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Dossier · Vulnerability

Actively exploited · CISA KEV · NVD published 2026-07-14

CVE-2026-55040

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

  1. KEV
  2. 105 days →First PoC

Signals

Exploited in the wild
Yesadded 2026-08-18 · due 2026-08-21. An observation, not a forecast.
EPSS · 30-day forecast
70%Chance of exploitation in the next 30 days, 99th percentile of all CVEs. A forecast; KEV outranks it.
CVSS · NVD · CRITICAL
9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Internet exposure
not stated by sourcesNo exposure census on this CVE's dispatches.

Exploits

6 known · links only

GitHub PoCs · by trust, then stars5

  1. sfewer-r7/CVE-2026-55040 ↗Trust ok 100

    Microsoft SharePoint JWT Authentication Bypass (CVE-2026-55040)

    ★ 59 · created 2026-08-06

  2. l0ggg/CVE-2026-55040 ↗Trust ok 100

    Exploit code for CVE-2026-55040, it can create auth header for any validate account.

    ★ 3 · created 2026-07-28

  3. maxprog-svg/CVE-2026-55040-Mass-Exploit ↗Trust ok 100

    CVE-2026-55040

    ★ 0 · created 2026-08-27

  4. virologi-info/mssharepoint-scanner ↗Trust ok 100

    A scanner for CVE-2026-55040 and CVE-2026-63520, designed to determine whether the server is affected by these two CVEs.

    ★ 0 · created 2026-08-27

  5. zenzue/CVE-2026-55040 ↗Trust ok 100

    ★ 0 · created 2026-08-26

Fake proof-of-concept repositories have been used to deliver malware to the researchers who run them. The trust verdict is our engine's heuristic over the repository (account age, what it ships, how its stars arrived); it is a reason to read the code first, not a finding about its author.

Nuclei1

  1. Microsoft SharePoint Server - JWT Authentication Bypass ↗

    Microsoft SharePoint Server is vulnerable to an authentication bypass (CVE-2026-55040) in its JWT token validation pipeline (SPJsonWebSecurityTokenHandlerV2). The chain disables signature requirements (RequireSignedTokens=false, accepting alg:none tokens), resolves the actor token x5t thumbprint against the server's own STS signing certificate (freely retrievable from /_layouts/15/metadata/json/1) without verifying the signature, accepts unregistered certificate issuers, and only checks the acto

    yaml · seen 2026-10-18

On the wire

2 dispatches
  1. Rapid7 Analysis: Microsoft SharePoint JWT Token Authentication Bypass (CVE-2026-55040)KEV
  2. Rapid7 Analysis: Microsoft SharePoint Remote Code Execution (CVE-2026-63520)KEV

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