{"id":"GHSA-mg66-mrh9-m8jx","kind":"vulnerability","aliases":["GHSA-mg66-mrh9-m8jx"],"related":[],"title":"WAF and framework adapter mitigations for React and Next.js vulnerabilities · Changelog","description":"WAF and framework adapter mitigations for React and Next.js vulnerabilities · Changelog\n\n# Changelog\n\nNew updates and improvements at Cloudflare.\n\nMay 7, 2026\n\n## WAF and framework adapter mitigations for React and Next.js vulnerabilities\n\nMultiple security vulnerabilities were disclosed by the React team and Vercel affecting React Server Components and Next.js. These include denial of service, middleware and proxy bypass, server-side request forgery, cross-site scripting, and cache poisoning issues across a range of severity levels.\n\nWe strongly recommend updating your application and its dependencies immediately. Patched versions are available for React (`react-server-dom-webpack`, `react-server-dom-parcel`, and `react-server-dom-turbopack` `19.0.6`, `19.1.7`, and `19.2.6`) and Next.js (`15.5.16` and `16.2.5`).\n\n#### WAF protections\n\nCloudflare WAF rules deployed in response to prior React Server Component CVEs (`CVE-2025-55184` ↗︎ and `CVE-2026-23864` ↗︎) already provide coverage for the newly disclosed denial-of-service vulnerabilities. These rules are enabled by default with a Block action for all customers using the Cloudflare Managed Ruleset, including Free plan customers using the Free Managed Ruleset.\n\n| Ruleset | Rule description | Rule ID | Default action |\n| --- | --- | --- | --- |\n| Cloudflare Managed Ruleset | React - DoS - `CVE-2025-55184` ↗︎ | `2694f1610c0b471393b21aef102ec699` | Disabled |\n| Cloudflare Managed Ruleset | React - DoS - `CVE-2026-23864` ↗︎ | `aaede80b4d414dc89c443cea61680354` | Block |\n\nThe existing rules detect the underlying attack patterns generically. As a result, they apply to the new `CVE-2026-23870` ↗︎ denial-of-service vulnerability in Server Components and the corresponding Next.js advisory `GHSA-8h8q-6873-q5fj` ↗︎.\n\nCloudflare is investigating whether WAF rules can be safely and effectively deployed for three of the high-severity advisories: `CVE-2026-23870` ↗︎ / `GHSA-8h8q-6873-q5fj` ↗︎, `GHSA-267c-6grr-h53f` ↗︎, and `GHSA-mg66-mrh9-m8jx` ↗︎. If it is possible to create a managed WAF rule that mitigates these CVEs and does not potentially break application behavior, Cloudflare will add additional managed WAF rules. These rules will be announced through the WAF changelog. Because these vulnerabilities were shared with Cloudflare with minimal advance notice, we are still investigating what WAF mitigations are possible.\n\nSeveral of the disclosed vulnerabilities are not possible to block in WAF. We strongly recommend updating your applications so they are not purely reliant on WAF mitigations.\n\nCustomers on Pro, Business, or Enterprise plans should ensure that Managed Rules are enabled.\n\n#### Next.js adapters\n\nVinext: Vinext ↗︎ is a Vite plugin that reimplements the Next.js API surface. Vinext's latest release is not vulnerable to any of the disclosed CVEs. Vinext's architecture differs from stock Next.js in ways that sidestep the affected code paths. For example, it does not implement the PPR resume protocol, does not expose Pages Router data-route endpoints, and strips internal headers such as `x-nextjs-data` at request boundaries. As an extra layer of defense, we added a React `19.2.6` or later requirement when running `vinext init` (PR #1118 ↗︎, PR #1112 ↗︎) to prevent accidentally running a vulnerable version of React with Vinext.