dbcve.org
WasmtimeApplication · Bytecodealliance

CVE-2026-34946

HIGH · 7.5 CVSS v3.1 Published 2026-04-09
Fix available
A fix is available. Upgrade to 36.0.7 / 42.0.2 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Winch compiler contains a vulnerability where the compilation of the table.fill instruction can result in a host panic. This means that a valid guest can be compiled with Winch, on any architecture, and cause the host to panic. This represents a denial-of-service vulnerability in Wasmtime due to guests being able to trigger a panic. The specific issue is that a historical refactoring changed how compiled code referenced tables within the table.* instructions. This refactoring forgot to update the Winch code paths associated as well, meaning that Winch was using the wrong indexing scheme. Due to the feature support of Winch the only problem that can result is tables being mixed up or nonexistent tables being used, meaning that the guest is limited to panicking the host (using a nonexistent table), or executing spec-incorrect behavior and modifying the wrong table. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The Winch compiler in Wasmtime contains a vulnerability in handling the table.fill instruction where a historical code refactoring incorrectly updated table indexing. This causes the compiler to use wrong indexing schemes, allowing a valid guest WebAssembly module to either panic the host by accessing a nonexistent table or modify the wrong table, resulting in a denial-of-service vulnerability.

MitigationUpgrade Wasmtime to version 36.0.7, 42.0.2, or 43.0.1 or later to receive the patch for this vulnerability.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
WasmtimeApplication
Affected:>= 25.0.0, < 36.0.7>= 37.0.0, < 42.0.2>= 43.0.0, < 43.0.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Wasmtime version
    Run 'wasmtime --version' from command line, or check the version in your project dependencies (Cargo.toml, package.json, etc.)
    Affected if version is 25.0.0 through 36.0.6, 37.0.0 through 42.0.1, or 43.0.0 exactly
  2. Determine if Winch compiler is enabled
    Check your Wasmtime configuration or runtime settings for whether Winch (the baseline compiler) is selected. Default Wasmtime uses Cranelift; look for explicit winch configuration in your runtime setup.
    Affected if Winch compiler is explicitly configured as the WebAssembly compiler backend
  3. Confirm WebAssembly module uses tables
    Inspect the WebAssembly module with a tool like wasm-objdump or wasm2wat to check for table definitions or table.fill, table.get, table.set instructions in the module.
    Affected if The module contains table definitions or uses the table.fill instruction

You are affected if you are running an affected Wasmtime version (25.0.0-36.0.6, 37.0.0-42.0.1, or 43.0.0) with the Winch compiler enabled and your WebAssembly workload uses tables with the table.fill instruction.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 36.0.7 / 42.0.2 / 43.0.1 or later
Fixed in 36.0.742.0.243.0.1
Interim mitigation

Upgrade Wasmtime to version 36.0.7, 42.0.2, or 43.0.1 or later to receive the patch for this vulnerability.

Recommended fix High confidence

Upgrade to Wasmtime 36.0.7, 42.0.2, or 43.0.1 (whichever is the nearest stable release above your current version)

  1. Identify the current Wasmtime version in use by checking Cargo.toml or the project's dependency lock file
  2. Determine which affected version range your current version falls into (25.0.0-36.x, 37.0.0-42.x, or 43.0.x)
  3. Update the Wasmtime dependency in Cargo.toml to the appropriate fixed version: 36.0.7 for versions in range >=25.0.0 <36.0.7, 42.0.2 for versions in range >=37.0.0 <42.0.2, or 43.0.1 for versions in range >=43.0.0 <43.0.1
  4. Run cargo update to update the lock file
  5. Rebuild the project with cargo build to ensure the new version is used
  6. Test the application to verify functionality remains intact
Caveat Review the Wasmtime release notes between your current version and the target upgrade version for any potential breaking changes in WebAssembly feature support or API changes

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Wasmtime Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,720
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-34946 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data