What is the CVSS score of EUVD-2026-54316?

EUVD-2026-54316 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:N/I:H/A:N. EPSS exploitation probability: 0.3%.

Which versions of Microsoft Teams are affected by EUVD-2026-54316?

A critical identity verification vulnerability in Microsoft Teams allows unauthenticated remote attackers to forge user identities and bypass authentication protections, exposing all enterprise…

How to fix or mitigate EUVD-2026-54316?

Within 24 hours: enable enhanced logging on all Teams identity and authentication operations; audit sign-in logs and token validation events for anomalous patterns indicative of identity spoofing. Within 7 days: deploy network-based monitoring rules to detect abnormal authentication flows and JWT tampering signatures; implement alerting on Teams token validation failures; communicate authentication risk to end-users and enforce mandatory credential security review. Within 30 days: establish continuous monitoring dashboards for Teams authentication anomalies; review Microsoft security advisories weekly for CVE-2026-62918 patch availability; evaluate conditional access policies and IP-based endpoint restrictions as interim containment; document all detection signatures and maintain audit trail of identity events pending vendor patch release.

Microsoft Teams EUVD-2026-54316

| CVE-2026-62918 HIGH

Improper Verification of Cryptographic Signature (CWE-347)

2026-08-07 secure@microsoft.com

GHSA-p2wf-cwq4-f5gj

Microsoft Jwt Attack Authentication Bypass Teams

7.5

CVSS 3.1 · Vendor: microsoft

Severity by source

Vendor (microsoft) PRIMARY

7.5 HIGH

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

ENISA EUVD

CRITICAL

qualitative

vuln.today AI

7.5 HIGH

Network-reachable JWT forgery requires no credentials or interaction; integrity-only impact reflects impersonation with no data exposure or disruption.

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

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (microsoft).

CVSS VectorVendor: microsoft

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Lifecycle Timeline

Analysis Generated

Aug 07, 2026 - 00:35 vuln.today

CVE Published

Aug 07, 2026 - 00:16 nvd

HIGH 7.5

DescriptionCVE.org

Improper verification of cryptographic signature in Microsoft Teams allows an unauthorized attacker to perform spoofing over a network.

AnalysisAI

Cryptographic signature spoofing in Microsoft Teams exposes enterprise collaboration environments to unauthenticated identity impersonation over the network. The flaw, tagged as a JWT attack enabling authentication bypass, allows a remote attacker with no prior credentials to forge or tamper with token-based identity claims that Teams fails to properly verify. No active exploitation has been confirmed by CISA KEV, and no public proof-of-concept has been identified at time of analysis, though the CVSS vector (AV:N/AC:L/PR:N/UI:N) indicates a low-barrier, remotely exploitable path with high integrity impact.

Technical ContextAI

The root cause is CWE-347 (Improper Verification of Cryptographic Signature), meaning Microsoft Teams does not adequately validate the cryptographic signature on tokens used to assert user or service identity. The intelligence tags - 'JWT Attack' and 'Authentication Bypass' - indicate the affected mechanism is JSON Web Token (JWT) processing, which is widely used in Microsoft's identity stack (Azure AD / Entra ID) to convey signed claims about user identity, permissions, or session state. When a JWT signature check is improperly implemented - for example, accepting unsigned tokens, accepting tokens signed with a weak or mismatched algorithm (e.g., the 'alg:none' bypass), or failing to validate the signing key - an attacker can craft arbitrary token payloads. No CPE strings were provided in the available input, so exact affected build versions cannot be enumerated from this data alone; the MSRC advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-62918 is the authoritative source for version scope.

RemediationAI

Apply the vendor-released patch by following the guidance in the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-62918 - an exact patched version number is not independently confirmed from the available data and should be verified there. Because Microsoft Teams (particularly the SaaS version) is often updated automatically by Microsoft, organizations should verify their tenant's update channel and confirm client versions are current. As a compensating control pending confirmation, security teams should enable anomalous sign-in and identity alerts in Microsoft Defender for Cloud Apps or Purview, focusing on unexpected identity changes or unusual message-sender patterns within Teams. Network-layer controls (firewall rules) are not effective mitigations, since this is an application-layer JWT handling flaw. Restricting Teams API access to known corporate IP ranges via Conditional Access policies may reduce the attack surface for unauthenticated external actors, though it does not address the root flaw.