How severe is CVE-2026-27977?

No CVSS score has been assigned to CVE-2026-27977 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-27977?

CVE-2026-27977 affects the following packages: next (npm). Ecosystems affected: npm.

How do I fix CVE-2026-27977?

Update next to 16.1.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27977 is resolved across your whole dependency graph.

How do I detect CVE-2026-27977 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for next, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-27977 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-27977 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-27977 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-27977?

CVE-2026-27977 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 8th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-27977?

CVE-2026-27977 is classified as CWE-1385 (CWE-1385). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-27977 published, and has it been updated?

CVE-2026-27977 was published on March 17, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2026-27977 — next

Fix: vercel/next.js@862f9b9

CVE-2026-27977 is a CWE-1385 vulnerability in next. A fix is available for next — see the affected versions and patch details below.

Next.js: null origin can bypass dev HMR websocket CSRF checks

Also known asGHSA-jcc7-9wpm-mj36

Published

Mar 17, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27977.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk+0.00%

Lower risk than most CVEs8th percentile — riskier than 8% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

61Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

nextnpm

91.0Mdownloads / week

Description

Summary

In next dev, cross-site protections for internal development endpoints could treat Origin: null as a bypass case even when allowedDevOrigins is configured. This could allow privacy-sensitive or opaque browser contexts, such as sandboxed documents, to access privileged internal dev-server functionality unexpectedly.

Impact

If a developer visits attacker-controlled content while running an affected next dev server with allowedDevOrigins configured, attacker-controlled browser code may be able to connect to internal development endpoints and interact with sensitive dev-server functionality that should have remained blocked.

This issue affects development mode only. It does not affect next start, and it does not expose internal debugging functionality to the network by default.

Patches

Fixed by validating Origin: null through the same cross-site origin-allowance checks used for other origins on internal development endpoints.

Workarounds

If upgrade is not immediately possible:

Do not expose next dev to untrusted networks.
If you use allowedDevOrigins, reject requests and websocket upgrades with Origin: null for internal dev endpoints at your proxy.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`next`	≥ 16.0.1&&< 16.1.7	16.1.7`npm install next@16.1.7`

Affected Products

1 product · 1 configurations

Application

next.jsvercel

≥ 16.0.1 && < 16.1.7

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for next, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update next to 16.1.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27977 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-27977 (CC BY 4.0)

Frequently Asked Questions

## Summary In `next dev`, cross-site protections for internal development endpoints could treat `Origin: null` as a bypass case even when [`allowedDevOrigins`](https://nextjs.org/docs/app/api-reference/config/next-config-js/allowedDevOrigins) is configured. This could allow privacy-sensitive or opaque browser contexts, such as sandboxed documents, to access privileged internal dev-server functionality unexpectedly. ## Impact If a developer visits attacker-controlled content while running an affected `next dev` server with [`allowedDevOrigins`](https://nextjs.org/docs/app/api-reference/config/

O3 Security · Impact-Aware SCA

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