\n\nOpenNext on Cloudflare: OpenNext is an adapter that lets you deploy Next.js apps to the Cloudflare Workers platform. OpenNext itself is not directly vulnerable to the React denial-of-service CVE, but users must update the Next.js version in their application. The OpenNext team has updated the adapter to further harden against these vectors and released a new version of the Cloudflare adapter. Test fixtures and examples have been updated to use patched versions (PR #1255 ↗︎).\n\n#### Summary of disclosed vulnerabilities\n\n| Advisory | Severity | Issue | WAF status |\n| --- | --- | --- | --- |\n| `CVE-2026-23870` ↗︎ / `GHSA-8h8q-6873-q5fj` ↗︎ | High | Denial of service in Server Components | WAF rules in place: `2694f1610c0b471393b21aef102ec699`, `aaede80b4d414dc89c443cea61680354` Cloudflare is investigating additional managed WAF coverage |\n| `GHSA-267c-6grr-h53f` ↗︎ | High | Middleware bypass via segment-prefetch routes | Cloudflare is investigating if this can be safely and effectively mitigated by a managed WAF rule |\n| `GHSA-mg66-mrh9-m8jx` ↗︎ | High | Denial of service via connection exhaustion in Cache Components | Cloudflare is investigating if this can be safely and effectively mitigated by a managed WAF rule |\n| `GHSA-492v-c6pp-mqqv` ↗︎ | High | Middleware bypass via dynamic route parameter injection | Not possible to safely enable a managed WAF rule without potentially breaking application behavior |\n| `GHSA-c4j6-fc7j-m34r` ↗︎ | High | SSRF via WebSocket upgrades | Not possible to safely enable a managed WAF rule without potentially breaking application behavior |\n| `GHSA-36qx-fr4f-26g5` ↗︎ | High | Middleware bypass in Pages Router i18n | Custom WAF rule possible; global managed rule could potentially break application behavior |\n| `GHSA-ffhc-5mcf-pf4q` ↗︎ | Moderate | XSS via CSP nonces | Custom WAF rule possible; global managed rule could potentially break application behavior |\n| `GHSA-gx5p-jg67-6x7h` ↗︎ | Moderate | XSS in `beforeInteractive` scripts | Not possible to safely enable a managed WAF rule without potentially breaking application behavior |\n| `GHSA-h64f-5h5j-jqjh` ↗︎ | Moderate | Denial of service in Image Optimization API | Custom WAF rule possible; global managed rule could potentially break application behavior |\n| `GHSA-wfc6-r584-vfw7` ↗︎ | Moderate | Cache poisoning in RSC responses | Custom WAF rule possible; global managed rule could potentially break application behavior |\n| `GHSA-vfv6-92ff-j949` ↗︎ | Low | Cache poisoning via RSC cache-busting collisions | Not possible to safely enable a managed WAF rule without potentially breaking application behavior |\n| `GHSA-3g8h-86w9-wvmq` ↗︎ | Low | Middleware redirect cache poisoning | Custom WAF rule possible; global managed rule could potentially break application behavior |","summary":"This Cloudflare changelog entry covers a high-severity denial-of-service flaw in React Server Components and Next.js Cache Components (GHSA-mg66-mrh9-m8jx) that exhausts connections. Cloudflare says it is still investigating whether a managed WAF rule can block it safely.","severity":"high","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["cloudflare","cloudflare-workers","lab-disclosure","next.js","react","self-hosted","vendor"],"not_affected_if":["no-react-server-components","static-export"],"how_to_check":"- Check the React packages with `npm ls react-server-dom-webpack react-server-dom-parcel react-server-dom-turbopack`\n- Check the Next.js version with `npx next --version`\n- Look for Cache Components enabled in the Next.js