Medium

Out-of-bounds write in Wasmtime component model string transcoding

IdentifiersCVE-2026-35195CWE-787· Out-of-bounds Write

CVE-2026-35195 is an out-of-bounds write vulnerability in Wasmtime’s implementation of string transcoding for the WebAssembly Component Model, specifically within the Fast Assembly Component Trampolines (FACT) compiler subsystem. During host/guest component string transfers, Wasmtime may call a guest component’s exported realloc function to obtain a destination buffer. In affected versions prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, the runtime does not properly validate the offset returned by the guest realloc before using it as the destination for transcoded string bytes. A malicious guest can therefore return an arbitrary 32-bit offset, causing the host runtime to compute an invalid destination address and write data to an arbitrary location up to 4 GiB away from the base of the guest linear memory. Depending on memory reservation and guard-page configuration, this results either in a host fault and process abort or corruption of memory outside the intended guest linear memory region, including host data structures or other guests’ linear memories.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

The primary impact is host-side out-of-bounds memory write during component string transcoding. In Wasmtime’s default configuration, where 4 GiB of virtual address space is reserved for guest linear memory with guard pages, exploitation will typically cause the host process to access unmapped memory and terminate, resulting in denial of service. In less protected configurations—such as reduced linear-memory reservation or disabled guard pages—the same flaw can corrupt memory outside the guest’s linear memory, potentially affecting host runtime data structures or adjacent guests’ memories. The provided content does not confirm reliable code execution, so the verified impacts are denial of service and memory corruption.

Mitigation

If you can’t patch tonight, do this now.

No workaround is identified in the provided content. If immediate upgrade is not possible, risk may be reduced by avoiding execution of untrusted guest components that use the WebAssembly Component Model string transcoding path, but the authoritative remediation is to upgrade to a patched Wasmtime version. The advisory states there is no known workaround.

Remediation

Patch, then assume compromise.

Upgrade Wasmtime to a fixed release. The vulnerability is fixed in versions 24.0.7, 36.0.7, 42.0.2, and 43.0.1. Deploy the appropriate patched version for the release branch in use.

PUBLIC EXPLOITS

Exploits

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VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

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VendorProductType

Bytecode AllianceWasmtimeapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

1 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

1 SOURCESView more in app

cvereportsNews

Apr 9, 2026

CVE-2026-35195: CVE-2026-35195: Out-of-Bounds Write in Wasmtime Component Model Transcoding | CVEReports

An out-of-bounds write vulnerability in Wasmtime's Fast Assembly Component Trampolines (FACT) compiler subsystem caused by improper validation of a guest-controlled realloc offset during string transcoding, leading to denial of service and potentially host memory corruption in certain configurations.

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Exposure mapping

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Threat actor evidence

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Associated malware

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Detection signatures

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Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity