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Cloudflare announced an emergency release of its Web Application Firewall (WAF)on October 25, 2026. This update introduces two detection rules for the Brotli vulnerability tracked asCVE-2026-111497.

These rules specifically target requests that declare Brotli body encoding and traffic accessing the Next.js image optimization endpoint. By default, both rules are enabled in Log mode, which allows for visibility without automatically blocking any matching requests.

The new detection rules have been added to the Cloudflare Managed Ruleset. However, the matching conditions include legitimate traffic, so a match does not confirm a potential exploitation attempt. Cloudflare advises customers to evaluate any matches before enabling blocking.

The first rule, identified by the suffix …ca706f3c, detects incoming requests containing the header Content-Encoding: br. This header indicates that the request body is using Brotli encoding, which means that legitimate clients submitting compressed request bodies may trigger this detection.

Cloudflare distinguishes this condition from requests that include the header Accept-Encoding: br, which the rule does not match. This update also does not change Cloudflare’s response-compression settings for Brotli, keeping request-body detection separate from response compression.

The second rule, identified by the suffix …402fe5bb, matches requests to the /_next/image endpoint used for Next.js image optimization.

This rule encompasses legitimate image optimization requests rather thantargeting solely malicious traffic. Changing this rule’s action to Block may cause optimized images to fail to load and disrupt the delivery of images in applications.

Under the default settings of the ruleset, both detection rules log matching requests without blocking them. Customers can review these matches in their analytics and configure either rule to block traffic after assessing its operational impact. Therefore, logging provides visibility rather than blocking requests that match the specified conditions.

The release announcement does not specify which software versions are affected, a vulnerability severity score, prerequisites for exploitation, or evidence of active exploitation.

Furthermore, it does not describe any potential exploit payloads. As such, the new rules should not be interpreted as proof that every matching request is targeting the vulnerability.

Cloudflare has cautioned thatexisting ruleset-level action overrides could impose immediate blocking. If an override is set to Block for the new rules, matching requests may be blocked immediately upon deployment, regardless of the default Log action. This situation could lead to false positives and disrupt legitimate traffic.

Administrators should carefully review overrides before deployment. For a more cautious rollout, Cloudflare recommends implementing rule-specific Log overrides and examining matching requests before switching to Block. This evaluation is particularly essential for applications that accept Brotli request bodies or serve images through Next.js optimization.

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