---
id: "CVE-2026-94543"
kind: "vulnerability"
aliases: ["CVE-2026-94543"]
title: "Next.js: cache poisoning flaw can serve attacker content to other users"
severity: "medium"
cvss: 6.3
epss: 0.00288
exploited: false
status: "open"
category: "runtime"
products: [{"name": "vercel next.js", "fixed": ["15.5.27"], "affected": ">= 15.0.0, < 15.5.27", "ecosystem": "vendor"}, {"name": "vercel next.js", "fixed": ["16.3.8"], "affected": ">= 16.0.0, < 16.3.8", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["cloudflare", "lab-disclosure", "next.js", "runtime", "self-hosted"]
not_affected_if: []
published_at: "2026-10-02T16:16:52+00:00"
first_seen_at: "2026-10-24T17:18:15+00:00"
updated_at: "2026-10-25T12:38:49+00:00"
sources: [{"source": "lab", "url": "https://developers.cloudflare.com/changelog/post/2026-10-06-waf-release/", "first_seen_at": "2026-10-24T17:18:15+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-94543", "first_seen_at": "2026-10-24T17:18:50+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-94543", "first_seen_at": "2026-10-25T12:38:49+00:00"}]
---

# Next.js: cache poisoning flaw can serve attacker content to other users

Next.js, a React framework for full-stack web apps, has a cache poisoning flaw tracked as CVE-2026-94543. The sources describe it only as cache poisoning, so an attacker may be able to make cached responses carry malicious content to other visitors.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:vercel next.js affected >= 15.0.0, < 15.5.27 fixed 15.5.27
- vendor:vercel next.js affected >= 16.0.0, < 16.3.8 fixed 16.3.8

## How to check

- Run `npx next --version` in the project and compare against the fixed versions `15.5.27` and `16.3.8`.
- Check the `next` entry in `package.json` and the lockfile for the resolved version.
- Confirm whether the app serves cached pages or responses through a CDN or cache layer.

## Fix

- Upgrade Next.js 15.x to `15.5.27` or later.
- Upgrade Next.js 16.x to `16.3.8` or later.
- Redeploy and clear any CDN or edge cache that stored responses from an affected version.

## Mitigated for you by

- Cloudflare (waf-rule): covers HTTP requests proxied through Cloudflare that match the Next.js cache poisoning exploit (Cloudflare Managed Ruleset rule ...549f7356, action Block) Limits: none stated; the document says only the rule metadata description was refined and detection is unchanged Still: none stated https://developers.cloudflare.com/changelog/post/2026-10-06-waf-release/

## Timeline

- 2026-10-24T17:18:15+00:00 lab https://developers.cloudflare.com/changelog/post/2026-10-06-waf-release/ — Cloudflare: WAF Release - 2026-10-06 · Changelog
- 2026-10-24T17:18:50+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-94543
- 2026-10-25T12:38:49+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-94543

## Documents

- [advisory] Cloudflare: WAF Release - 2026-10-06 · Changelog https://developers.cloudflare.com/changelog/post/2026-10-06-waf-release/

## From the sources

WAF Release - 2026-10-06 · Changelog

# Changelog

New updates and improvements at Cloudflare.

October 6, 2026

## WAF Release - 2026-10-06

This release introduces a new detection to mitigate a heap-based buffer overflow vulnerability in F5 BIG-IP, and enhances existing command injection protections by incorporating tested beta logic into the baseline rule.

Key Findings

- CVE-2026-94127: A heap-based buffer overflow vulnerability in F5 BIG-IP. Attackers can exploit this flaw to execute arbitrary code on the affected system.

| Ruleset | Rule ID | Legacy Rule ID | Description | Previous Action | New Action | Comments |
| --- | --- | --- | --- | --- | --- | --- |
| Cloudflare Managed Ruleset | ...a056caff | N/A | Command Injection - Generic 8 - uri - Beta | Log | Block | This rule is merged into the original rule "Command Injection - Generic 8 - uri" (ID: ...ee159e2e). |
| Cloudflare Managed Ruleset | ...7206c737 | N/A | F5 BIG-IP - UnAuth Heap-Overflow - CVE:CVE-2026-94127 | Log | Block | This is a new detection. |
| Cloudflare Managed Ruleset | ...549f7356 | N/A | Next.js - Cache Poisoning - CVE:CVE-2026-94543 | Block | Block | Rule metadata description refined. Detection unchanged. |

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_