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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallOasis Security reported a flaw in Microsoft’s multi-factor authentication (MFA) sign-in flow that let someone with a valid password keep guessing six-digit authenticator codes by opening fresh sign-in sessions. Oasis said the failed attempts did not alert account owners. The researchers’ timeline says Microsoft deployed a permanent fix on October 9, 2024; this is a historical, reportedly resolved issue, not evidence of a currently unpatched Azure vulnerability.
What was the Microsoft Azure MFA flaw?
Despite “Azure” in the report’s title, Oasis described a weakness in Microsoft’s MFA verification flow, affecting sign-ins to Microsoft accounts and services that included Outlook, OneDrive, Teams and Azure Cloud. The available account does not establish that the flaw was isolated to Azure infrastructure.
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In the scenario Oasis described, an attacker first needed a valid email address and password. After that, the sign-in process asked for a six-digit authenticator code. Oasis said up to 10 consecutive incorrect codes were allowed in a single session. By rapidly creating new sessions, researchers could make additional guesses rather than being stopped by the per-session limit. Oasis also reported that the failed attempts did not generate alerts to the account owner.
This was a weakness in the second-factor verification and its rate limiting—not a way to sign in without a password. Oasis reported researcher demonstrations; the cited account does not establish criminal exploitation or prove that accounts were compromised.
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- FAST & CONVENIENT LOGIN: Plug in your Security Key C NFC via USB-C and tap it, or tap it against your phone (NFC) to authenticate. No batteries, no internet connection, and no extra fees required.
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Why did the code’s validity window matter?
Oasis reported that, in its testing of Microsoft sign-in, a time-based code was tolerated for around three minutes—about 2.5 minutes beyond its expiry according to the report. That is a finding about the sign-in flow Oasis tested, not a general property of authenticator apps or all time-based one-time password systems.
The IETF’s RFC 6238 specifies a default TOTP time-step size of 30 seconds. It also allows a validator to account for transmission delay and cautions that accepting codes over a wider window increases the opportunity for an attacker to guess one. The 30-second time step is not a guarantee that every system accepts a code for exactly 30 seconds; it is distinct from Oasis’s reported observation of Microsoft’s acceptance window.
Rank #2
- POWERFUL SECURITY KEY: The YubiKey 5C NFC is the most versatile physical passkey, protecting your digital life from phishing attacks. It ensures only you can access your accounts
- WORKS WITH 1000+ ACCOUNTS: Compatible with popular accounts like Google, Microsoft, and Apple. A single YubiKey 5C NFC secures 100+ of your favorite accounts, including email, password managers, and more
- FAST & CONVENIENT LOGIN: Plug in your YubiKey 5C NFC via USB and tap it, or tap it against your phone (NFC), to authenticate. No batteries, no internet connection, and no extra fees required
- MOST SECURE PASSKEY: Supports FIDO2/WebAuthn, FIDO U2F, Yubico OTP, OATH-TOTP/HOTP, Smart card (PIV), and OpenPGP. That means it’s versatile, working almost anywhere you need it
- PRIMARY & SPARE KEYS: Just like having a spare house key, we recommend buying two YubiKeys - one for daily use and one as a spare. That way you’ll never get locked out of your accounts
What is the reported fix timeline?
| Date | Action reported by Oasis Security |
|---|---|
| June 24, 2024 | Microsoft acknowledged the issue. |
| July 4, 2024 | Microsoft deployed a temporary fix. |
| October 9, 2024 | Microsoft deployed a permanent fix. |
Oasis says the specific technical changes are confidential. It reports that Microsoft introduced a stricter rate limit after a number of failed attempts, with the strict limit lasting around half a day. The report says the issue had been fixed before it was published on December 11, 2024. These remediation details and dates are Oasis’s account.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsWhat should Microsoft 365 and Entra administrators do?
Oasis’s recommendations are useful as general account-security practices, not as evidence that any particular tenant was affected or compromised:
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- POWERFUL SECURITY KEY: The YubiKey 5 NFC is the most versatile physical passkey, protecting your digital life from phishing attacks. It ensures only you can access your accounts
- WORKS WITH 1000+ ACCOUNTS: Compatible with popular accounts like Google, Microsoft, and Apple. A single YubiKey 5 NFC secures 100+ of your favorite accounts, including email, password managers, and more
- FAST & CONVENIENT LOGIN: Plug in your YubiKey 5 NFC via USB and tap it, or tap it against your phone (NFC), to authenticate. No batteries, no internet connection, and no extra fees required
- MOST SECURE PASSKEY: Supports FIDO2/WebAuthn, FIDO U2F, Yubico OTP, OATH-TOTP/HOTP, Smart card (PIV), and OpenPGP. That means it’s versatile, working almost anywhere you need it
- PRIMARY & SPARE KEYS: Just like having a spare house key, we recommend buying two YubiKeys - one for daily use and one as a spare. That way you’ll never get locked out of your accounts
- Keep MFA enabled for user accounts.
- Monitor failed second-factor attempts and configure alerts for suspicious patterns where your identity and logging setup supports them.
- Consider passwordless sign-in methods where they fit your organization’s policies, devices and recovery processes. Microsoft’s Entra authentication-method guidance is the place to check current options and policy requirements.
- Ensure users have a workable account-recovery and support path before changing sign-in methods.
Passwordless authentication can reduce reliance on manually entered, short-lived codes, but the right method depends on configured Entra policies, user devices and recovery needs. A hardware security key is not a repair for this historical server-side rate-limit weakness; it is one possible authentication method to evaluate against your environment.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How widespread was the potential exposure?
Microsoft CEO Satya Nadella said on the January 30, 2024 FY2024 Q2 earnings call, “We now have more than 400 million paid Office 365 seats.” That figure describes Microsoft’s paid Office 365 seat base at that time. It is not a count of accounts shown to be vulnerable, attacked or compromised, and should not be treated as one.
Quick Recap
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- POWERFUL SECURITY KEY: The Security Key NFC is the essential physical passkey for protecting your digital life from phishing attacks. It ensures only you can access your accounts.
- WORKS WITH 1000+ ACCOUNTS: Compatible with Google, Microsoft, and Apple. A single Security Key NFC secures 100 of your favorite accounts, including email, password managers, and more.
- FAST & CONVENIENT LOGIN: Plug in your Security Key NFC via USB-A and tap it, or tap it against your phone (NFC) to authenticate. No batteries, no internet connection, and no extra fees required.
- TRUSTED PASSKEY TECHNOLOGY: Uses the latest passkey standards (FIDO2/WebAuthn & FIDO U2F) but does not support One-Time Passwords. For complex needs, check out the YubiKey 5 Series.
- BUILT TO LAST: Made from tough, waterproof, and crush-resistant materials. Manufactured in Sweden and programmed in the USA with the highest security standards.
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