CVE-2026-55040ExploitPublished 12 Aug 2026

Hackers leverage new Microsoft SharePoint exploit in attacks

Source Bleeping Computer

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Authoritative record:CVE-2026-55040· Critical 9.1

Exploited in the wild · KEV due 21 Aug 2026 · public detection template (Nuclei) : upgrade to 16.0.5561.1001 now.

Data as of 12 Aug 2026, 12:26 UTC

CVSS 3.1 base score

9.1Critical

How severe the flaw is on the 0–10 CVSS scale.

KEV deadline: 21 Aug 2026 US federal agencies must patch by this date; a sensible deadline for everyone else. Other KEV due dates
Patch: Available – fixed in 16.0.5561.1001, 16.0.10417.20175, 16.0.19725.20434

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

Base metrics

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

Temporal metrics

Exploit Code Maturity: Unproven
Remediation Level: Official Fix
Report Confidence: Confirmed

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.
Exploit Code Maturity: Unproven: No exploit code is available, or an exploit is theoretical.
Remediation Level: Official Fix: A complete vendor solution is available. Either the vendor has issued an official patch, or an upgrade is available.
Report Confidence: Confirmed: Detailed reports exist, or functional reproduction is possible (functional exploits may provide this). Source code is available to independently verify the assertions of the research, or the author or vendor of the affected code has confirmed the presence of the vulnerability.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 14 Jul 2026
Detectable: evidence found.
nuclei template: Microsoft SharePoint Server - JWT Authentication Bypass
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: evidence found.
Listed in CISA KEV 35 days after disclosure
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

CVE ID reserved
by Microsoft Corporation
16 Jun 202614:13 UTC, 28 days before disclosure
CVE published
on cve.org
14 Jul 202617:09 UTC, t = 0
In Threat Radar
record ingested
14 Jul 202617:49 UTC, 41 minutes after disclosure
Added to CISA KEV (opens in a new tab)
exploitation confirmed
18 Aug 2026, 35 days after disclosure
KEV remediation due
US federal deadline
21 Aug 2026, 38 days after disclosure

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CISA KEV (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Microsoft SharePoint to 16.0.5561.1001 (Enterprise Server 2016) or 16.0.10417.20175 (Server 2019) or 16.0.19725.20434 (Server Subscription Edition).

Affected software

Product	Affected	Fixed in
MicrosoftMicrosoft SharePoint Enterprise Server 2016	Affected >=16.0.0 <16.0.5561.1001	Fixed in 16.0.5561.1001
MicrosoftMicrosoft SharePoint Server 2019	Affected >=16.0.0 <16.0.10417.20175	Fixed in 16.0.10417.20175
MicrosoftMicrosoft SharePoint Server Subscription Edition	Affected >=16.0.0 <16.0.19725.20434	Fixed in 16.0.19725.20434

AI-suggested

Microsoft has released an official patch for CVE-2026-55040 as part of the July 2026 Patch Tuesday updates for SharePoint Enterprise Server 2016 and SharePoint Server 2019; applying these updates is the primary mitigation. CISA recommends avoiding direct Internet exposure of SharePoint servers unless necessary, blocking external access to SharePoint Central Administration, restricting farm and database communications to required systems, and placing servers behind Layer 7 reverse proxies or similar application-layer security controls when Internet exposure is required. Security teams should follow Microsoft's official SharePoint Server security-hardening guidance. Since the vulnerability is patched, urgent application of the update is advised.

Description

A critical authentication bypass vulnerability (CVE-2026-55040) in Microsoft SharePoint has been exploited using a proof-of-concept exploit published by Rapid7. The flaw allows attackers without privileges to impersonate SharePoint users or administrators, potentially disclosing files and modifying data. Microsoft patched this vulnerability in the July 2026 Patch Tuesday updates for SharePoint Enterprise Server 2016 and SharePoint Server 2019. Although exploit code is being used in attacks, there is no confirmed widespread exploitation in the wild. CISA has issued guidance to secure SharePoint servers, including limiting Internet exposure and applying Microsoft's security hardening recommendations.

Impact

Exploitation of CVE-2026-55040 allows attackers to bypass authentication in Microsoft SharePoint, impersonate legitimate users or administrators, disclose sensitive files, and modify data. The vulnerability does not impact system availability. The availability of a public proof-of-concept exploit has led to its use in attacks, although no confirmed widespread exploitation has been reported. The vulnerability is considered an attractive target by Microsoft and has prompted warnings from CISA.

References

bleepingcomputer.com/news/microsoft/hackers-leverage-new-microsoft-sharepoint-exploit-in-attacks/ (opens in a new tab)

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Hackers leverage new Microsoft SharePoint exploit in attacks

Exploitation evidence

What to do

Affected software

Description

Impact

Nuclei detection templates

Proofs of concept on GitHub

References

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Exploitation evidence

Timeline

What to do

Affected software

Description

AI analysisMachine-generated, updated 12 Aug 2026, 12:26 UTC

Public exploits and detectiona Nuclei detection template, GitHub proofs of concept

References

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