Cyber Resilience

CVE-2026-55040

Microsoft Sharepoint Server ≤ 16.0.19725.20434

CISA KEVActive ExploitationEUVD ExploitedPublic PoC
Published
14 July 2026
Modified
19 August 2026
KEV Added
18 August 2026
Patch / advisory
View advisory
CVSS Score v3.1 9.1
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:H/A:N
EPSS Score 0.51 99th percentile
Risk Priority 93 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-55040 is a critical-severity Weak Authentication (CWE-1390) vulnerability in Microsoft Sharepoint Server. Its CVSS base score is 9.1 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Valid Accounts (T1078); ranked in the top 1% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to IA-12 (Identity Proofing) and IA-2 (Identification and Authentication (Organizational Users)) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A07:2025 Authentication Failures

EU & UK References

Vulnerability Data

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

CWE(s)
CWE-1390
KEV Date Added
18 August 2026

Related Threats

MITRE ATT&CK Enterprise Techniques

T1078 Valid Accounts Stealth
Adversaries may obtain and abuse credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion.
attack.mitre.org →
T1078.001 Default Accounts Stealth
Adversaries may obtain and abuse credentials of a default account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion.
attack.mitre.org →
T1078.002 Domain Accounts Stealth
Adversaries may obtain and abuse credentials of a domain account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion.
attack.mitre.org →
T1078.003 Local Accounts Stealth
Adversaries may obtain and abuse credentials of a local account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion.
attack.mitre.org →
T1078.004 Cloud Accounts Stealth
Valid accounts in cloud environments may allow adversaries to perform actions to achieve Initial Access, Persistence, Privilege Escalation, or Defense Evasion.
attack.mitre.org →
T1110 Brute Force Credential Access
Adversaries may use brute force techniques to gain access to accounts when passwords are unknown or when password hashes are obtained.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2023-29357Same product: Microsoft Sharepoint Serverboth on KEV
CVE-2024-38094Same product: Microsoft Sharepoint Serverboth on KEV
CVE-2023-21743Same product: Microsoft Sharepoint Server
CVE-2024-32987Same product: Microsoft Sharepoint Server
CVE-2024-49062Same product: Microsoft Sharepoint Server
CVE-2024-43466Same product: Microsoft Sharepoint Server
CVE-2023-33134Same product: Microsoft Sharepoint Server
CVE-2024-49070Same product: Microsoft Sharepoint Server
CVE-2024-21318Same product: Microsoft Sharepoint Server
CVE-2024-49064Same product: Microsoft Sharepoint Server

Affected Assets

microsoft
sharepoint server
2016, 2019 · ≤ 16.0.19725.20434

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 8 hardening rules · 6 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V7.6.1
  • V6.3.6
  • V6.4.2
  • V6.4.4

Mitigating Controls (NIST 800-53 r5) AI

IA-12 Identity Proofing good match

Requires identity proofing at appropriate assurance levels before granting accounts, directly addressing insufficient proof of identity.

IA-2 Identification and Authentication (Organizational Users) good match

Requires unique identification and authentication of users, directly stopping weak mechanisms from being used.

IA-3 Device Identification and Authentication good match

Requires device identification and authentication before establishing connections.

IA-8 Identification and Authentication (Non-organizational Users) good match

Extends strong identification and authentication requirements to non-organizational users.

IA-5 Authenticator Management good match

Mandates proper authenticator issuance, management, and strength to ensure claimed identities are verified.

AC-3 Access Enforcement partial match

Enforces access decisions based on authenticated identities, making weak authentication less exploitable.

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.AA-01 partial match
prevents

Credential management directly supports stronger authentication but does not guarantee proof of identity.

PR.AA-02 partial match
prevents

Identity proofing and binding is a core prerequisite for non-weak authentication.

PR.AA-03 partial match
prevents

Explicitly requires authentication of users/services/hardware with MFA and password-strength controls.

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.5.17 Authentication information partial match
prevents

Strong-password and non-reuse requirements raise the bar against weak single-factor authentication that can be exploited via guessing or credential stuffing.

A.8.5 Secure authentication partial match
prevents

Mandating multi-factor and non-password authentication techniques counters the use of inherently weak single-factor or password-only authentication mechanisms.

Hardening callouts derived

Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (higher-evidence rows only; rows rated `none` are excluded).

Oracle Linux 8 (1 rule)
  • V-248827 OL 8 must not have the rsh-server package installed. prevents CWE-1390
RHEL 7 (1 rule)
  • V-204442 The Red Hat Enterprise Linux operating system must not have the rsh-server package installed. prevents CWE-1390
RHEL 8 (1 rule)
  • V-230492 RHEL 8 must not have the rsh-server package installed. prevents CWE-1390
Ubuntu 22.04 (1 rule)
  • V-260470 Ubuntu 22.04 LTS, when booted, must require authentication upon booting into single-user and maintenance modes. prevents CWE-1390
Windows 10 (1 rule)
  • V-220865 The Windows Remote Management (WinRM) service must not use Basic authentication. prevents CWE-1390

References