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WasmtimeApplication · Bytecodealliance

CVE-2026-34983

MEDIUM · 5.0 CVSS v3.1 Published 2026-04-09
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
50/100
Remediation priority · Moderate

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. In 43.0.0, cloning a wasmtime::Linker is unsound and can result in use-after-free bugs. This bug is not controllable by guest Wasm programs. It can only be triggered by a specific sequence of embedder API calls made by the host. Specifically, the following steps must occur to trigger the bug clone a wasmtime::Linker, drop the original linker instance, use the new, cloned linker instance, resulting in a use-after-free. This vulnerability is fixed in 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

In Wasmtime 43.0.0, cloning a wasmtime::Linker creates a shallow copy that shares internal state with the original. When the original linker is dropped while the clone remains in use, the shared resources are freed, causing a use-after-free when the cloned linker is subsequently accessed. This is a memory safety bug triggered only through specific host-side API call sequences, not by guest Wasm code.

MitigationUpgrade Wasmtime to version 43.0.1 or later. If upgrading is not immediately feasible, audit code to avoid the pattern of cloning a Linker, dropping the original, then using the clone.

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:= 43.0.0

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
Local
Complexity
Low
Privileges
Low
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:R/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 Wasmtime version in use
    Check the installed Wasmtime library version by inspecting Cargo.toml dependencies, or run `cargo tree -p wasmtime` to list the exact version, or query the runtime via `wasmtime --version` if CLI is used
    Affected if The version is exactly 43.0.0
  2. Locate Linker usage in source code
    Search codebase for `wasmtime::Linker` type instantiation and look for `.clone()` calls on Linker instances
    Affected if Code contains patterns like `linker.clone()` where a Linker is cloned
  3. Determine drop order of original and clone
    Inspect code paths where the original Linker and its clone are used; trace lifetimes to see if the original is dropped (goes out of scope) while the clone is still referenced
    Affected if The original Linker is dropped (explicitly or via scope exit) before the cloned Linker is accessed again, creating a use-after-free condition

A user is affected if Wasmtime version 43.0.0 is in use AND their code clones a wasmtime::Linker and drops the original before using the clone.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Wasmtime to version 43.0.1 or later. If upgrading is not immediately feasible, audit code to avoid the pattern of cloning a Linker, dropping the original, then using the clone.

Recommended fix High confidence

43.0.1

  1. Upgrade Wasmtime from version 43.0.0 to version 43.0.1
  2. Verify the upgrade by checking the Wasmtime version
  3. Test the application to confirm the Linker cloning behavior now works correctly
  4. If using a package manager or dependency management system, update the dependency specification to require version 43.0.1 or later

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

Fix this in Wasmtime Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,190
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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-2026-34983 in production — separate from our analysis above.

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