WasmtimeApplication · Bytecodealliance
CVE-2026-34942
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 · uneditedWasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime's implementation of transcoding strings into the Component Model's utf16 or latin1+utf16 encodings improperly verified the alignment of reallocated strings. This meant that unaligned pointers could be passed to the host for transcoding which would trigger a host panic. This panic is possible to trigger from malicious guests which transfer very specific strings across components with specific addresses. Host panics are considered a DoS vector in Wasmtime as the panic conditions are controlled by the guest in this situation. This vulnerability is fixed in 24.0.7, 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 confidenceWasmtime's Component Model string transcoding implementation (utf16 and latin1+utf16 encodings) fails to properly verify alignment of reallocated strings. Malicious WebAssembly guests can transfer specially crafted strings with specific unaligned addresses across components, causing the host to panic. This is a denial-of-service vector since the guest controls the panic conditions.
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
< 24.0.7>= 25.0.0, < 36.0.7>= 37.0.0, < 42.0.2>= 43.0.0, < 43.0.1CVSS 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
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/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 checksWork through these to decide whether this CVE applies to you.
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Check installed Wasmtime versionRun `wasmtime --version` or inspect the Wasmtime library/binary version metadataAffected if The version is lower than 24.0.7, or falls between 25.0.0-36.0.6, 37.0.0-42.2.1, or 43.0.0-43.0.1
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Verify Wasmtime was compiled with Component Model supportCheck if the Wasmtime binary/library includes component model support (typically enabled by default in affected versions; confirm via `wasmtime --help` or runtime feature detection)Affected if Component Model support is present in the Wasmtime build
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Identify WebAssembly components using string imports/exports with utf16 or latin1+utf16 encodingsInspect the Wasm components loaded by Wasmtime for use of the Component Model with string types; examine the component's wit/wasm binary for encoding=utf16 or encoding=latin1+utf16 in string parameter typesAffected if Any loaded Wasm component uses utf16 or latin1+utf16 string encoding in its interface with the host
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Monitor for panics related to string alignment during component string transfersReview Wasmtime runtime logs or stderr for panic messages containing 'string' and 'alignment' keywords that occur during cross-component string passingAffected if Panics occur during component model string operations involving utf16 or latin1+utf16 encoded strings
You are affected if Wasmtime version is within the vulnerable ranges AND your workload loads WebAssembly components that use the Component Model with utf16 or latin1+utf16 string encodings.
Generated from the published advisory. Verify against your own configuration.
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 · scoped24.0.736.0.742.0.2
Upgrade Wasmtime to version 24.0.7, 36.0.7, 42.0.2, or 43.0.1 (or later) to obtain the patched runtime that properly validates string alignment before transcoding.
Upgrade to Wasmtime 24.0.7, 36.0.7, 42.0.2, or 43.0.1 (choose the version appropriate for your major version branch)
- 1. Identify the currently installed Wasmtime version using cargo list wasmtime or the project's dependency management system.
- 2. Determine which version branch (24.x, 36.x, 42.x, or 43.x) is appropriate for your project based on compatibility requirements.
- 3. Upgrade Wasmtime to the latest patch version in your chosen branch: 24.0.7, 36.0.7, 42.0.2, or 43.0.1.
- 4. For Cargo projects, update the Cargo.toml dependency: wasmtime = "X.Y.Z" where X.Y.Z is the chosen fixed version, then run cargo update wasmtime.
- 5. Rebuild and test the application in a non-production environment to verify the fix resolves the issue.
- 6. Deploy the updated version to production after successful testing.
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Wasmtime
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing12.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,616.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-34942 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-34942 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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