How severe is CVE-2026-29057?

No CVSS score has been assigned to CVE-2026-29057 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-29057?

CVE-2026-29057 affects the following packages: next (npm), next (npm). Ecosystems affected: npm.

How do I fix CVE-2026-29057?

Update next to 16.1.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-29057 is resolved across your whole dependency graph.

How do I detect CVE-2026-29057 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-2026-29057 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-2026-29057 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-29057 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-2026-29057?

CVE-2026-29057 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 40th 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-2026-29057?

CVE-2026-29057 is classified as CWE-444 (CWE-444). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-29057 published, and has it been updated?

CVE-2026-29057 was published on March 18, 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.

CVE-2026-29057: next — Fixed in 16.1.7

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
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-2026-29057.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk+0.01%

Lower risk than most CVEs40th percentile — riskier than 40% of all scored CVEsHighest risk

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

Real-World Exposure

2 pkgs 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

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.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`next`	≥ 16.0.0-beta.0&&< 16.1.7	16.1.7`npm install next@16.1.7`
📦npm	`next`	≥ 9.5.0&&< 15.5.13	15.5.13`npm install next@15.5.13`

Affected Products

1 product · 2 configurations

Application

next.jsvercel

≥ 16.0.0 && < 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-2026-29057 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-2026-29057 (CC BY 4.0)

Frequently Asked Questions

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 reach

O3 Security · Impact-Aware SCA

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CVE-2026-29057 — next