What is the CVSS score of CVE-2026-26164?

CVE-2026-26164 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. EPSS exploitation probability: 0.1%.

Which versions of Microsoft 365 Copilot are affected by CVE-2026-26164?

Microsoft 365 Copilot Business Chat contains an unauthenticated injection vulnerability (CVE-2026-26164, CVSS 7.5) that allows remote attackers to extract sensitive information without credentials.. A patch is available.

How to fix or mitigate CVE-2026-26164?

Within 24 hours: Identify all users and tenants with Microsoft 365 Copilot Business Chat enabled and audit access logs for anomalous activity. Within 7 days: Apply Microsoft's released patch to all affected Copilot instances and verify deployment across the environment. Within 30 days: Conduct a security review of sensitive information potentially accessed during the vulnerability window and implement enhanced monitoring on Copilot Business Chat activity.

Microsoft 365 Copilot CVE-2026-26164

EUVD-2026-28446 HIGH

Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') (CWE-74)

2026-05-07 microsoft

GHSA-qvcj-rgrx-wm72

Information Disclosure Microsoft 365 Copilot S Business Chat

7.5

CVSS 3.1 · NVD

Temporal: 6.5

Severity by source

NVD PRIMARY

7.5 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CIRCL (temporal)

6.5 MEDIUM

cvss

Primary rating from NVD.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Lifecycle Timeline

Analysis Generated

May 07, 2026 - 22:00 vuln.today

CVE Published

May 07, 2026 - 20:58 nvd

HIGH 7.5

DescriptionCVE.org

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

AnalysisAI

Injection vulnerability in Microsoft 365 Copilot's Business Chat enables remote unauthenticated attackers to extract sensitive information through specially crafted inputs. Microsoft has released a patch addressing this CWE-74 injection flaw. With CVSS 7.5 (High), network-accessible attack vector, and no authentication required, this represents a significant exposure for organizations using Copilot Business Chat, though no active exploitation is confirmed at time of analysis.

Technical ContextAI

CWE-74 describes improper neutralization of special elements passed to downstream components - a classic injection vulnerability class. In this context, Microsoft 365 Copilot's Business Chat (cpe:2.3:a:microsoft:microsoft_365_copilot's_business_chat) likely processes user-supplied prompts or queries that are then passed to backend AI/LLM components, data retrieval systems, or integrated Microsoft Graph APIs. The vulnerability suggests that specially crafted input containing control characters, prompt injection sequences, or markup elements is not properly sanitized before being used by downstream processing components. This could allow attackers to manipulate the semantic context of Copilot queries, bypass access controls in integrated data sources, or extract information from contexts outside the attacker's authorized scope. Similar injection classes in AI assistants have enabled extraction of system prompts, retrieval of other users' data, or exfiltration of information from connected enterprise resources.

RemediationAI

Apply the vendor-released patch immediately via Microsoft 365 admin center or through standard Microsoft 365 update channels, as detailed in the official advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-26164. Microsoft typically deploys Copilot fixes through backend service updates that apply automatically to tenant environments, but administrators should verify update status in the Microsoft 365 admin center under Health > Service health. If immediate patching cannot be achieved, consider temporarily disabling Microsoft 365 Copilot Business Chat feature through tenant-level policies until the fix is confirmed deployed. This can be accomplished via Microsoft 365 admin center under Settings > Org settings > Copilot, though this eliminates productivity benefits of the service. Network-level controls are ineffective given the cloud-hosted nature of the service. For high-sensitivity environments, implement data loss prevention (DLP) policies to limit Copilot's access to classified or regulated data sources until patching is verified, accepting reduced functionality as trade-off.