CVE-2026-25592 — CRITICAL (CVSS 9.9) AI Security Vulnerability

Q: Is CVE-2026-25592 actively exploited?

No confirmed active exploitation of CVE-2026-25592 has been reported, but organizations should still patch proactively.

Q: How to fix CVE-2026-25592?

1) PATCH: Upgrade Microsoft.SemanticKernel.Core to 1.71.0+ (NuGet) and semantic-kernel to 1.39.3+ (pip) immediately — no exceptions for production systems. 2) WORKAROUND: If patching is delayed, implement a Function Invocation Filter that validates localFilePath against an explicit allowlist before any DownloadFileAsync or UploadFileAsync invocation — this is the vendor-documented compensating control. 3) DETECT: Alert on file writes outside designated agent working directories; monitor for unexpected modifications to /etc/, ~/.ssh/, cron directories, or application config paths from the Semantic Kernel process user. 4) AUDIT: Enumerate all usages of SessionsPythonPlugin in your codebase and CI/CD pipelines; verify dependency versions across all environments. 5) HARDEN: Run Semantic Kernel processes under a least-privilege OS user and within a restricted filesystem namespace — read-only container mounts where possible, seccomp profiles restricting filesystem syscalls.

Q: What systems are affected by CVE-2026-25592?

This vulnerability affects the following AI/ML architecture patterns: agent frameworks, plugin systems, code interpretation sandboxes, AI copilot backends, multi-agent orchestration systems.

Q: What is the CVSS score for CVE-2026-25592?

CVE-2026-25592 has a CVSS v3.1 base score of 9.9 (CRITICAL). The EPSS exploitation probability is 0.07%.

CISO Take

Patch now if you're running Semantic Kernel agents with SessionsPythonPlugin — this is a CVSS 9.9 arbitrary file write reachable by any authenticated user over the network with zero user interaction. The scope change (S:C) in the CVSS vector means successful exploitation can break container isolation, turning a compromised plugin into full host access. If immediate patching to 1.71.0 (.NET) / 1.39.3 (Python) is not possible, implement a Function Invocation Filter to allowlist valid file paths as the vendor-recommended workaround.

Risk Assessment

Critical risk for organizations deploying Semantic Kernel-based AI agents. Network-accessible, low privilege required, no user interaction, scope change — this is close to a worst-case CVSS profile. EPSS (0.058%) indicates no active exploitation observed yet, but path traversal primitives in file I/O plugins are trivial to weaponize once the target API is identified. Risk is amplified in multi-tenant SaaS products built on Semantic Kernel where untrusted users have agent access.

Affected Systems

Package	Ecosystem	Vulnerable Range	Patched
semantic-kernel	pip	< 1.39.3	`1.39.3`
27.8K 17 dependents Pushed 8d ago 100% patched ~7d to patch Full package profile →
Microsoft.SemanticKernel.Core	nuget	< 1.71.0	`1.71.0`

Severity & Risk

CVSS 3.1

9.9 / 10

EPSS

0.1%

chance of exploitation in 30 days

Higher than 21% of all CVEs

Source: EPSS v3 — FIRST.org

Exploitation Status

No known exploitation

Sophistication

Trivial

Attack Surface

AV Network

AC Low

PR Low

UI None

S Changed

C High

I High

A High

Recommended Action

1 step

1) PATCH: Upgrade Microsoft.SemanticKernel.Core to 1.71.0+ (NuGet) and semantic-kernel to 1.39.3+ (pip) immediately — no exceptions for production systems. 2) WORKAROUND: If patching is delayed, implement a Function Invocation Filter that validates localFilePath against an explicit allowlist before any DownloadFileAsync or UploadFileAsync invocation — this is the vendor-documented compensating control. 3) DETECT: Alert on file writes outside designated agent working directories; monitor for unexpected modifications to /etc/, ~/.ssh/, cron directories, or application config paths from the Semantic Kernel process user. 4) AUDIT: Enumerate all usages of SessionsPythonPlugin in your codebase and CI/CD pipelines; verify dependency versions across all environments. 5) HARDEN: Run Semantic Kernel processes under a least-privilege OS user and within a restricted filesystem namespace — read-only container mounts where possible, seccomp profiles restricting filesystem syscalls.

