WasmtimeApplication · Bytecodealliance
CVE-2026-35195
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 between components contains a bug where the return value of a guest component's realloc is not validated before the host attempts to write through the pointer. This enables a guest to cause the host to write arbitrary transcoded string bytes to an arbitrary location up to 4GiB away from the base of linear memory. These writes on the host could hit unmapped memory or could corrupt host data structures depending on Wasmtime's configuration. Wasmtime by default reserves 4GiB of virtual memory for a guest's linear memory meaning that this bug will by default on hosts cause the host to hit unmapped memory and abort the process due to an unhandled fault. Wasmtime can be configured, however, to reserve less memory for a guest and to remove all guard pages, so some configurations of Wasmtime may lead to corruption of data outside of a guest's linear memory, such as host data structures or other guests's linear memories. 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 string transcoding between components fails to validate the guest component's realloc return value before the host writes through the pointer. This allows a malicious guest to cause the host to write transcoded string bytes to arbitrary memory locations up to 4GiB beyond linear memory base, potentially corrupting host data structures or other guests' memories when guard pages are removed or memory is configured smaller than default.
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= 43.0.0CVSS 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
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
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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Determine Wasmtime versionRun `wasmtime --version` from command line, or call `wasmtime::Engine::wasmtime_version()` if using the Rust API, or check the Wasmtime library binary/dynamic library version metadataAffected if The version falls in any of these ranges: < 24.0.7, 25.0.0 to < 36.0.7, 37.0.0 to < 42.0.2, or exactly 43.0.0
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Verify if component model is enabledInspect the Wasmtime configuration: in Rust API check if `wasmtime::Config::wasm_component_model(true)` was called; in embedding check if components are being loaded via component model bindingsAffected if Component model is enabled and guest components that use string transcoding between components can be executed
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Inspect memory configuration for guard pagesCheck Wasmtime memory settings: in Rust API examine `wasmtime::Config::memory_guard_pages()` (default is true); in embedding configuration look for `--disable-memory-guard-pages` or equivalent settingAffected if Guard pages are disabled via configuration (memory_guard_pages set to false)
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Inspect custom memory size limitsCheck for custom linear memory limits: in Rust API examine `wasmtime::Config::max_memory_size()` or memory64 limits; in embedding look for custom memory allocation sizes smaller than defaultAffected if Memory is configured smaller than default (for example, via max_memory_size with a value reducing the addressable range)
You are affected if your Wasmtime version is in the vulnerable list AND component model is enabled AND (guard pages are disabled OR custom memory limits reduce the default guard region).
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. If immediate upgrade is not feasible, verify that guard pages are enabled and default memory allocation is retained to limit impact to process abort rather than memory corruption.
Wasmtime 24.0.7, 36.0.7, 42.0.2, or 43.0.1 (depending on which major version branch you are on)
- 1. Identify the currently installed Wasmtime version using `wasmtime --version` or checking your dependency lock file
- 2. Based on your current version, upgrade to the corresponding fixed release: if version < 24.0.7, upgrade to 24.0.7; if version >= 25.0.0 and < 36.0.7, upgrade to 36.0.7; if version >= 37.0.0 and < 42.0.2, upgrade to 42.0.2; if version == 43.0.0, upgrade to 43.0.1
- 3. If using Cargo, update the Cargo.toml dependency: `cargo update -p wasmtime` or specify the version directly
- 4. If using a pre-built binary, download the new release from github.com/bytecodealliance/wasmtime/releases
- 5. Rebuild and redeploy your application with the updated Wasmtime dependency
- 6. Verify the new version is active with `wasmtime --version`
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-2026-35195 — 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-2026-35195 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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