--- title: New Managed WAF rule for Next.js CVE-2025-29927. description: Automatic deployment of a Web Application Firewall rule to block requests that attempt to bypass authentication in Next.js applications as part of CVE-2025-29927. image: https://developers.cloudflare.com/changelog-preview.png --- [Skip to content](#%5Ftop) # Changelog New updates and improvements at Cloudflare. [ Subscribe to RSS ](https://developers.cloudflare.com/changelog/rss/index.xml) [ View RSS feeds ](https://developers.cloudflare.com/fundamentals/new-features/available-rss-feeds/) ![hero image](https://developers.cloudflare.com/_astro/hero.CVYJHPAd_26AMqX.svg) [ ← Back to all posts ](https://developers.cloudflare.com/changelog/) ## New Managed WAF rule for Next.js CVE-2025-29927. Mar 22, 2025 [ Workers ](https://developers.cloudflare.com/workers/)[ Pages ](https://developers.cloudflare.com/pages/)[ WAF ](https://developers.cloudflare.com/waf/) **Update: Mon Mar 24th, 11PM UTC**: Next.js has made further changes to address a smaller vulnerability introduced in the patches made to its middleware handling. Users should upgrade to Next.js versions `15.2.4`, `14.2.26`, `13.5.10` or `12.3.6`. **If you are unable to immediately upgrade or are running an older version of Next.js, you can enable the WAF rule described in this changelog as a mitigation**. **Update: Mon Mar 24th, 8PM UTC**: Next.js has now [backported the patch for this vulnerability ↗](https://github.com/advisories/GHSA-f82v-jwr5-mffw) to cover Next.js v12 and v13\. Users on those versions will need to patch to `13.5.9` and `12.3.5` (respectively) to mitigate the vulnerability. **Update: Sat Mar 22nd, 4PM UTC**: We have changed this WAF rule to opt-in only, as sites that use auth middleware with third-party auth vendors were observing failing requests. **We strongly recommend updating your version of Next.js (if eligible)** to the patched versions, as your app will otherwise be vulnerable to an authentication bypass attack regardless of auth provider. #### Enable the Managed Rule (strongly recommended) This rule is opt-in only for sites on the Pro plan or above in the [WAF managed ruleset](https://developers.cloudflare.com/waf/managed-rules/). To enable the rule: 1. Head to Security > WAF > Managed rules in the Cloudflare dashboard for the zone (website) you want to protect. 2. Click the three dots next to **Cloudflare Managed Ruleset** and choose **Edit** 3. Scroll down and choose **Browse Rules** 4. Search for **CVE-2025-29927** (ruleId: `34583778093748cc83ff7b38f472013e`) 5. Change the **Status** to **Enabled** and the **Action** to **Block**. You can optionally set the rule to Log, to validate potential impact before enabling it. Log will not block requests. 6. Click **Next** 7. Scroll down and choose **Save** This will enable the WAF rule and block requests with the `x-middleware-subrequest` header regardless of Next.js version. #### Create a WAF rule (manual) For users on the Free plan, or who want to define a more specific rule, you can create a [Custom WAF rule](https://developers.cloudflare.com/waf/custom-rules/create-dashboard/) to block requests with the `x-middleware-subrequest` header regardless of Next.js version. To create a custom rule: 1. Head to Security > WAF > Custom rules in the Cloudflare dashboard for the zone (website) you want to protect. 2. Give the rule a name - e.g. `next-js-CVE-2025-29927` 3. Set the matching parameters for the rule match any request where the `x-middleware-subrequest` header `exists` per the rule expression below. Terminal window ``` (len(http.request.headers["x-middleware-subrequest"]) > 0) ``` 1. Set the action to 'block'. If you want to observe the impact before blocking requests, set the action to 'log' (and edit the rule later). 2. **Deploy** the rule. ![Next.js CVE-2025-29927 WAF rule](https://developers.cloudflare.com/_astro/waf-rule-cve-2025-29927.0i0XiweZ_Z8mlyw.webp) #### Next.js CVE-2025-29927 We've made a WAF (Web Application Firewall) rule available to all sites on Cloudflare to protect against the [Next.js authentication bypass vulnerability ↗](https://github.com/advisories/GHSA-f82v-jwr5-mffw) (`CVE-2025-29927`) published on March 21st, 2025. **Note**: This rule is not enabled by default as it blocked requests across sites for specific authentication middleware. * This managed rule protects sites using Next.js on Workers and Pages, as well as sites using Cloudflare to protect Next.js applications hosted elsewhere. * This rule has been made available (but not enabled by default) to all sites as part of our [WAF Managed Ruleset](https://developers.cloudflare.com/waf/managed-rules/reference/cloudflare-managed-ruleset/) and blocks requests that attempt to bypass authentication in Next.js applications. * The vulnerability affects almost all Next.js versions, and has been fully patched in Next.js `14.2.26` and `15.2.4`. Earlier, interim releases did not fully patch this vulnerability. * **Users on older versions of Next.js (`11.1.4` to `13.5.6`) did not originally have a patch available**, but this the patch for this vulnerability and a subsequent additional patch have been backported to Next.js versions `12.3.6` and `13.5.10` as of Monday, March 24th. Users on Next.js v11 will need to deploy the stated workaround or enable the WAF rule. The managed WAF rule mitigates this by blocking _external_ user requests with the `x-middleware-subrequest` header regardless of Next.js version, but we recommend users using Next.js 14 and 15 upgrade to the patched versions of Next.js as an additional mitigation.