Microsoft Entra ID

PKCE Becomes Mandatory for OAuth Public Clients as RFC 9700 and OAuth 2.1 Close Authorization Code Interception Risks

PKCE, or Proof Key for Code Exchange, was introduced in RFC 7636 to prevent code interception attacks in OAuth 2.0 flows used by mobile and single-page applications. The mechanism generates a code_verifier and derives a code_challenge using S256 hashing to bind the authorization code to the original client session. Without PKCE, malicious apps on the same device can hijack custom URI schemes like myapp://callback and exchange stolen codes for access tokens. RFC 9700, published in January 2025, now mandates PKCE for public clients and recommends it for confidential ones while requiring S256 over the weaker plain method. The upcoming OAuth 2.1 draft further embeds PKCE into the core authorization code flow and removes implicit and resource owner password credentials grants. Major providers including Auth0, Okta, and Microsoft Entra ID show varying default support, highlighting the need for explicit S256 implementation. The standard also protects against code injection attacks even when client secrets are present.

Microsoft to Make Passkeys Default Authentication in Entra ID Starting September 2026

Microsoft will transition Entra ID users to passkeys as the standard authentication method beginning September 1, 2026. The change aims to eliminate reliance on phishing-prone SMS and voice call codes. Existing SMS and voice users will be prompted to register passkeys during their next multifactor authentication. Passkeys rely on public-key cryptography and avoid shared secrets, blocking phishing, interception, credential reuse, and SIM swapping attacks. Support includes synced passkeys via iCloud Keychain and Google Password Manager, plus device-bound options like Microsoft Authenticator, Windows, and FIDO2 hardware keys. Native SMS and voice services will be fully retired on February 1, 2027, forcing affected tenants to adopt passkeys with no opt-out option.

Critical CosmosEscape Flaw Breaks Customer Isolation in Azure Cosmos DB

A critical vulnerability named CosmosEscape allowed attackers to escape the restricted Gremlin API environment and execute arbitrary code on the DB Gateway component of Azure Cosmos DB. The flaw exploited weaknesses in .NET reflection protections, enabling file read/write operations and command execution that ultimately yielded the Cosmos Master Key. With this global signing key, an attacker could retrieve the primary key for any customer account and gain full read/write access. The exploit also exposed the Config Store containing account names, subscription identifiers, tenant details, and network rules. Even network-isolated and private instances remained vulnerable because the DB Gateway itself enforced those restrictions. Internal Microsoft services including Entra ID, Teams, and Copilot rely on Cosmos DB, amplifying the potential impact of the issue.