#44 - The Badge That Printed Itself: The SharePoint Token Forgery, Decoded (CVE-2026-55040)

The Badge That Printed Itself: A SharePoint TokenForgery, Decoded Word by Word
One line from my morning threat intel digest: “CVE-2026-55040. Critical. CVSS 9.1. SharePoint on-prem authentication bypass, under active exploitation.” This episode stops and takes the whole sentence apart, from first principles, until it reads likeplain English. Then we walk the heist: how a stranger with no account and no password handed SharePoint a homemade admin token, and SharePoint said welcome back.

In this episode:
• Decoding the line: CVE, CVSS, KEV, on-prem, auth bypass, PoC, and why an n-day means the attacker is racing your change board
• What a token is, explained so the bug becomes obvious
• The heist in four dominoes: alg “none”, the x5t pointer aimed at SharePoint’s own certificate, circular trust, and a signature that just says “AAAA”
• Textbook Swiss cheese, and why four checks that share one assumption are really one check
• Why forged tokens are quieter than stolen ones, and the three places you can still catch them
• The out-of-the-loop identity platform: your MFA and conditional access were never beaten, they were never asked
• Should you ever roll your own token validator? The steelman, the verdict, and the architecture I’d build instead

LinkedIn: ⁠linkedin.com/in/rohit-agnihotri⁠
Email: theIdentityNavigator@gmail.com