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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

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.

How does O3 Security protect against CVE-2026-29057?

O3 pinpoints whether CVE-2026-29057 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

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 0.4%, placing it in the 34th 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.

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 April 10, 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.js: HTTP request smuggling in rewrites

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk34th percentile+0.40%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

2 pkgs affected

📦next📦next

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.

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	`next`	≥ 9.5.0&&< 15.5.13	15.5.13

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for next. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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.
How O3 protects you
O3 pinpoints whether CVE-2026-29057 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2026-29057. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

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

Is CVE-2026-29057 in your dependencies?

O3 detects CVE-2026-29057 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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CVE-2026-29057