CriticalCVE-2026-115889

    Wasmtime: Bit-packing in Cranelift compiler causes silent overflow and miscompilation (CVE-2026-115889)

    Published Last modified Sources: pwn.watch, Msrc Update Guide, CVE.org, OSV, Hersteller

    What is affected, what to do

    Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values.

    Update Bytecode Alliance wasmtime to version 36.0.19.

    Affected
    • Bytecode Alliance wasmtime gte 37.0.0, < 43.0.0..*
    • Bytecode Alliance wasmtime lt *..36.0.19
    Fixed in
    • Bytecode Alliance wasmtime 36.0.19

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

    Metrics

    9.9

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    9.9

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: pwn.watch, Msrc Update Guide, CVE.org, OSV, Hersteller

    0.4 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 39.3

    Show all metrics
    Severity
    Critical
    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
    91.86 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
    9.9 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
    9.9
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.4 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    39.3
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    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: total
    Source: CISA Vulnrichment, as of 26 October 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-197, CWE-843

    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
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    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

    Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.

    Source: pwn.watch, Microsoft Security Update Guide, cvelistv5, NVD (NIST), OSV (Open Source Vulnerabilities), CVE.org (MITRE), GitHub Security Advisories

    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
    bytecodealliancewasmtime
    • ≥ 37.0.0, < 43.0.0
    • < 36.0.19
    • —
    • 36.0.19
    crates.iowasmtime
    • 37.0.0
    • 0.0.0-0
    • —
    • 43.0.0
    • 36.0.19
    • 36.0.19
    rustwasmtime
    • < 36.0.19
    • >= 37.0.0, < 43.0.0
    • 36.0.19
    • 43.0.0

    Vendors and products

    Weakness classes (CWE)

    • CWE-197Numeric Truncation Error

      Base

      Truncation errors occur when a primitive is cast to a primitive of a smaller size and data is lost in the conversion.

      Entry at MITRE CWE-197

    • CWE-843Access of Resource Using Incompatible Type ('Type Confusion')

      Base

      The product allocates or initializes a resource such as a pointer, object, or variable using one type, but it later accesses that resource using a type that is incompatible with the original type.

      Entry at MITRE CWE-843

    References & sources

    • github.combytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fm…x_refsource_CONFIRM, web, pwn-watch
    • github.combytecodealliance/wasmtime/pull/12613x_refsource_MISC, web
    • github.combytecodealliance/wasmtime/pull/14818x_refsource_MISC, web
    • github.combytecodealliance/wasmtime/commit/ba8f7d70caa1825b7f64fa75cd9d03…x_refsource_MISC, web
    • github.combytecodealliance/wasmtime/commit/f517bd6e890c7c1291ab9fe05d8cc0…x_refsource_MISC, web
    • github.combytecodealliance/wasmtime/releases/tag/v36.0.19x_refsource_MISC, web
    • github.combytecodealliance/wasmtime/releases/tag/v43.0.0x_refsource_MISC, web
    • github.combytecodealliance/wasmtimepackage
    • rustsec.orgadvisories/RUSTSEC-2026-0380.htmlweb, advisory
    • crates.iocrates/wasmtimepackage
    • pwn.watchpwn.watch: Wasmtime: two critical Cranelift miscompilation bugs let a malicious WebAssembly module escape the sandbox (CVE-2026-115889, CVE-2026-115893)pwn-watch
    • github.comGHSA-mghf-wjfp-p5xm: Cranelift backend on aarch64 can jump to incorrect target on large Wasm br_table instructionpwn-watch
    • thehackernews.comTwo Critical Wasmtime Flaws Could Let Malicious WebAssembly Modules Escape Sandboxespwn-watch

    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. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-115889","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-10-26T15:40:36.390562Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. ReceivedGitHub

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

      Weakness type: CWE-197, CWE-843

      Description added or changed

      Show 12 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      Wasmtime is a runtime for WebAssembly. Prior to 36.0.19 and 43.0.0, the Cranelift compiler backend bit-packs SSA value indices in a way that can silently overflow in release builds when compiling a sufficiently large or specially crafted Wasm function with many SSA values. The overflow can make Cranelift reference incorrect IR values, causing arbitrary miscompilation, type confusion, and other attacker-controlled effects that may escape the Wasm sandbox on any architecture using the default Cranelift backend. This issue is fixed in versions 36.0.19 and 43.0.0.
      CVSSadded
      —
      AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
      Weakness type (CWE)added
      —
      CWE-197
      Weakness type (CWE)added
      —
      CWE-843
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/115xxx/CVE-2026-115889.json">CVE-2026-115889</a>
      Referenceadded
      —
      https://github.com/bytecodealliance/wasmtime/commit/ba8f7d70caa1825b7f64fa75cd9d03f4a438dae0
      Referenceadded
      —
      https://github.com/bytecodealliance/wasmtime/commit/f517bd6e890c7c1291ab9fe05d8cc0c9f11e56aa
      Referenceadded
      —
      https://github.com/bytecodealliance/wasmtime/pull/12613
      Referenceadded
      —
      https://github.com/bytecodealliance/wasmtime/pull/14818
      Referenceadded
      —
      https://github.com/bytecodealliance/wasmtime/releases/tag/v36.0.19
      Referenceadded
      —
      https://github.com/bytecodealliance/wasmtime/releases/tag/v43.0.0
      Referenceadded
      —
      https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-897f-g5gm-fmxm

      Source identifier: security-advisories@github.com

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