configuration","fix":"- Update React server DOM packages to `19.0.6`, `19.1.7`, or `19.2.6` depending on the release line\n- Update Next.js to `15.5.16` or `16.2.5`\n- Keep Cloudflare Managed Rules enabled, but do not rely on the WAF alone for this flaw","status":"open","published_at":"2026-05-07T00:00:00+00:00","first_seen_at":"2026-10-24T18:56:54+00:00","triaged_at":"2026-10-25T05:35:38+00:00","updated_at":"2026-10-25T05:35:38+00:00","category":"vendor","confidence":0.6,"triage":{"at":"2026-10-25T05:35:38Z","model":"claude-haiku-5-5","output":{"fix":"- Update React server DOM packages to `19.0.6`, `19.1.7`, or `19.2.6` depending on the release line\n- Update Next.js to `15.5.16` or `16.2.5`\n- Keep Cloudflare Managed Rules enabled, but do not rely on the WAF alone for this flaw","reach":"internet","title":"Next.js and React: Cache Components connection exhaustion denial of service","impact":"medium","summary":"This Cloudflare changelog entry covers a high-severity denial-of-service flaw in React Server Components and Next.js Cache Components (GHSA-mg66-mrh9-m8jx) that exhausts connections. Cloudflare says it is still investigating whether a managed WAF rule can block it safely.","category":"vendor","nicknames":[],"who_cares":["next.js","react","self-hosted","cloudflare-workers"],"confidence":0.6,"needs_auth":"unknown","worst_case":"Attacker exhausts server connections, taking the application offline","analyst_note":"Find the upstream GHSA-mg66-mrh9-m8jx advisory for affected version ranges and whether Cache Components is required to be exploitable.","how_to_check":"- Check the React packages with `npm ls react-server-dom-webpack react-server-dom-parcel react-server-dom-turbopack`\n- Check the Next.js version with `npx next --version`\n- Look for Cache Components enabled in the Next.js configuration","needs_analyst":true,"not_affected_if":["static-export","no-react-server-components"],"who_is_affected":"Applications that use React Server Components or Next.js with Cache Components are affected. Cloudflare says a WAF rule for this specific advisory is still under investigation, and some of the disclosed flaws cannot be blocked by WAF at all. Sites not using these frameworks can skip it.","user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000917,"input_tokens":5803,"output_tokens":673,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2025':212C,270C '-2026':216C,280C,302C,343C,653C '-23864':217C,281C '-23870':303C,344C,654C '-55184':213C,271C '1112':554C '1118':552C '1255':642C '15.5.16':194C '16.2.5':196C '19.0.6':188C '19.1.7':189C '19.2.6':191C,543C '2026':100C '267c':352C '2694f1610c0b471393b21aef102ec699':272C '6873':320C,348C,658C '6grr':353C '7':99C '8h8q':319C,347C,657C 'aaede80b4d414dc89c443cea61680354':282C 'accident':557C 'across':150C 'action':239C,263C 'adapt':4A,83C,104C,460C,572C,614C,629C 'add':384C,540C 'addit':385C 'advanc':407C 'advisori':316C,341C,647C 'affect':122C,498C 'alreadi':218C 'announc':393C 'api':471C 'app':578C 'appli':297C 'applic':161C,380C,435C,607C 'architectur':488C 'attack':290C 'avail':169C 'behavior':381C 'block':77B,238C,283C,427C 'boundari':532C 'break':379C 'busi':448C 'bypass':136C 'cach':55B,147C 'changelog':11A,37B,90C,91C,397C 'cloudflar':22B,24B,36B,65B,97C,199C,245C,264C,274C,322C,382C,404C,568C,581C,628C 'cloudflare-work':23B 'code':499C 'compon':52B,56B,125C,209C,311C 'connect':64B 'correspond':314C 'cover':39B 'coverag':220C 'creat':366C 'cross':143C 'cross-sit':142C 'custom':242C,251C,445C 'cve':211C,215C,269C,279C,301C,342C,597C,652C 'cves':210C,374C,485C 