Wasmtime has host data leakage with 64-bit tables and Winch

Impact Wasmtime's Winch compiler contains a bug where a 64-bit table, part of the memory64 proposal of WebAssembly, incorrectly translated the table.size instruction. This bug could lead to disclosing data on the host's stack to WebAssembly guests. The host's stack can possibly contain sensitive...

EUVD-2026-21023

Wasmtime segfault or unused out-of-sandbox load with f64x2.splat operator on x86-64...

Wasmtime segfault or unused out-of-sandbox load with `f64x2.splat` operator on x86-64

On x86-64 platforms with SSE3 disabled Wasmtime's compilation of the f64x2.splat WebAssembly instruction with Cranelift may load 8 more bytes than is necessary. When signals-based-traps are disabled this can result in a uncaught segfault due to loading from unmapped guard pages. With guard pages...

GHSA-QQFJ-4VCM-26HV Wasmtime segfault or unused out-of-sandbox load with `f64x2.splat` operator on x86-64

On x86-64 platforms with SSE3 disabled Wasmtime's compilation of the f64x2.splat WebAssembly instruction with Cranelift may load 8 more bytes than is necessary. When signals-based-traps are disabled this can result in a uncaught segfault due to loading from unmapped guard pages. With guard pages...

EUVD-2026-21022

Wasmtime has a possible panic when lifting flags component value...

GHSA-M758-WJHJ-P3JQ Wasmtime has a possible panic when lifting `flags` component value

Impact 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 pani...

Wasmtime has a possible panic when lifting `flags` component value

Impact 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 pani...

Wasmtime: Panic when transcoding misaligned utf-16 strings

Impact Wasmtime's implementation of transcoding strings into the Component Model's utf16 or latin1+utf16 encodings improperly verified the alignment of reallocated strings. This meant that unaligned pointers could be passed to the host for transcoding which would trigger a host panic. This panic ...

GHSA-JXHV-7H78-9775 Wasmtime: Panic when transcoding misaligned utf-16 strings

Impact Wasmtime's implementation of transcoding strings into the Component Model's utf16 or latin1+utf16 encodings improperly verified the alignment of reallocated strings. This meant that unaligned pointers could be passed to the host for transcoding which would trigger a host panic. This panic ...

EUVD-2026-20990

Wasmtime: Panic when transcoding misaligned utf-16 strings...

EUVD-2026-20988

Wasmtime: Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding...

GHSA-HX6P-XPX3-JVVV Wasmtime: Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding

Summary 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...

Wasmtime: Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding

Summary 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...

CVE-2026-34987

Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime with its Winch baseline non-default compiler backend may allow properly constructed guest Wasm to access host memory outside of its linear-memory sandbox. This vulnerability requires use of the Winch...

DEBIAN-CVE-2026-35186

Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Winch compiler backend contains a bug where translating the table.grow operator causes the result to be incorrectly typed. For 32-bit tables this means that the result of the operator, internally i...

CVE-2026-34988

Wasmtime is a runtime for WebAssembly. From 28.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's implementation of its pooling allocator contains a bug where in certain configurations the contents of linear memory can be leaked from one instance to the next. The implementation of resetting the...

DEBIAN-CVE-2026-34988

Wasmtime is a runtime for WebAssembly. From 28.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's implementation of its pooling allocator contains a bug where in certain configurations the contents of linear memory can be leaked from one instance to the next. The implementation of resetting the...

DEBIAN-CVE-2026-34987

Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime with its Winch baseline non-default compiler backend may allow properly constructed guest Wasm to access host memory outside of its linear-memory sandbox. This vulnerability requires use of the Winch...

DEBIAN-CVE-2026-35195

Wasmtime 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...

CVE-2026-35195

Wasmtime 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...