Cyber Resilience

CVE-2026-26133

RCE in Microsoft Outlook ≤ 5.2605.0

RCECommand Injection
Published
16 March 2026
Modified
09 April 2026
Patch / advisory
View advisory
CVSS Score v3.1 7.1
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N
EPSS Score 0.0043 36th percentile
Risk Priority 54 floored blend · peak EPSS

Summary

CVE-2026-26133 is a high-severity Command Injection (CWE-77) vulnerability in Microsoft Outlook. Its CVSS base score is 7.1 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Command and Scripting Interpreter (T1059); ranked at the 36th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

This vulnerability is AI-related — categorised as Enterprise AI Assistants; in the LLM/Generative AI Risks risk domain.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2026-26133 is an AI command injection vulnerability (CWE-77) affecting Microsoft 365 Copilot. Published on 2026-03-16, it carries a CVSS v3.1 base score of 7.1 (AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:L/A:N), indicating a high-severity issue that enables an unauthorized attacker to disclose information over a network.

The vulnerability can be exploited by an unauthorized attacker with network access, requiring low attack complexity and no privileges, though user interaction is necessary. Successful exploitation allows the attacker to achieve high confidentiality impact through information disclosure and low integrity impact, potentially compromising sensitive data within the M365 Copilot environment.

Mitigation details are provided in the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-26133.

OWASP Top 10 for Web (2025)

A05:2025 Injection

EU & UK References

Vulnerability Data

AI command injection in M365 Copilot allows an unauthorized attacker to disclose information over a network.

CWE(s)
CWE-77

AI Security AnalysisAI

AI Category
Enterprise AI Assistants
Risk Domain
LLM/Generative AI Risks
OWASP Top 10 for LLMs 2025
None mapped
AI-specific weaknesses CR
CWE-1427CWE-1426
  • CWE-1427 — Prompt injection (untrusted input to LLM) enabling command/info disclosure in Copilot.
Mapped by Cyber Resilience · not in NVD. Poisoning and extraction cases are routed to MITRE ATLAS instead of a synthetic CWE.
Classification Reason
Matched keywords: ai, m365 copilot

Related Threats

MITRE ATT&CK Enterprise Techniques

T1059 Command and Scripting Interpreter Execution
Adversaries may abuse command and script interpreters to execute commands, scripts, or binaries.
attack.mitre.org →
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 →
T1059.001 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 →
T1059.008 Network Device CLI Execution
Adversaries may abuse scripting or built-in command line interpreters (CLI) on network devices to execute malicious command and payloads.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-42895Same product: Microsoft 365 Copilot
CVE-2026-24299Same product: Microsoft 365 Copilot
CVE-2026-48561Same product: Microsoft 365 Copilot
CVE-2026-42827Same product: Microsoft 365 Copilot
CVE-2026-41090Same product: Microsoft 365 Copilot
CVE-2026-42893Same product: Microsoft Outlook
CVE-2026-33111Same vendor: Microsoft
CVE-2026-42824Same vendor: Microsoft
CVE-2025-53773Same vendor: Microsoft
CVE-2025-59252Same vendor: Microsoft

Affected Assets

microsoft
365 copilot
≤ 2.107.2 · ≤ 16.0.19815.10000
microsoft
edge
≤ 145.3800.99 · ≤ 145.3800.99
microsoft
excel
≤ 2.106.2 · ≤ 16.0.19822.20038
microsoft
loop
≤ 2.106
microsoft
onenote
all versions · ≤ 16.0.19725.20142
microsoft
outlook
all versions · ≤ 5.2605.0 · ≤ 5.2605.0
microsoft
power bi
all versions · ≤ 2.2.260210.21290750
microsoft
powerpoint
≤ 2.106.2 · ≤ 16.0.19822.20038
microsoft
teams
≤ 1.0.0.2026043102 · ≤ 8.3.1
microsoft
word
≤ 2.106.2 · ≤ 16.0.19822.20038

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)
  • V1.2.3
  • V1.2.5
  • V1.2.8
  • V1.2.9

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation can discover command-construction flaws before deployment.

SI-10 Information Input Validation good match

Input validation directly stops construction of commands from untrusted data containing special elements.

SA-8 Security and Privacy Engineering Principles partial match

Secure engineering principles include proper neutralization and safe command construction practices.

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 input validation and neutralization that prevent command injection.

DE.CM-09 partial match
prevents

Runtime monitoring of software and data can detect anomalous command execution resulting from injection.

ID.RA-01 partial match
prevents

Identifying recorded vulnerabilities enables remediation of command-injection flaws before exploitation.

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.8.28 Secure coding mostly match
prevents

Secure coding standards require proper escaping and parameterization of commands, directly eliminating CWE-77.

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

Security testing in development catches command-injection vulnerabilities before release.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle mandates input validation and command construction practices that directly prevent command injection.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly call for controls against injection flaws including command injection.

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

Secure architecture principles reduce the attack surface but do not prescribe the specific neutralization techniques needed.

A.8.31 Separation of development, test and production environments none match
none

Environment separation limits the blast radius of an exploited command injection but does not prevent the flaw itself.

References