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SameSite Cookie Blocked — Cross-Site Cookie Rejection and Third-Party Cookie Issues

Errorsecurity

Overview

Fix SameSite cookie warnings and blocked cross-site cookies affecting login sessions, payment processing, and embedded content functionality.

Key Details

  • SameSite is a cookie attribute that controls when cookies are sent in cross-site requests
  • Cookies without SameSite attribute default to SameSite=Lax in modern browsers
  • SameSite=Lax sends cookies for top-level navigation but not for cross-site sub-requests (images, iframes, AJAX)
  • SameSite=None; Secure is required for cookies that need to be sent in cross-site contexts
  • Third-party cookie deprecation in Chrome is separate from but related to SameSite enforcement

Common Causes

  • Cookie set without SameSite attribute and browser defaults it to Lax instead of None
  • Cross-origin iframe needing to access parent site cookies blocked by SameSite=Lax default
  • Payment provider redirect losing session cookies because they are cross-site requests
  • SSO (Single Sign-On) login flow failing because authentication cookies are blocked cross-site

Steps

  1. 1Identify blocked cookies: Chrome DevTools > Application > Cookies > look for yellow warning icons
  2. 2For cookies needed cross-site: set SameSite=None; Secure explicitly in the Set-Cookie header
  3. 3SameSite=None requires the Secure flag — cookies must be sent over HTTPS only
  4. 4For embedded content: use the Partitioned attribute (CHIPS) for cross-site cookies with privacy
  5. 5Test with Chrome flags: chrome://flags > search for 'SameSite' to test different enforcement levels

Tags

samesitecookiecross-sitethird-partysession

Related Items

browser-mixed-content-blocked-https

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Frequently Asked Questions

Strict: cookie only sent for same-site requests. Lax: sent for same-site plus top-level cross-site navigation (clicking a link). None: sent for all requests including cross-site sub-requests (requires Secure flag and HTTPS).