CISA SSVC Assessment

Decision Track

Exploitation none

Automatable No

Technical Impact total

Source: CISA Vulnrichment (SSVC v2.0). Decision based on the CISA Coordinator decision tree.

Classification

Code Execution Supply Chain Data Extraction Framework Agent Plugin AML.T0049 - Exploit Public-Facing Application AML.T0051.001 - Indirect AML.T0053 - AI Agent Tool Invocation AML.T0086 - Exfiltration via AI Agent Tool Invocation AML.T0101 - Data Destruction via AI Agent Tool Invocation AML.T0105 - Escape to Host

Compliance Impact

This CVE is relevant to:

EU AI Act

Art. 15 - Accuracy, Robustness and Cybersecurity

ISO 42001

8.5 - AI System Security A.6.1.2 - AI System Security Controls

NIST AI RMF

GOVERN-1.7 - AI Risk Management — Third-Party Components MANAGE-2.2 - Risk Treatment for AI Systems

OWASP LLM Top 10

LLM06 - Excessive Agency LLM07 - Insecure Plugin Design LLM08 - Excessive Agency

Frequently Asked Questions

What is CVE-2026-25592?

Patch now if you're running Semantic Kernel agents with SessionsPythonPlugin — this is a CVSS 9.9 arbitrary file write reachable by any authenticated user over the network with zero user interaction. The scope change (S:C) in the CVSS vector means successful exploitation can break container isolation, turning a compromised plugin into full host access. If immediate patching to 1.71.0 (.NET) / 1.39.3 (Python) is not possible, implement a Function Invocation Filter to allowlist valid file paths as the vendor-recommended workaround.

Is CVE-2026-25592 actively exploited?

No confirmed active exploitation of CVE-2026-25592 has been reported, but organizations should still patch proactively.

How to fix CVE-2026-25592?

1) PATCH: Upgrade Microsoft.SemanticKernel.Core to 1.71.0+ (NuGet) and semantic-kernel to 1.39.3+ (pip) immediately — no exceptions for production systems. 2) WORKAROUND: If patching is delayed, implement a Function Invocation Filter that validates localFilePath against an explicit allowlist before any DownloadFileAsync or UploadFileAsync invocation — this is the vendor-documented compensating control. 3) DETECT: Alert on file writes outside designated agent working directories; monitor for unexpected modifications to /etc/, ~/.ssh/, cron directories, or application config paths from the Semantic Kernel process user. 4) AUDIT: Enumerate all usages of SessionsPythonPlugin in your codebase and CI/CD pipelines; verify dependency versions across all environments. 5) HARDEN: Run Semantic Kernel processes under a least-privilege OS user and within a restricted filesystem namespace — read-only container mounts where possible, seccomp profiles restricting filesystem syscalls.

What systems are affected by CVE-2026-25592?

This vulnerability affects the following AI/ML architecture patterns: agent frameworks, plugin systems, code interpretation sandboxes, AI copilot backends, multi-agent orchestration systems.

What is the CVSS score for CVE-2026-25592?

CVE-2026-25592 has a CVSS v3.1 base score of 9.9 (CRITICAL). The EPSS exploitation probability is 0.07%.

Technical Details

NVD Description

Semantic Kernel is an SDK used to build, orchestrate, and deploy AI agents and multi-agent systems. Prior to 1.71.0, an Arbitrary File Write vulnerability has been identified in Microsoft's Semantic Kernel .NET SDK, specifically within the SessionsPythonPlugin. The problem has been fixed in Microsoft.SemanticKernel.Core version 1.71.0. As a mitigation, users can create a Function Invocation Filter which checks the arguments being passed to any calls to DownloadFileAsync  or UploadFileAsync and ensures the provided localFilePath is allow listed.

Exploitation Scenario

An adversary with low-privilege access to a Semantic Kernel-backed AI coding assistant — a trial user, a compromised internal account, or an attacker who has obtained a valid API token — sends a crafted agent invocation calling DownloadFileAsync with localFilePath set to '../../.ssh/authorized_keys' and attacker-controlled content as the file payload. The unpatched SessionsPythonPlugin writes the attacker's SSH public key to the host's authorized_keys file, granting persistent SSH access to the underlying infrastructure. In a cloud-hosted multi-tenant scenario, this single request escalates to full control of the agent execution environment and potential lateral movement to other tenant workloads. No UI interaction from a victim is required at any stage.