MediumCVE-2026-128121

    Sveltejs Kit: Permissive Regular Expression (CVE-2026-128121)

    Published Last modified Sources: CVE.org, EUVD, OSV, Hersteller

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    What is affected, what to do

    SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. Prior to @sveltejs/adapter-vercel 6.3.5 and 7.0.2 and @sveltejs/adapter-static 3.0.11 and 4.0.1, an attacker-influenced link crawled during prerendering could be emitted into the generated Vercel routing configuration without escaping regular-expression metacharacters.

    Update Sveltejs Kit to version 2.70.4, @sveltejs Adapter-vercel to version 6.3.5, @sveltejs Adapter-static to version 3.0.11.

    Affected
    • Sveltejs Kit gte 3.0.0-next.0, < 3.1.1..*
    • Sveltejs Kit lt *..2.70.4
    • @sveltejs Adapter-vercel gte 7.0.0-next.0, < 7.0.2..*
    • @sveltejs Adapter-vercel lt *..6.3.5
    • @sveltejs Adapter-static gte 4.0.0-next.0, < 4.0.1..*
    • @sveltejs Adapter-static lt *..3.0.11
    Fixed in
    • Sveltejs Kit 2.70.4
    • @sveltejs Adapter-vercel 6.3.5
    • @sveltejs Adapter-static 3.0.11

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    5.9

    XIEM Effective CVSS

    Highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    5.9

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: CVE.org, EUVD, OSV, Hersteller

    —

    EPSS score

    No value is available for this vulnerability.

    Show all metrics
    Severity
    Medium
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    59.50 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    5.9 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    5.9
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 13 November 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-116, CWE-625

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. Prior to @sveltejs/adapter-vercel 6.3.5 and 7.0.2 and @sveltejs/adapter-static 3.0.11 and 4.0.1, an attacker-influenced link crawled during prerendering could be emitted into the generated Vercel routing configuration without escaping regular-expression metacharacters. The configuration could consequently interpret the path as regular-expression syntax, match unintended application paths, and expose content or behavior outside the intended path. This issue is fixed in @sveltejs/adapter-vercel 6.3.5 and 7.0.2 and @sveltejs/adapter-static 3.0.11 and 4.0.1.

    Source: cvelistv5, ENISA EUVD, NVD (NIST), OSV (Open Source Vulnerabilities), GitHub Security Advisories, CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    @sveltejsadapter-static
    • < 3.0.11
    • ≥ 4.0.0-next.0, < 4.0.1
    • 3.0.11
    • —
    @sveltejsadapter-vercel
    • ≥ 7.0.0-next.0, < 7.0.2
    • < 6.3.5
    • —
    • 6.3.5
    sveltejskit
    • < 2.70.4
    • ≥ 3.0.0-next.0, < 3.1.1
    • 2.70.4
    • —
    npm@sveltejs/adapter-static
    • 4.0.0-next.0
    • >= 4.0.0-next.0, < 4.0.1
    • < 3.0.11
    • —
    • 4.0.1
    • 4.0.1
    • 3.0.11
    • 3.0.11
    npm@sveltejs/adapter-vercel
    • —
    • < 6.3.5
    • 7.0.0-next.0
    • >= 7.0.0-next.0, < 7.0.2
    • 6.3.5
    • 6.3.5
    • 7.0.2
    • 7.0.2

    Vendors and products

    Weakness classes (CWE)

    • CWE-116Improper Encoding or Escaping of Output

      Class

      The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

      Entry at MITRE CWE-116

    • CWE-625Permissive Regular Expression

      Base

      The product uses a regular expression that does not sufficiently restrict the set of allowed values.

      Entry at MITRE CWE-625

    References & sources

    • github.comsveltejs/kit/commit/0a2e58cbccdd46cac20aa5af4e2edf17e0da11ddx_refsource_MISC, euvd, web
    • github.comsveltejs/kit/commit/2ed61a6aa3ac230b89e3528654c587847d1525a0x_refsource_MISC, euvd, web
    • github.comsveltejs/kit/pull/17620x_refsource_MISC, euvd, web
    • github.comsveltejs/kit/releases/tag/@sveltejs/adapter-static@3.0.11x_refsource_MISC, euvd, web
    • github.comsveltejs/kit/releases/tag/@sveltejs/adapter-static@4.0.1x_refsource_MISC, euvd, web
    • github.comsveltejs/kit/releases/tag/@sveltejs/adapter-vercel@6.3.5x_refsource_MISC, euvd, web
    • github.comsveltejs/kit/releases/tag/@sveltejs/adapter-vercel@7.0.2x_refsource_MISC, euvd, web
    • github.comsveltejs/kit/security/advisories/GHSA-jf9x-2fg2-hx4wx_refsource_CONFIRM, euvd, web
    • github.comsveltejs/kitpackage

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. ReceivedGitHub

      CVSS V3.1: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

      Weakness type: CWE-116, CWE-625

      Description added or changed

      Show 13 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. Prior to @sveltejs/adapter-vercel 6.3.5 and 7.0.2 and @sveltejs/adapter-static 3.0.11 and 4.0.1, an attacker-influenced link crawled during prerendering could be emitted into the generated Vercel routing configuration without escaping regular-expression metacharacters. The configuration could consequently interpret the path as regular-expression syntax, match unintended application paths, and expose content or behavior outside the intended path. This issue is fixed in @sveltejs/adapter-vercel 6.3.5 and 7.0.2 and @sveltejs/adapter-static 3.0.11 and 4.0.1.
      CVSSadded
      —
      AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
      Weakness type (CWE)added
      —
      CWE-116
      Weakness type (CWE)added
      —
      CWE-625
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/128xxx/CVE-2026-128121.json">CVE-2026-128121</a>
      Referenceadded
      —
      https://github.com/sveltejs/kit/commit/0a2e58cbccdd46cac20aa5af4e2edf17e0da11dd
      Referenceadded
      —
      https://github.com/sveltejs/kit/commit/2ed61a6aa3ac230b89e3528654c587847d1525a0
      Referenceadded
      —
      https://github.com/sveltejs/kit/pull/17620
      Referenceadded
      —
      https://github.com/sveltejs/kit/releases/tag/@sveltejs/adapter-static@3.0.11
      Referenceadded
      —
      https://github.com/sveltejs/kit/releases/tag/@sveltejs/adapter-static@4.0.1
      Referenceadded
      —
      https://github.com/sveltejs/kit/releases/tag/@sveltejs/adapter-vercel@6.3.5
      Referenceadded
      —
      https://github.com/sveltejs/kit/releases/tag/@sveltejs/adapter-vercel@7.0.2
      Referenceadded
      —
      https://github.com/sveltejs/kit/security/advisories/GHSA-jf9x-2fg2-hx4w

      Source identifier: security-advisories@github.com

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