dbcve.org
WasmtimeApplication · Bytecodealliance

CVE-2026-34943

HIGH · 7.5 CVSS v3.1 Published 2026-04-09
Fix available
A fix is available. Upgrade to 24.0.7 / 36.0.7 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. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime contains a possible panic which can happen when a flags-typed component model value is lifted with the Val type. If bits are set outside of the set of flags the component model specifies that these bits should be ignored but Wasmtime will panic when this value is lifted. This panic only affects wasmtime's implementation of lifting into Val, not when using the flags! macro. This additionally only affects flags-typed values which are part of a WIT interface. This has the risk of being a guest-controlled panic within the host which Wasmtime considers a DoS vector. 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 confidence

Wasmtime contains a guest-triggerable panic when lifting flags-typed component model values with extra bits set into the Val type. According to the component model spec, extra bits should be ignored, but Wasmtime instead panics. This only affects flags values in WIT interfaces when using the Val lifting API, not the flags! macro. A malicious guest can trigger this panic, causing denial of service on the host.

MitigationUpgrade Wasmtime to version 24.0.7, 36.0.7, 42.0.2, or 43.0.1 or later to resolve the panic condition.

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:< 24.0.7>= 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 Wasmtime installation and version
    Run `wasmtime --version` or check the Wasmtime library version in your dependency manifest (Cargo.toml, package.json, etc.)
    Affected if The installed version is < 24.0.7, or between 25.0.0 and 36.0.7, or between 37.0.0 and 42.0.2, or between 43.0.0 and 43.0.1
  2. Determine if component model with WIT interfaces is in use
    Inspect your Wasmtime runtime configuration and loaded modules for usage of the component model (check for `wasmtime::component::Val` or component imports with WIT files)
    Affected if You are using Wasmtime's component model feature with WIT-defined interfaces containing flags types
  3. Verify use of the Val lifting API
    Search your codebase or runtime configuration for calls to lift values into the Val type, such as `Val::from_*` methods or similar lifting functions applied to flags-typed data from WIT interfaces
    Affected if Your code uses the Val lifting API to convert flags-typed component model values from WIT interfaces (not the flags! macro)
  4. Confirm guest-controlled flags input
    Review whether untrusted WebAssembly guests can invoke functions accepting flags-typed arguments defined in WIT interfaces and pass arbitrary flag combinations
    Affected if Untrusted guest code can call exported functions that accept flags-typed parameters from WIT interfaces, allowing extra bits to be set

You are affected if your Wasmtime version falls within any of the vulnerable ranges AND you use the Val lifting API to handle flags-typed values from WIT interfaces with untrusted guest input.

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 24.0.7 / 36.0.7 / 42.0.2 or later
Fixed in 24.0.736.0.742.0.2
Interim mitigation

Upgrade Wasmtime to version 24.0.7, 36.0.7, 42.0.2, or 43.0.1 or later to resolve the panic condition.

Recommended fix High confidence

Wasmtime 24.0.7, 36.0.7, 42.0.2, or 43.0.1 (depending on your current major version branch)

  1. 1. Identify the current Wasmtime version in use by checking your Cargo.toml, lock file, or runtime configuration
  2. 2. Determine which major version branch you are on (24.x, 25.x-36.x, 37.x-42.x, or 43.x)
  3. 3. For 24.x branch: upgrade to version 24.0.7 or later
  4. 4. For 25.x-36.x branch: upgrade to version 36.0.7 or later
  5. 5. For 37.x-42.x branch: upgrade to version 42.0.2 or later
  6. 6. For 43.x branch: upgrade to version 43.0.1
  7. 7. Update the Wasmtime dependency in your Cargo.toml (e.g., change wasmtime = "24.0" to wasmtime = "24.0.7")
  8. 8. Run cargo update wasmtime to refresh the lock file
Caveat No breaking changes are mentioned in the advisory; this is a bug fix for a panic condition

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

Fix this in Wasmtime Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing4.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,540
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,464.

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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-2026-34943 in production — separate from our analysis above.

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What this is

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  • Version or environment caveats, and links to real fixes
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