'data':517C,529C 'data-rout':516C 'default':235C,262C 'defens':538C 'denial':45B,130C,226C,305C,594C,661C 'denial-of-servic':44B,225C,304C,593C 'depend':164C 'deploy':202C,333C,576C 'descript':259C 'detect':287C 'differ':489C 'direct':588C 'disabl':273C 'disclos':115C,224C,421C,484C,645C 'disclosur':28B 'dom':175C,180C,186C 'dos':268C,278C 'effect':332C 'enabl':233C,458C 'endpoint':519C 'ensur':453C 'enterpris':450C 'entri':38B 'exampl':502C,633C 'exhaust':63B 'exist':285C 'expos':513C 'extra':535C 'fixtur':631C 'flaw':48B 'forgeri':141C 'framework':3A,82C,103C 'free':249C,254C 'generic':292C 'ghsa':13A,18A,58B,318C,346C,351C,357C,656C 'ghsa-267c-6grr-h53f':350C 'ghsa-8h8q':317C,345C,655C 'ghsa-mg66-mrh9-m8jx':12A,17A,57B,356C 'h53f':354C 'harden':617C 'header':523C 'high':42B,339C,660C 'high-sever':41B,338C 'host':33B 'id':261C 'immedi':165C 'implement':506C 'improv':95C 'includ':129C,248C 'init':550C 'intern':522C 'investig':70B,324C,412C 'issu':149C,649C 'lab':27B 'lab-disclosur':26B 'later':545C 'latest':475C 'layer':536C 'let':574C 'level':155C 'm8jx':16A,21A,61B,360C 'manag':73B,246C,255C,265C,275C,368C,386C,455C 'may':98C 'mg66':14A,19A,59B,358C 'middlewar':133C 'minim':406C 'mitig':5A,84C,105C,372C,415C,444C 'mrh9':15A,20A,60B,359C 'multipl':111C 'must':600C 'new':92C,300C,624C 'newli':223C 'next.js':9A,29B,54B,88C,109C,127C,193C,315C,459C,470C,492C,577C,603C 'nextj':528C 'notic':408C 'opennext':566C,569C,584C,609C 'page':514C 'parcel':181C 'patch':166C,639C 'path':500C 'pattern':291C 'plan':250C,451C 'platform':583C 'plugin':466C 'poison':148C 'possibl':364C,417C,425C 'potenti':378C 'ppr':508C 'pr':551C,553C,641C 'prevent':556C 'prior':206C 'pro':447C 'protect':198C 'protocol':510C 'provid':219C 'proxi':135C 'pure':440C 'q5fj':321C,349C,659C 'rang':152C 'react':7A,30B,50B,86C,107C,118C,123C,171C,173C,178C,184C,207C,267C,277C,542C,563C,592C 'react-server-dom-parcel':177C 'react-server-dom-turbopack':183C 'react-server-dom-webpack':172C 'recommend':158C,432C 'reimplement':468C 'releas':476C,622C 'reliant':441C 'request':140C,531C 'requir':546C 'respons':204C 'result':295C 'resum':509C 'rout':518C 'router':515C 'rule':75B,201C,231C,258C,260C,286C,327C,370C,388C,390C,456C 'ruleset':247C,256C,257C,266C,276C 'run':548C,558C 'safe':79B,330C 'say':66B 'script':145C 'se':663C 'secur':112C 'self':32B 'self-host':31B 'server':51B,124C,138C,174C,179C,185C,208C,310C 'server-sid':137C 'servic':47B,132C,228C,307C,596C 'sever':43B,154C,340C,418C,648C 'share':402C 'side':139C 'sidestep':496C 'site':144C 'status':651C 'still':69B,411C 'stock':491C 'strip':521C 'strong':157C,431C 'summari':643C 'surfac':472C 'team':119C,610C 'test':630C 'three':335C 'turbopack':187C 'under':289C 'updat':93C,159C,433C,601C,612C,636C 'use':243C,252C,638C 'user':599C 'vector':620C 'vendor':34B 'vercel':121C 'version':167C,561C,604C,625C,640C 'vinext':461C,462C,473C,486C,549C,565C 'vite':465C 'vulner':10A,89C,110C,113C,229C,308C,400C,422C,479C,560C,589C,646C 'waf':1A,74B,80C,101C,197C,200C,326C,369C,387C,396C,414C,429C,443C,650C 'way':494C 'webpack':176C 'whether':71B,325C 'worker':25B,582C 'x':527C 'x-nextjs-data':526C","nicknames":[],"mitigations":[],"who_affected":"Applications that use React Server Components or Next.js with Cache Components are affected. Cloudflare says a WAF rule for this specific advisory is still under investigation, and some of the disclosed flaws cannot be blocked by WAF at all. Sites not using these frameworks can skip