Vulnerability Summary
| Field | Details |
|---|---|
| CVE ID | CVE-2026-23651 |
| Vulnerability Name | Azure Compute Gallery Regex Validation Privilege Escalation |
| Affected Product | Microsoft Azure Compute Gallery |
| Vendor | Microsoft |
| Severity | High |
| CVSS Score | 7.5 (Estimated) |
| Attack Vector | Authenticated / Local |
| Privileges Required | Low |
| User Interaction | None |
| Scope | Changed |
| Impact | Privilege Escalation, Unauthorized Resource Manipulation |
| Exploitability | Moderate |
| Exploit Availability | No publicly weaponized exploit reported; conceptual exploitation possible |
| CWE | CWE-20 Improper Input Validation |
| Vulnerability Type | Weak Regular Expression Validation |
| Affected Environment | Azure cloud environments using Azure Compute Gallery for VM image management |
Overview
CVE-2026-23651 is a privilege escalation vulnerability identified in Azure Compute Gallery, a Microsoft Azure service used for managing and distributing virtual machine images across cloud environments.
The issue originates from a weak regular expression validation mechanism used during the processing of user-supplied identifiers and metadata associated with virtual machine images. Because the validation pattern does not strictly enforce allowed input formats, specially crafted input values may pass validation checks.
When such malformed input is processed by internal backend components, incorrect assumptions about the validity of the data may be made. Under specific conditions, this behavior may allow a low-privileged authenticated user to manipulate resource operations and escalate privileges within the Azure resource environment.
The vulnerability does not allow anonymous exploitation. However, if access to the Azure Compute Gallery API or management interface is already available, the validation weakness may be abused to perform actions that normally require elevated permissions.
Affected Component
The vulnerability affects the Azure Compute Gallery service, which is responsible for managing and distributing virtual machine images within Azure.
This service supports several critical operations including:
- Image version management
- Image replication across regions
- Image sharing between subscriptions
- VM deployment using predefined images
- Image metadata management
Because the service interacts with deployment automation and infrastructure provisioning pipelines, manipulation of image metadata may affect downstream operations.
Root Cause
The root cause of this vulnerability is attributed to insufficient input validation using a permissive regular expression.
Regular expressions are typically used to validate identifiers such as image names, gallery names, or metadata fields. In this case, the implemented validation pattern was not restrictive enough.
Possible weaknesses include:
- Missing beginning or end anchors in regex patterns
- Allowing characters outside the intended input set
- Incomplete validation of nested fields
- Improper sanitization of metadata parameters
- Lack of canonicalization before validation
As a result, certain malicious input values containing unexpected characters or structures may be accepted by the validation layer.
Once such values reach backend processing modules, unintended behavior may occur. These backend components may interpret the manipulated input differently, which may lead to privilege escalation.
Attack Prerequisites
Successful exploitation typically requires the following conditions:
- The attacker possesses valid authenticated access to Azure
- The attacker has permissions to interact with Azure Compute Gallery resources
- The target environment is running a vulnerable backend implementation
- Input validation protections have not yet been patched
No additional user interaction is required once the crafted request is submitted.
Attack Scenario
An attacker with minimal access to an Azure environment may attempt to exploit the vulnerability using the following approach.
- Access to Azure Compute Gallery is obtained using a valid user account with limited permissions.
- A request is submitted through the Azure API, CLI, or management interface to create or modify an image resource.
- Malicious values are inserted into fields such as:
- image name
- gallery identifier
- image metadata fields
- resource naming parameters
- The malformed input bypasses validation because the regex pattern allows unexpected characters.
- The backend service processes the request and incorrectly interprets the manipulated identifier.
- The attacker may then gain elevated privileges or modify protected resources.
- Unauthorized actions may then be performed within the Azure environment.
In certain situations this could allow:
- modification of existing image definitions
- creation of unauthorized image versions
- manipulation of deployment templates
- escalation to administrative permissions within the gallery scope
Impact
If successfully exploited, the following consequences may occur:
- Privilege escalation within Azure resources
- Unauthorized modification of VM images
- Injection of malicious images into deployment pipelines
- Unauthorized access to image repositories
- Resource manipulation within shared galleries
- Potential supply chain compromise in automated deployments
Because many organizations rely on image galleries for automated infrastructure deployment, compromised images could propagate across multiple virtual machine instances.
