VulnerabilityPublished 18 Mar 2026

CVE-2026-29057: vercel next.js · HTTP Request/Response Smuggling

Affects vercel next.jsSource CVE Database V5

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Not known to be exploited · CVSS 6.3 Medium : upgrade to 16.1.7 or 15.5.13 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score

6.3Medium

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 39% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 16.1.7, 15.5.13

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/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: None
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: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
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 18 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
Public exploit code: GitHub proofs of concept
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), GitHub proofs of concept, 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 vercel/next.js to 16.1.7 or 15.5.13.

Affected software

Product	Affected	Fixed in
vercelnext.js	Affected >=16.0.0-beta.0 <16.1.7	Fixed in 16.1.7
vercelnext.js	Affected >=9.5.0 <15.5.13	Fixed in 15.5.13
GitHubvercel/next.js`pkg:github/vercel/next.js`Other threats	Affected <15.5.13 <16.1.7	Fixed in 15.5.13 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 15.5.13 or later, or 16.1.7 or later, which include the fix for this vulnerability by correcting the handling of content-length and transfer-encoding headers during proxy rewrites.
If upgrading is not immediately possible, implement edge or proxy-level controls to block HTTP DELETE and OPTIONS requests that use Transfer-Encoding: chunked on rewritten routes to prevent smuggling attempts.
Enforce strict authentication and authorization on all backend routes, especially internal and administrative endpoints, to limit access even if request smuggling occurs.
Conduct thorough security testing, including HTTP request smuggling tests, on applications using Next.js proxy rewrites to detect potential exploitation paths.
Monitor web server and application logs for anomalous or malformed HTTP requests indicative of request smuggling attempts.
Consider deploying Web Application Firewalls (WAFs) with rules specifically designed to detect and block HTTP request smuggling techniques.
For deployments on cloud or CDN providers, verify that rewrites are handled at the CDN or edge level, which mitigates this vulnerability inherently.
Educate development and operations teams about the risks of HTTP request smuggling and secure proxy configuration best practices to prevent similar issues.

Description

Next.js is a React framework for building full-stack web applications. Starting in version 9.5.0 and prior to versions 15.5.13 and 16.1.7, when Next.js rewrites proxy traffic to an external backend, a crafted `DELETE`/`OPTIONS` request using `Transfer-Encoding: chunked` could trigger request boundary disagreement between the proxy and backend. This could allow request smuggling through rewritten routes. An attacker could smuggle a second request to unintended backend routes (for example, internal/admin endpoints), bypassing assumptions that only the configured rewrite destination/path is reachable. This does not impact applications hosted on providers that handle rewrites at the CDN level, such as Vercel. The vulnerability originated in an upstream library vendored by Next.js. It is fixed in Next.js 15.5.13 and 16.1.7 by updating that dependency’s behavior so `content-length: 0` is added only when both `content-length` and `transfer-encoding` are absent, and `transfer-encoding` is no longer removed in that code path. If upgrading is not immediately possible, block chunked `DELETE`/`OPTIONS` requests on rewritten routes at the edge/proxy, and/or enforce authentication/authorization on backend routes.

Impact

This vulnerability allows attackers to bypass route restrictions by smuggling additional HTTP requests to backend endpoints that are not intended to be accessible via the rewritten routes. This can lead to unauthorized access to sensitive internal or administrative interfaces, potentially exposing confidential data or enabling further exploitation. The inconsistent interpretation of HTTP requests between proxy and backend can undermine application security assumptions, leading to integrity violations and partial confidentiality breaches. Since the attack requires no authentication or user interaction and can be executed remotely over the network, the attack surface is broad for affected Next.js applications that perform proxy rewrites. Organizations using vulnerable Next.js versions in their web applications risk unauthorized access, data leakage, and potential compromise of backend services. However, applications hosted on providers that handle rewrites at the CDN level, such as Vercel, are not affected, reducing risk for those deployments. The absence of known active exploits reduces immediate risk but does not eliminate the threat, especially as exploit techniques for HTTP request smuggling are well understood and can be weaponized.

CWE-444Inconsistent Interpretation of HTTP Requests (HTTP Request Smuggling) (opens in a new tab)
Base weaknessOWASP Top 10 A06:2025: Insecure Design (opens in a new tab)
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
Implementation
Use a web server that employs a strict HTTP parsing procedure, such as Apache.
Implementation
Use only SSL communication.
Implementation
Terminate the client session after each request.
OWASP Cheat Sheets
REST Assessment (opens in a new tab)
REST Security (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
Secure Design Principles (opens in a new tab)
OWASP ASVS 4.0.3
V13.2.5 (opens in a new tab)
Attack patterns
HTTP Response Smuggling (opens in a new tab)
HTTP Request Smuggling (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 18 Mar 2026, 01:13 UTC

Public exploits and detectionGitHub proofs of concept

WeaknessesCWE-444

Technical details

References

Community reviews

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