it.","tier":"B","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-05-07T00:00:00+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"lab","external_id":"https://developers.cloudflare.com/changelog/post/2026-05-06-react-nextjs-vulnerabilities/#GHSA-mg66-mrh9-m8jx","url":"https://developers.cloudflare.com/changelog/post/2026-05-06-react-nextjs-vulnerabilities/","severity":null,"published_at":"2026-05-07T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-24T18:56:54+00:00","fetched_at":"2026-10-24T18:56:54+00:00","note":"Cloudflare: WAF and framework adapter mitigations for React and Next.js vulnerabilities · Changelog"}],"documents":[{"id":2906,"url":"https://developers.cloudflare.com/changelog/post/2026-05-06-react-nextjs-vulnerabilities/","title":"Cloudflare: WAF and framework adapter mitigations for React and Next.js vulnerabilities · Changelog","kind":"advisory","source":"lab","text":"WAF and framework adapter mitigations for React and Next.js vulnerabilities · Changelog\n\n# Changelog\n\nNew updates and improvements at Cloudflare.\n\nMay 7, 2026\n\n## WAF and framework adapter mitigations for React and Next.js vulnerabilities\n\nMultiple security vulnerabilities were disclosed by the React team and Vercel affecting React Server Components and Next.js. These include denial of service, middleware and proxy bypass, server-side request forgery, cross-site scripting, and cache poisoning issues across a range of severity levels.\n\nWe strongly recommend updating your application and its dependencies immediately. Patched versions are available for React (`react-server-dom-webpack`, `react-server-dom-parcel`, and `react-server-dom-turbopack` `19.0.6`, `19.1.7`, and `19.2.6`) and Next.js (`15.5.16` and `16.2.5`).\n\n#### WAF protections\n\nCloudflare WAF rules deployed in response to prior React Server Component CVEs (`CVE-2025-55184` ↗︎ and `CVE-2026-23864` ↗︎) already provide coverage for the newly disclosed denial-of-service vulnerabilities. These rules are enabled by default with a Block action for all customers using the Cloudflare Managed Ruleset, including Free plan customers using the Free Managed Ruleset.\n\n| Ruleset | Rule description | Rule ID | Default action |\n| --- | --- | --- | --- |\n| Cloudflare Managed Ruleset | React - DoS - `CVE-2025-55184` ↗︎ | `2694f1610c0b471393b21aef102ec699` | Disabled |\n| Cloudflare Managed Ruleset | React - DoS - `CVE-2026-23864` ↗︎ | `aaede80b4d414dc89c443cea61680354` | Block |\n\nThe existing rules detect the underlying attack patterns generically. As a result, they apply to the new `CVE-2026-23870` ↗︎ denial-of-service vulnerability in Server Components and the corresponding Next.js advisory `GHSA-8h8q-6873-q5fj` ↗︎.\n\nCloudflare is investigating whether WAF rules can be safely and effectively deployed for three of the high-severity advisories: `CVE-2026-23870` ↗︎ / `GHSA-8h8q-6873-q5fj` ↗︎, `GHSA-267c-6grr-h53f` ↗︎, and `GHSA-mg66-mrh9-m8jx` ↗︎. If it is possible to create a managed WAF rule that mitigates these CVEs and does not potentially break application behavior, Cloudflare will add additional managed WAF rules. These rules will be announced through the WAF changelog. Because these vulnerabilities were shared with Cloudflare with minimal advance notice, we are still investigating what WAF mitigations are possible.\n\nSeveral of the disclosed vulnerabilities are not possible to block in WAF. We strongly recommend updating your applications so they are not purely reliant on WAF mitigations.\n\nCustomers on Pro, Business, or Enterprise plans should ensure that Managed Rules are enabled.