EUVD-2026-100316
GHSA-pqx5-wgc4-wx44
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessObtain local low-privileged access
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ExploitTrigger heap overflow in Windows Update Service
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ExecutionCorrupt heap and hijack execution
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ImpactElevate to SYSTEM privileges
Vulnerability Assessment
| Weakness |
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Heap buffer bounds checking
MITRE ATT&CK
1 technique across 1 tactic: Execution The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Exploitation requires the attacker to already hold a local, authenticated low-privileged account on the target (AV:L, PR:L) and to interact with the Windows Update Service component; no user interaction is needed (UI:N). The AC:H metric indicates a meaningful limiting factor - likely a timing/race window or a specific heap layout that must be achieved for reliable corruption - which reduces exploit reliability. There is no network vector and no special non-default configuration implied; the flaw is reachable against default Windows installations but only from an existing local foothold. |
| Impact | This is a locally-exploitable elevation-of-privilege flaw rather than a remotely-reachable one. The provided CVSS 3.1 vector (AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H, base 7.0 HIGH) is internally consistent with the description ('authorized attacker... elevate privileges locally'): AV:L and PR:L mean the attacker must already have a local, low-privileged foothold, and AC:H indicates a non-trivial precondition such as winning a race or grooming a specific heap state. No EPSS score, CISA KEV listing, or public POC was supplied, so there is no public exploit identified at time of analysis and no evidence of active exploitation. The AC:H rating and local-only vector materially lower real-world risk versus a network-reachable EoP; this reads as a patch-in-normal-cycle issue that becomes relevant primarily as a post-compromise escalation primitive, not an internet-facing emergency. Key missing signals to note explicitly: no exploitation-probability (EPSS) data, no KEV status, no SSVC decision values, and no specific affected build numbers were provided - only a single MSRC advisory link. |
| Exploit ScenarioDerived | An attacker who already has low-privileged code execution on a Windows host (e.g., via a standard user account or a compromised low-integrity process) triggers a crafted condition in the Windows Update Service to corrupt heap memory. Because attack complexity is high, success typically requires winning a race or precisely shaping heap allocations, after which the attacker gains SYSTEM-level privileges. No public proof-of-concept was identified in the provided data. |
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Alert meAnalysisAIv1 – Oct 13, 2026
Local privilege escalation in the Microsoft Windows Update Service allows an attacker who already holds a low-privileged, authenticated local account to trigger a heap-based buffer overflow and corrupt memory in a service that runs with high privileges, potentially yielding full control of confidentiality, integrity and availability on the host (CVSS 3.1 base 7.0, AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H). Because the service listens on no network interface for this issue, exploitation requires an existing local foothold rather than remote access, and the High attack-complexity rating indicates a real reliability barrier - most likely a timing window or a specific heap layout that must be won before corruption succeeds. No public exploit code has been identified at time of analysis, KEV status is not indicated, and no EPSS score was supplied, so this should be treated as a post-compromise escalation primitive rather than an opportunistic remote threat.
RemediationAI
Apply the Microsoft security update that resolves CVE-2026-100203 as documented in the vendor advisory (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-100203); no exact fix build or KB number is confirmed in the supplied data, so do not assume a specific patch level and verify the applicable update on the MSRC update guide before closing the finding. If an update is not yet deployable, the practical compensating controls are constrained by the fact that exploitation already requires a local authenticated foothold: prioritise removing that foothold by restricting interactive and secondary logon rights, eliminating shared or service accounts with local access, and enforcing least privilege so few identities can run code on the host, accepting that this reduces rather than removes exposure for legitimate local users. Disabling the Windows Update Service is not a viable mitigation - it breaks the patching pipeline that remediates this and other flaws and creates a larger long-term risk - so it should only be considered in isolated, non-patch-dependent environments, with the side effect of leaving the system unpatched. Because the assessed AC:H reflects a narrow heap-layout or timing requirement, detection should focus on anomalous process activity or unexpected crashes in Windows Update components rather than on network indicators, since no network vector applies.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 16 packages in euvd
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
The defect is a CWE-122 heap-based buffer overflow - a write past the bounds of a heap-allocated buffer, corrupting adjacent heap metadata or objects and enabling controlled memory corruption in the address space of the affected process. The component involved is the Windows Update Service, the privileged Windows component (traditionally the wuauserv service) that brokers update downloads, orchestration and installation and that executes as a high-integrity/system context, which is precisely why a memory-safety bug reachable from a low-privileged local caller converts into elevation of privilege. The supplied CVSS vector (AV:L/AC:H/PR:L/UI:N/S:U) tells us the attack surface is local and caller-authenticated, that no user interaction is needed, and that scope is unchanged (U), so impact is confined to the target host. The AC:H metric is the key analytical signal: heap overflows in service processes typically require heap grooming, allocation-size control, or winning a race against the service's worker threads, all of which reduce repeatability and make reliable exploitation substantially harder than a straightforward stack overwrite. No CPE entries were included in the source data, so the exact affected Windows builds and editions are not enumerated here and must be taken from the Microsoft advisory.
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Severity by source
AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Local-only EoP from an existing low-privileged account (AV:L, PR:L); high complexity reflects the heap-grooming/race precondition, and successful SYSTEM compromise yields full C/I/A impact.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
2DescriptionCVE.org
Heap-based buffer overflow in Windows Update Service allows an authorized attacker to elevate privileges locally.
Executive ViewAI
A high-severity local privilege escalation flaw in the Microsoft Windows Update Service could let an attacker who already has a foothold on a Windows host elevate to full administrative control, compromising the confidentiality, integrity and availability of that system. The practical exposure is limited to environments where an intruder has already obtained a low-privileged local account - it cannot be triggered remotely - but on any such host it becomes a fast path from a minor beachhead to domain-relevant control. Leadership should treat this as a post-compromise escalation risk that raises the value of every existing foothold, particularly on privileged workstations, servers and jump hosts, while no vendor patch is yet available.
No vendor-released patch identified at time of analysis. Interim mitigations: strict least-privilege enforcement so no standard user retains local or RDP access to sensitive hosts; removal of unnecessary and dormant local accounts; hardening of local logon rights on Tier 0/Tier 1 systems; application allowlisting and host hardening to block post-exploitation privilege-escalation tooling; EDR and Windows event log monitoring for suspicious activity in or around the Windows Update Service, including service crashes and privilege-escalation behaviour; and rapid containment playbooks that treat any host compromise as a potential full administrative compromise.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.
A heap overflow occurs when a program writes data beyond the bounds of a buffer allocated in the heap memory region.
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