CVE-2026-69303: Push Message Routing Information Disclosure

CVE-2026-69303 Overview

CVE-2026-69303 is an out-of-bounds read vulnerability [CWE-125] in the Push Message Routing Service. An authorized local attacker can read memory outside allocated buffer boundaries to disclose sensitive information. The flaw requires low privileges and no user interaction, but limits impact to the local host. Microsoft documents the issue in its Security Update Guide.

Critical Impact
Local information disclosure through out-of-bounds memory reads in the Push Message Routing Service. Attackers with low privileges can access sensitive process memory without user interaction.

Affected Products

Push Message Routing Service (specific product versions listed in the Microsoft Security Update Guide)
Microsoft Windows components implementing the Push Message Routing Service
Refer to the Microsoft Security Update Guide CVE-2026-69303 for the complete affected build list

Discovery Timeline

2026-09-08 - CVE CVE-2026-69303 published to NVD
2026-09-08 - Last updated in NVD database

Technical Details for CVE-2026-69303

Vulnerability Analysis

The vulnerability is an out-of-bounds read [CWE-125] within the Push Message Routing Service. The service reads memory past the intended buffer boundary when handling specific inputs from a local authenticated user. This condition exposes adjacent memory contents to the attacker.

Exploitation requires local access and low privileges. The attack does not require user interaction and does not affect integrity or availability. Impact is confined to confidentiality, allowing disclosure of process memory that may contain sensitive data such as tokens, keys, or pointers useful for chaining further attacks.

The EPSS score is 0.396%, reflecting a low probability of exploitation in the near term. No public proof-of-concept or in-the-wild exploitation has been reported at publication.

Root Cause

The root cause is missing or insufficient bounds validation on a read operation within the Push Message Routing Service. When the service processes a crafted request or message, it dereferences memory beyond the allocated region. The classification under CWE-125 confirms the read-side boundary violation rather than a write-side corruption issue.

Attack Vector

The attack vector is local, requiring the attacker to authenticate to the target system with low-privilege credentials. Once authenticated, the attacker interacts with the Push Message Routing Service through its exposed interfaces to trigger the out-of-bounds read. The disclosed memory contents can then be extracted and analyzed offline.

No verified exploit code is publicly available. Technical details are described in prose only; see the Microsoft Security Update Guide CVE-2026-69303 for vendor-supplied information.

Detection Methods for CVE-2026-69303

Indicators of Compromise

Unexpected process interactions with the Push Message Routing Service from low-privileged user contexts
Anomalous crash or exception events logged by the service, which may indicate probing attempts
Repeated malformed requests to the service's local IPC endpoints from non-administrative processes

Detection Strategies

Monitor process behavior for local user accounts querying or messaging the Push Message Routing Service outside normal operational patterns
Correlate Windows Error Reporting entries and service exception events with local user sessions
Establish baselines for legitimate consumers of the service and alert on deviations

Monitoring Recommendations

Enable detailed audit logging for local IPC and RPC endpoints exposed by the Push Message Routing Service
Track process creation and command-line telemetry for tools attempting to enumerate or interact with the service
Aggregate endpoint telemetry into a centralized data lake to hunt for repeated low-and-slow probing patterns

How to Mitigate CVE-2026-69303

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update Guide CVE-2026-69303 as soon as it is available for your build
Inventory endpoints running the Push Message Routing Service and prioritize multi-user or shared systems
Restrict interactive local logon rights to reduce the pool of accounts that can trigger the flaw

Patch Information

Microsoft has documented CVE-2026-69303 in its Security Update Guide. Administrators should consult the vendor advisory for the definitive list of affected builds and corresponding update KBs. Deploy the patch through standard Windows Update or your enterprise patch management workflow.

Workarounds

Limit local access to trusted users only, particularly on servers and shared workstations
Enforce least privilege for standard user accounts to reduce the ability to interact with system services
Monitor and alert on abnormal use of the Push Message Routing Service until patches are deployed

bash

# Configuration example
# Verify installed updates on Windows hosts
Get-HotFix | Sort-Object -Property InstalledOn -Descending

# Check the status of the Push Message Routing Service
Get-Service | Where-Object { $_.DisplayName -like '*Push*' }