VulnerabilityPublished 17 Mar 2026

CVE-2026-27977: vercel next.js · Missing Origin Validation in WebSockets

Affects vercel next.jsSource CVE Database V5

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Not known to be exploited · CVSS 2.3 Low : upgrade to 16.1.7 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score

2.3Low

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 7% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 16.1.7

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
User Interaction: Passive
Vulnerable system confidentiality: Low
Vulnerable system integrity: Low
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: Passive: Successful exploitation of this vulnerability requires limited interaction by the targeted user with the vulnerable system and the attacker’s payload. These interactions would be considered involuntary and do not require that the user actively subvert protections built into the vulnerable system.
Vulnerable system confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the Vulnerable System.
Vulnerable system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 17 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade next.js and next to 16.1.7.

Affected software

Product	Affected	Fixed in
vercelnext.js	Affected >=16.0.1 <16.1.7	Fixed in 16.1.7
npmnext`pkg:npm/next`Other threats	Affected >=16.0.1 <16.1.7	Fixed in 16.1.7

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade Next.js to version 16.1.7 or later, where the vulnerability is fixed by proper origin validation.
Ensure that development servers running 'next dev' are not exposed to untrusted networks or the public internet. Restrict access to trusted internal networks only.
Configure network-level controls such as firewalls or reverse proxies to block WebSocket upgrade requests to '/_next/webpack-hmr' endpoints when the 'Origin' header is 'null'.
If immediate upgrade is not possible, implement strict access controls and monitoring on development servers to detect unauthorized WebSocket connections.
Educate developers about the risks of exposing development servers and enforce policies to avoid public exposure.
Review and configure the 'allowedDevOrigins' setting carefully to restrict allowed origins and prevent unauthorized connections.
Regularly audit development environments for exposure and apply security best practices to isolate development infrastructure from untrusted sources.

Description

CVE-2026-27977 is a low-severity vulnerability affecting development mode in Next.js versions 16.0.1 up to but not including 16.1.7. It involves missing origin validation in WebSocket connections used for Hot Module Replacement (HMR) during development. Specifically, the dev server's WebSocket endpoint could treat an 'Origin: null' header as a bypass, allowing attacker-controlled or sandboxed contexts to connect unexpectedly if the dev server is exposed to untrusted networks. This could enable an attacker to interact with development WebSocket traffic, potentially leaking sensitive information or manipulating the development environment. The issue is fixed in version 16.

Impact

The impact of CVE-2026-27977 is primarily limited to development environments using vulnerable versions of Next.js. If a development server is exposed to attacker-controlled content or untrusted networks, an attacker could connect to the internal HMR WebSocket channel by exploiting the missing origin validation. This could allow the attacker to observe or manipulate development-time WebSocket traffic, potentially leaking sensitive information such as source code, environment variables, or other development artifacts. However, since this vulnerability only affects development mode and not production deployments, the risk to live applications and end users is minimal. The vulnerability could disrupt the developer workflow or compromise the confidentiality of development data. Organizations that expose development servers publicly or do not restrict access to trusted networks are at higher risk. Overall, the impact is low for most organizations, but it could be more significant in environments where development servers are accessible externally or where sensitive data is handled during development.

CWE-1385Missing Origin Validation in WebSockets (opens in a new tab)
Variant weakness
The product uses a WebSocket, but it does not properly verify that the source of data or communication is valid.
Implementation
Enable CORS-like access restrictions by verifying the 'Origin' header during the WebSocket handshake.
Implementation
Use a randomized CSRF token to verify requests.
Implementation
Use TLS to securely communicate using 'wss' (WebSocket Secure) instead of 'ws'.
OWASP ASVS 4.0.3
V14.5.2 (opens in a new tab)
V14.5.3 (opens in a new tab)
V1.4.4 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Mar 2026, 01:01 UTC

WeaknessesCWE-1385

Technical details

References

Community reviews

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