MITRE ATT&CK Mapping
| Tactic | Technique | Technique ID |
|---|---|---|
| Initial Access | Valid Accounts | T1078 |
| Privilege Escalation | Exploitation for Privilege Escalation | T1068 |
| Defense Evasion | Exploit Public Facing Application | T1190 |
| Persistence | Account Manipulation | T1098 |
| Impact | Resource Hijacking | T1496 |
Proof of Concept (Educational)
The following example demonstrates how malformed input may be submitted during image creation.
This example is provided for educational and defensive research purposes only.
Example Malicious Request
POST /subscriptions/{subscription-id}/resourceGroups/{group}/providers/Microsoft.Compute/galleries
Example payload:
{
"name": "gallery-test../admin-access",
"location": "eastus",
"properties": {
"description": "test payload",
"identifier": "image$(whoami)"
}
}
Example malicious resource identifier:
imageName=prod-image../../privileged-resource
Example bypass attempt:
imageName=test-image$(id)
Because the validation pattern fails to restrict such characters, these payloads may be accepted by the API.
Indicators of Suspicious Activity
Security teams should watch for the following anomalies:
- Image resource names containing unexpected characters
- Multiple image creation requests from low privilege accounts
- Unexpected modification of gallery image definitions
- Sudden privilege changes related to gallery operations
- Image identifiers containing traversal patterns
- Rapid repeated gallery API calls
Unusual metadata values associated with gallery resources should be considered suspicious.
Detection
Monitoring Azure logs is essential for identifying potential exploitation attempts.
The following log sources are recommended for investigation:
- Azure Activity Logs
- Azure Resource Manager Logs
- Azure Compute Logs
- Azure AD Audit Logs
- Microsoft Defender for Cloud alerts
Detection should focus on unusual image naming patterns and unexpected gallery operations.
Detection Rules
Azure Activity Log Query
AzureActivity
| where OperationNameValue contains "Compute"
| where ResourceProviderValue == "Microsoft.Compute"
| where ActivityStatusValue == "Succeeded"
| where Resource contains ".."
or Resource contains "$("
or Resource contains ";"
Azure Resource Manager Query
AzureDiagnostics
| where Category == "Administrative"
| where OperationName contains "galleries"
| where requestBody_s contains ".."
or requestBody_s contains "$("
or requestBody_s contains "`"
Microsoft Sentinel Query
AzureActivity
| where OperationName contains "Gallery"
| where CallerIpAddress != ""
| where ResourceGroup contains ".."
or Resource contains "$("
or Resource contains ";"
| summarize count() by Caller, ResourceGroup, OperationName
Suspicious Metadata Detection
AzureDiagnostics
| where ResourceProvider == "MICROSOFT.COMPUTE"
| where OperationName contains "image"
| where requestBody_s matches regex @"(\.\.|`|\$\()"
Log Sources
The following log sources provide visibility into exploitation attempts.
| Log Source | Description |
|---|---|
| Azure Activity Logs | Records management operations performed in Azure |
| Azure Resource Manager Logs | Tracks API requests made to Azure services |
| Azure Compute Logs | Provides telemetry related to compute resources |
| Azure AD Audit Logs | Tracks identity and permission changes |
| Microsoft Defender for Cloud | Detects anomalous behavior within Azure infrastructure |
Mitigation
The following defensive actions are recommended:
- Apply the latest Microsoft security updates immediately.
- Restrict access to Azure Compute Gallery management APIs.
- Enforce strict role-based access control policies.
- Monitor resource naming conventions.
- Implement input validation within custom deployment scripts.
- Enable Azure Defender security monitoring.
Regular review of access permissions and audit logs should be conducted.
Patch / Upgrade
Microsoft has addressed this vulnerability by strengthening validation logic within Azure Compute Gallery.
Official patch information is available from the Microsoft Security Response Center.
Official Patch Link:
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-23651
Defensive Recommendations
To reduce risk, organizations should implement the following practices:
- Restrict image management permissions to trusted administrators.
- Monitor gallery operations for unusual patterns.
- Enable continuous cloud security monitoring.
- Perform periodic reviews of deployment pipelines.
- Implement strong input validation for automated provisioning scripts.
Ensuring that only trusted images are used within deployment pipelines will help prevent potential compromise.
