Microsoft Teams EUVD-2026-54316

Based on the CVSS vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N, no special conditions are required - this is remote unauthenticated exploitation over the network against Microsoft Teams without victim interaction. The attack vector is network-accessible, and no non-default configuration, specific feature flag, or elevated privilege is described as a prerequisite. Exploitation is bounded by the following limiting factors: impact is restricted to integrity (I:H) - specifically spoofing and identity impersonation - with no confidentiality breach (C:N) or service disruption (A:N) confirmed. The scope is unchanged (S:U), meaning the exploit does not pivot into adjacent systems beyond Teams itself. The practical reach of spoofing depends on what platform features and integrations trust Teams identity claims downstream.

The CVSS 7.5 (High) score is driven by an exceptionally permissive vector: AV:N (network-reachable), AC:L (no special conditions), PR:N (no authentication), UI:N (no victim interaction), resulting in I:H (high integrity impact). This profile represents a realistic and accessible attack - any network-adjacent unauthenticated attacker can attempt exploitation without needing to satisfy unusual prerequisites. EPSS data was not provided, so probabilistic exploitation likelihood cannot be quantified from this input. KEV status is absent and no POC has been identified, meaning active exploitation is not confirmed. Despite the high CVSS, the bounded impact - C:N, A:N - limits damage to spoofing and impersonation rather than data exfiltration or service disruption. In an enterprise communication platform like Teams, however, identity spoofing carries outsized business risk: impersonating a trusted colleague or executive can enable phishing, approval fraud, or lateral trust abuse. The authentication bypass tag heightens concern because successful exploitation may bypass conditional-access or zero-trust controls relying on Teams-layer identity assertions.

An unauthenticated attacker crafts a JWT with forged identity claims - for example, asserting they are a specific user or service account - and submits it to a Microsoft Teams API endpoint or authentication flow. Because Teams fails to properly verify the cryptographic signature on the token, it accepts the forged claims and processes the request as if it originated from the impersonated identity. No public proof-of-concept has been identified at time of analysis, but the low attack complexity (AC:L) suggests the technique would be straightforward to operationalize once the specific vulnerable endpoint and token format are identified.