CVE-2026-25592 – Arbitrary File Write Leading to Code Execution

Product: Microsoft Semantic Kernel (.NET)
Component: SessionsPythonPlugin
CVE ID: CVE-2026-25592
CVSS v3.x Score: 9.9
Severity: Critical
Vulnerability Type: Arbitrary File Write → Potential Remote Code Execution
Attack Vector: Network
Privileges Required: Low
User Interaction: None
Exploitability: High
Exploit Availability: No publicly weaponized exploit observed; educational proof-of-concept scenarios are feasible
Official Patch / Upgrade:
👉 https://github.com/microsoft/semantic-kernel/security/advisories/GHSA-2ww3-72rp-wpp4

Vulnerability Overview

An arbitrary file write vulnerability was identified in Microsoft Semantic Kernel (.NET), specifically within the SessionsPythonPlugin. Due to insufficient validation and restriction of file path parameters, files could be written to attacker-controlled or unintended locations on the host file system.

When abused in real-world deployments, this flaw could allow an attacker to place or overwrite files outside the intended working directory. Depending on the execution context and file permissions of the running service, this behavior could be escalated into full remote code execution, persistent compromise, or application takeover.

The vulnerability primarily affects applications that expose Semantic Kernel agent or plugin functionality where input parameters—directly or indirectly—can be influenced by external users, other services, or untrusted model outputs.

Root Cause Analysis

The issue was caused by improper handling of file system paths supplied to file-related plugin methods such as upload or download operations. Path canonicalization and boundary enforcement were not consistently applied before writing files to disk.

As a result:

• Absolute paths could be accepted.
• Relative traversal sequences (../) could be used.
• Writes could escape intended sandbox or working directories.

This behavior constitutes a classic path traversal condition (CWE-22) combined with unsafe file write operations.

Impact

If successfully exploited, the following impacts could occur:

• Unauthorized creation or overwrite of files anywhere the service account has write access.
• Placement of executable binaries, scripts, or DLLs on the host.
• Modification of application configuration files.
• Establishment of persistence through startup scripts or scheduled tasks.
• Indirect or direct execution of attacker-controlled code.

The actual impact depends on operating system, runtime privileges, deployment model (containerized vs host), and downstream services that may execute or load written files.

Attack Scenarios

Typical abuse paths include:

• Writing a malicious script into a directory later executed by the application or OS.
• Dropping a payload into a web-accessible directory, enabling remote command execution via HTTP.
• Overwriting existing trusted files to alter application behavior.
• Leveraging writable plugin or extension directories to inject malicious logic.

These scenarios are realistic in environments where Semantic Kernel is used to orchestrate agent workflows, especially when combined with permissive file system access.

Proof of Concept Status (Educational)

No publicly distributed exploit tool or weaponized PoC has been observed. However, from an educational and defensive research standpoint, exploitation is conceptually straightforward:

• A crafted request or agent invocation supplies a manipulated file path.
• The application writes attacker-controlled content to an arbitrary location.
• The written file is later executed or loaded by the system or application.

Detection and Monitoring

Recommended Log Sources

• Application logs generated by the Semantic Kernel host application
• API gateway or reverse proxy logs (if agent endpoints are exposed)
• Host-based file integrity monitoring logs
• Endpoint Detection & Response (EDR) telemetry
• OS audit logs (Windows Security, Linux auditd)

Detection Indicators

• File write operations originating from the Semantic Kernel process.
• File paths containing traversal patterns or absolute paths.
• Creation of executable or script files by non-administrative service accounts.
• Unexpected file writes followed closely by process execution.
• Repeated failed or abnormal plugin invocation attempts.

Detection Queries

Windows (Security Event Log – File Creation)

EventID=4663 AND ObjectType="File" 
AND ProcessName CONTAINS "SemanticKernel"
AND (ObjectName CONTAINS ".." OR ObjectName CONTAINS "System32")

Linux (auditd)

type=PATH AND exe CONTAINS "semantic-kernel"
AND (name CONTAINS "../" OR name STARTS_WITH "/etc/")

Application Logs

FunctionName IN ("DownloadFileAsync","UploadFileAsync")
AND (FilePath CONTAINS ".." OR FilePath STARTS_WITH "/" OR FilePath MATCHES "^[A-Z]:\\")

EDR Behavioral Query

Process = SemanticKernelService
THEN FileWrite
FOLLOWED BY ProcessStart
WITHIN 5 minutes

Mitigation and Remediation

Immediate Actions

• Upgrade all affected Semantic Kernel packages to the fixed version as provided in the official advisory.
• Redeploy applications after patching to ensure the vulnerable code paths are removed.

Compensating Controls

If immediate patching is not feasible:

• Enforce strict allow-listing of file paths before any write operation.
• Reject absolute paths and traversal sequences.
• Restrict the runtime service account to minimal file system permissions.
• Isolate working directories and prevent execution from writable locations.

Post-Patch Validation

After upgrading:

• Verify that file write operations fail when paths escape allowed directories.
• Review historical logs for suspicious file creation events.
• Conduct a targeted file system scan for unexpected artifacts.
• Revalidate CI/CD dependency checks to prevent regression.

MITRE Classification

• CWE: CWE-22 – Improper Limitation of a Pathname to a Restricted Directory
• ATT&CK Tactics:
  • Execution
  • Persistence
  • Privilege Escalation (environment dependent)

Final Takeaway

CVE-2026-25592 represents a high-impact vulnerability that bridges application-level input handling with underlying operating system risk. While exploitation requires some level of access or influence over agent inputs, real-world Semantic Kernel deployments commonly meet this condition.

Prompt patching, restrictive file system permissions, and strong runtime monitoring are critical to reducing risk. Detection engineering should focus on abnormal file write behavior originating from Semantic Kernel processes, especially when followed by execution events.