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Next.js: Denial of Service in App Router using Server Actions

Not in CISA KEVCVE-2026-64641CWE-834

Not confirmed exploited. 2 of 8 rule sources name it; Cloudflare blocks by default.

Edge rules
2/8
Our test
No exploit yet
CVSS
8.2
EPSS
0.9% Top 42%
Posts, 14d
02026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts
Published
2026-07-27
Next.js is a React framework for building full-stack web applications. In versions 13.0.0 through 15.5.20 and 16.0.0 through 16.2.10, crafted requests targeting Next.js applications using App Router with at least one Server Action can lead… More

Next.js is a React framework for building full-stack web applications. In versions 13.0.0 through 15.5.20 and 16.0.0 through 16.2.10, crafted requests targeting Next.js applications using App Router with at least one Server Action can lead to excessive CPU usage blocking processing of further requests in the same process. This issue has been fixed in versions 15.5.21 and 16.2.11.

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Ask about CVE-2026-64641: who's covered, what to patch first, how vendors compare. I cite sources and won't help with attacks.

Workers AI (Llama 3.3). Can be wrong: check the cited source.

Severity, decoded

CVSS 4.0
High · 8.2 / 10

Exploitable over the network under specific conditions, with no privileges and no user interaction, leading to full loss of availability.

Over the internetNo login neededNo user actionWorks reliablySerious impact
How the score is built11 metrics
  • Attack vectorAn attacker can reach it over the internet; no access to your network needed.
    Network
  • Attack complexityNo built-in defences have to be bypassed; the attack works reliably.
    Low
  • Attack requirementsThe attack only works under specific conditions, such as a race or a particular setup.
    Present
  • Privileges requiredNo account or login is needed.
    None
  • User interactionNo one has to click or open anything; the attack works on its own.
    None
  • Confidentiality impact (vulnerable system)No data is exposed.
    None
  • Integrity impact (vulnerable system)Data cannot be changed by the attacker.
    None
  • Availability impact (vulnerable system)An attacker can take the component down completely or keep it from serving anyone.
    High
  • Confidentiality impact (other systems)Other systems' data is not exposed.
    None
  • Integrity impact (other systems)Other systems' data cannot be changed.
    None
  • Availability impact (other systems)Other systems keep working normally.
    None
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CISA's assessmentSSVC, from the CVE record
ExploitationNone

CISA has seen no public exploit and no attacks.

AutomatableYes

Attackers can script the attack end to end and hit many targets at once.

Technical impactPartial

A successful attack gives limited control over the affected software or limited access to its data.

Public exploits

None found
0 Metasploit0 Exploit-DB0 Scanner template0 GitHub PoCs

No exploit in Exploit-DB or Metasploit, and no scanner template. That lowers, but doesn't remove, the chance of mass exploitation.

Timeline

  1. 2026-07-21
    Cloudflare rule names it
    Earliest entry we can see is an update
  2. 2026-07-27
    CVE published
    CVE List
  3. 2026-10-21
    F5 ships a rule
    Next.js Denial of Service (3)

Social

2026-10-21: 0 posts2026-10-22: 0 posts2026-10-23: 0 posts2026-10-24: 0 posts2026-10-25: 0 posts2026-10-26: 0 posts2026-10-27: 0 posts2026-10-28: 0 posts2026-10-29: 0 posts2026-10-30: 0 posts2026-10-31: 0 posts2026-11-01: 0 posts2026-11-02: 0 posts2026-11-03: 0 posts

No posts seen yet on X, Bluesky, Mastodon, Hacker News or GitHub.

Vendor statements

Quoted
CloudflareWAF Managed Rules1 quoteBlocks by default

Named by 2026-07-21; the first entry is an update, so the rule may be older.

2026-07-21Updated…90dcdb0aDefault: BlockSource
Next.js - DoS - CVE-2026-64641. Previous action: N/A. New action: Block. This was labeled as Generic Rules - DoS.
AWSAWS WAF Managed RulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. AWS often describes a vulnerability without naming its CVE (for example "Log4j"). We count only entries that name the CVE, so AWS coverage is understated.

Microsoft AzureFront Door and Application Gateway WAF (DRS)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. The rule tables name CVEs but carry no dates, so Azure is left out of every time-to-rule figure.

Google CloudCloud Armor preconfigured WAF rulesNo public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. Google names few CVEs: the release notes start in May 2024 and the rules reference lists CVEs without dates. Its cve-canary rules are opt-in.

FastlyNext-Gen WAF virtual patchesBefore feed history

The CVE predates the oldest entry in this vendor's public feed, so a rule may exist that we cannot see.

F5Attack signatures (Distributed Cloud WAF)1 quoteRule published

First rule 2026-10-21, 86 days after the CVE was published.

2026-10-21New rule200012105Source
Added: signature 200012105 "Next.js Denial of Service (3)" (Denial of Service, risk Medium), systems: Node.js, ReactJS. References: CVE-2026-64641.
AkamaiApp & API Protector (Adaptive Security Engine)No public source

This vendor publishes no machine-readable rule changelog we can check.

OWASP CRSCore Rule Set (open source, used inside many WAFs)No public claim

We found no public statement from this vendor naming this CVE. That is not proof of no protection: generic rules may still catch it. CRS rarely names CVEs: it relies on generic detections. Our own lab measures what it actually blocks.