WasmtimeApplication · Bytecodealliance
CVE-2026-34941
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 contains a vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units. This vulnerability can cause the host to read beyond the end of a WebAssembly's linear memory in an attempt to transcode nonexistent bytes. In Wasmtime's default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16. A host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled. 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 contains an out-of-bounds read vulnerability in its UTF-16 to latin1+utf16 transcoding logic. The bounds check incorrectly validates the number of UTF-16 code units instead of the actual byte length, causing the runtime to read beyond the end of WebAssembly linear memory. In default configurations this hits guard pages causing a segfault (DoS); with guard pages disabled, this can read arbitrary host memory.
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
- High
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/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` from the command line, or inspect the Cargo.toml/dependency lock file if Wasmtime is embedded as a libraryAffected if The version is less than 24.0.7, or falls between 25.0.0 and 36.0.6, or between 37.0.0 and 42.0.1, or between 43.0.0 and 43.0.1
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Check if guard pages are disabled in Wasmtime configurationInspect the Wasmtime configuration code or command-line flags for ` memory_guard: false` or equivalent setting that disables memory guardsAffected if Guard pages are disabled (makes the vulnerability more severe, allowing potential arbitrary host memory read)
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Identify if untrusted WASM modules are processedReview logs, execution environment, or application code to determine if Wasmtime loads WASM modules from untrusted or external sourcesAffected if Untrusted WASM modules are processed and the transcoding feature is exercised (the vulnerable code path)
You are affected if your Wasmtime version is within any of the vulnerable ranges AND your environment executes WASM modules that trigger the UTF-16 to latin1+utf16 transcoding logic.
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 patch the transcoding bounds check vulnerability.
Upgrade to 43.0.1 (or the appropriate fixed version for your branch: 24.0.7, 36.0.7, 42.0.2, or 43.0.1)
- 1. Identify the currently installed Wasmtime version using `wasmtime --version` or checking your dependency manager
- 2. Based on your current version, determine the appropriate upgrade target: for versions <24.0.7 upgrade to 24.0.7; for versions 25.x-36.x upgrade to 36.0.7; for versions 37.x-42.x upgrade to 42.0.2; for version 43.0.0 upgrade to 43.0.1
- 3. Upgrade Wasmtime using your package manager or by downloading the release from the official GitHub releases page (github.com/bytecodealliance/wasmtime/releases)
- 4. Verify the upgrade was successful by running `wasmtime --version` and confirming the version matches the expected fixed release
- 5. Test your WebAssembly workloads to ensure functionality is maintained after the upgrade
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 / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,464.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-34941 — 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-2026-34941 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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