Cyber Resilience

CVE-2026-26129

Microsoft 365 Copilot Chat

Published
07 May 2026
Modified
17 June 2026
Patch / advisory
View advisory
CVSS Score v3.1 7.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
EPSS Score 0.011 64th percentile
Risk Priority 60 floored blend · peak EPSS

Summary

CVE-2026-26129 is a high-severity Improper Neutralization of Special Elements (CWE-138) vulnerability in Microsoft 365 Copilot Chat. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 36% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.

This vulnerability is AI-related — categorised as Enterprise AI Assistants; in the Privacy and Disclosure risk domain.

The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) and SA-8 (Security and Privacy Engineering Principles) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

Improper neutralization of special elements used in a command ('command injection') in M365 Copilot allows an unauthorized attacker to disclose information over a network.

CWE(s)
CWE-138

AI Security AnalysisAI

AI Category
Enterprise AI Assistants
Risk Domain
Privacy and Disclosure
OWASP Top 10 for LLMs 2025
None mapped
Classification Reason
Matched keywords: m365 copilot

Related Threats

MITRE ATT&CK Enterprise Techniques

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1059 Command and Scripting Interpreter Execution
Adversaries may abuse command and script interpreters to execute commands, scripts, or binaries.
attack.mitre.org →
T1059.001 PowerShell Execution
Adversaries may abuse PowerShell commands and scripts for execution.
attack.mitre.org →
T1059.003 Windows Command Shell Execution
Adversaries may abuse the Windows command shell for execution.
attack.mitre.org →
T1059.004 Unix Shell Execution
Adversaries may abuse Unix shell commands and scripts for execution.
attack.mitre.org →
T1505 Server Software Component Persistence
Adversaries may abuse legitimate extensible development features of servers to establish persistent access to systems.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-38133Same vendor: Microsoft
CVE-2026-32178Same vendor: Microsoft
CVE-2024-38206Same vendor: Microsoft
CVE-2024-49038Same vendor: Microsoft
CVE-2024-43610Same vendor: Microsoft
CVE-2025-48939Shared CWE-138
CVE-2023-42117Shared CWE-138
CVE-2026-20009Shared CWE-138
CVE-2024-38228Same vendor: Microsoft
CVE-2023-21778Same vendor: Microsoft

Affected Assets

microsoft
365 copilot chat
all versions

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.3.12

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match

Input validation enforces neutralization or rejection of special syntactic elements before they reach a downstream interpreter.

SA-8 Security and Privacy Engineering Principles partial match

Security engineering principles include requirements for safe input handling and neutralization of control characters.

SI-15 Information Output Filtering partial match

Output filtering can neutralize special elements before they are interpreted by a receiving component.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require proper neutralization of inputs to prevent injection flaws.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect instances of CWE-138 but does not itself implement the neutralization controls.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle mandates input validation and sanitization that directly prevents improper neutralization of special elements.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly call for controls against injection and malformed input that cause CWE-138.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure system architecture principles reduce attack surface but do not prescribe the specific neutralization techniques needed for CWE-138.

A.8.28 Secure coding partial match
prevents

Secure coding standards require proper escaping and neutralization of special elements, directly eliminating CWE-138.

References