deciding who may open it, an old design flaw in new agentic clothing.

A developer tool's registry served malware for fourteen hours. Coder, used by engineering teams to run cloud development environments, disclosed that an attacker compromised its Cloudflare account and slipped a rogue server into the pool serving its Terraform module registry. Between 07:35 and 21:45 UTC on 31 August, anyone pulling modules from the registry risked downloading code built to harvest cloud, CI/CD and AI-tooling credentials and send them to a lookalike domain. Coder has patched the registry and published fixed releases, but the incident joins a growing ledger of build-time and registry-level supply chain compromises, and a reminder that when a registry itself lied to you, credential rotation, not just a version bump, is the correct response.

Sources

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