\n\n#### Next.js adapters\n\nVinext: Vinext ↗︎ is a Vite plugin that reimplements the Next.js API surface. Vinext's latest release is not vulnerable to any of the disclosed CVEs. Vinext's architecture differs from stock Next.js in ways that sidestep the affected code paths. For example, it does not implement the PPR resume protocol, does not expose Pages Router data-route endpoints, and strips internal headers such as `x-nextjs-data` at request boundaries. As an extra layer of defense, we added a React `19.2.6` or later requirement when running `vinext init` (PR #1118 ↗︎, PR #1112 ↗︎) to prevent accidentally running a vulnerable version of React with Vinext.\n\nOpenNext on Cloudflare: OpenNext is an adapter that lets you deploy Next.js apps to the Cloudflare Workers platform. OpenNext itself is not directly vulnerable to the React denial-of-service CVE, but users must update the Next.js version in their application. The OpenNext team has updated the adapter to further harden against these vectors and released a new version of the Cloudflare adapter. Test fixtures and examples have been updated to use patched versions (PR #1255 ↗︎).\n\n#### Summary of disclosed vulnerabilities\n\n| Advisory | Severity | Issue | WAF status |\n| --- | --- | --- | --- |\n| `CVE-2026-23870` ↗︎ / `GHSA-8h8q-6873-q5fj` ↗︎ | High | Denial of service in Server Components | WAF rules in place: `2694f1610c0b471393b21aef102ec699`, `aaede80b4d414dc89c443cea61680354` Cloudflare is investigating additional managed WAF coverage |\n| `GHSA-267c-6grr-h53f` ↗︎ | High | Middleware bypass via segment-prefetch routes | Cloudflare is investigating if this can be safely and effectively mitigated by a managed WAF rule |\n| `GHSA-mg66-mrh9-m8jx` ↗︎ | High | Denial of service via connection exhaustion in Cache Components | Cloudflare is investigating if this can be safely and effectively mitigated by a managed WAF rule |\n| `GHSA-492v-c6pp-mqqv` ↗︎ | High | Middleware bypass via dynamic route parameter injection | Not possible to safely enable a managed WAF rule without potentially breaking application behavior |\n| `GHSA-c4j6-fc7j-m34r` ↗︎ | High | SSRF via WebSocket upgrades | Not possible to safely enable a managed WAF rule without potentially breaking application behavior |\n| `GHSA-36qx-fr4f-26g5` ↗︎ | High | Middleware bypass in Pages Router i18n | Custom WAF rule possible; global managed rule could potentially break application behavior |\n| `GHSA-ffhc-5mcf-pf4q` ↗︎ | Moderate | XSS via CSP nonces | Custom WAF rule possible; global managed rule could potentially break application behavior |\n| `GHSA-gx5p-jg67-6x7h` ↗︎ | Moderate | XSS in `beforeInteractive` scripts | Not possible to safely enable a managed WAF rule without potentially breaking application behavior |\n| `GHSA-h64f-5h5j-jqjh` ↗︎ | Moderate | Denial of service in Image Optimization API | Custom WAF rule possible; global managed rule could potentially break application behavior |\n| `GHSA-wfc6-r584-vfw7` ↗︎ | Moderate | Cache poisoning in RSC responses | Custom WAF rule possible; global managed rule could potentially break application behavior |\n| `GHSA-vfv6-92ff-j949` ↗︎ | Low | Cache poisoning via RSC cache-busting collisions | Not possible to safely enable a managed WAF rule without potentially breaking application behavior |\n| `GHSA-3g8h-86w9-wvmq` ↗︎ | Low | Middleware redirect cache poisoning | Custom WAF rule possible; global managed rule could potentially break application behavior |","published_at":"2026-05-07T00:00:00+00:00","relation":"advisory","confidence":null,"note":null}],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}