CVE-2026-126406

Wasmtime before 36.0.20 HTTP Request Smuggling via wasi-http p2 Content-Length

The wasmtime-wasi-http p2 implementation in Wasmtime before 36.0.20, 37.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 can send conflicting content-length headers, or ones not matching the body, in outgoing requests. A guest that reuses a received response's headers resource to send a bodyless request can enable request smuggling against non-compliant servers, potentially bypassing embedder destination access controls.

CVSS 4.0 · 6.3 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-126407

Wasmtime before 36.0.20 Denial of Service via Borrowed Resource Transfer

Wasmtime before 36.0.20, 37.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 allocates untracked host memory when a component receives a borrow of a resource it defines itself, bypassing the per-store handle limit. A malicious guest component can repeatedly transfer such borrowed resources to consume arbitrary host memory, causing denial of service.

CVSS 4.0 · 5.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-126408

Wasmtime 47.0.0 before 48.0.8 Denial of Service via TypedFunc Type-Check Panic

Wasmtime 47.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 contains an insufficient type-check in the TypedFunc embedder API for I31, Option<I31>, and Option<NoneRef> parameter or result types, reaching an unreachable!() path. A malicious guest module exporting a function that uses another anyref-hierarchy type can panic the host embedding, causing denial of service.

CVSS 4.0 · 1 Low EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-126409

Wasmtime 47.0.0 before 48.0.8 Cross-Engine Type Confusion via StructType Supertype

Wasmtime 47.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 contains a cross-engine type confusion vulnerability because StructType::with_finality_and_supertype does not validate that the supplied supertype belongs to the same Engine. Embedders using multiple engines that create a GC struct type with another engine's supertype can trigger runtime panics or GC heap corruption, causing denial of service; guest WebAssembly cannot trigger it.

CVSS 4.0 · 1.8 Low EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-126410

Wasmtime 48.0.0 before 48.0.8 TOCTOU UDP Send Policy Bypass via wasip3 Sockets

Wasmtime's wasmtime-wasi crate 48.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 contains a time-of-check/time-of-use race in the wasip3 wasi:sockets udp-socket host implementation that lets guests bypass socket_addr_check send restrictions. A malicious guest can race udp-socket.send against udp-socket.connect to deliver attacker-controlled datagrams to addresses the policy permits only for receiving.

CVSS 4.0 · 5.3 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-121439

Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 HTTP Response Splitting via wasi-http

Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 contains a response splitting vulnerability in wasi-http p3 that allows guests to set unvalidated content-length headers. Malicious wasip3 guests can splice an existing body into a new response with an incorrect content-length to perform response splitting or injection attacks.

CVSS 4.0 · 6.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-115391

Wasmtime 46.0.0 before 46.0.3 and 47.0.0 before 47.0.4 Unbounded Heap Allocation via WASIp3 Streams

Wasmtime 46.0.0 before 46.0.3 and 47.0.0 before 47.0.4 contains an uncontrolled resource allocation vulnerability in its WASIp3 implementation that buffers guest-specified-length writes on the host without limit. Malicious guests can offer large buffers to WASIp3 file or HTTP write streams, causing the host to copy and buffer all bytes, bounded only by guest linear memory, exhausting host memory.

CVSS 4.0 · 6.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-118688

Wasmtime before 36.0.18, 37.0.0 before 48.0.6, and 49.0.0 before 49.0.3 Sandbox Escape via Symlink Rename

wasmtime-wasi in Wasmtime before 36.0.18, 37.0.0 before 48.0.6, and 49.0.0 before 49.0.3 re-appends a trailing slash to rename source paths, causing renameat on macOS and FreeBSD hosts to follow directory symlinks. A guest with sandbox write access can rename a relative symlink such as "up/" to move host directories into its sandbox and read or write them.

CVSS 4.0 · 8.8 High EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-115387

Wasmtime before 36.0.16, 37.0.0 before 48.0.3, and 49.0.0 before 49.0.1 Host Panic via WASI Filesystem Timestamp Overflow

Wasmtime before 36.0.16, 37.0.0 before 48.0.3, and 49.0.0 before 49.0.1 contains a denial of service vulnerability in wasmtime-wasi that allows guest WASI programs to panic the host via overflowing filesystem timestamps. Attackers can pass atim or mtim values whose sub-second field overflows the seconds field to path_filestat_set_times, fd_filestat_set_times, set-times, or set-times-at, crashing the host.

CVSS 4.0 · 6.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-115383

Wasmtime 47.0.0 before 48.0.4 and 49.0.0 before 49.0.2 GC Heap Corruption via Tag Imports

Wasmtime 47.0.0 before 48.0.4 and 49.0.0 before 49.0.2 contains an improper validation vulnerability that accepts components whose core modules import WebAssembly tags with a subtype of the original type. Malicious guests can mis-type exception object payloads to corrupt the GC heap, causing Wasmtime to panic when the exceptions proposal is enabled.

CVSS 4.0 · 5.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-115379

Wasmtime 47.0.0 before 48.0.4 and 49.0.0 before 49.0.2 GC Heap Corruption via try_call

Wasmtime 47.0.0 before 48.0.4 and 49.0.0 before 49.0.2 contains a missing GC rooting vulnerability that leaves references live across try_call unrooted when compiling Wasm modules. Attackers can supply Wasm modules whose callee triggers garbage collection, leaving stale or dangling references that cause GC heap corruption or incorrect execution.

CVSS 4.0 · 6.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-119143

Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 Panic via Zero-Length Stream Writes

Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a denial of service vulnerability that allows guest code to trigger a host panic through out-of-bounds zero-length stream operations. Malicious guests can perform zero-length component model stream reads or writes with unvalidated addresses, causing Direct{Source,Destination}::remaining to panic and crash WASIp3 embedders.

CVSS 4.0 · 5.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-119139

Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 Host Panic via Func::call

Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a leftover assertion in component::Func::call that rejects guest exports using the async ABI option. An attacker who supplies a component with an async-lifted export can crash the host process when an embedder invokes that export through Func::call.

CVSS 4.0 · 5.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-119135

Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 Panic via StreamReader Type Mismatch

Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 panics when the host reads a component model stream as a different Rust item type than it was created with, because the host-to-host read path asserts matching TypeIds instead of returning an error. Guest code can return a host-created StreamReader<U> that the embedder reads as StreamReader<T>, where both types map to the same component model type, crashing the embedding process.

CVSS 4.0 · 5.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-119131

Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 Host Panic via wasi-http

Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a denial of service vulnerability in wasmtime-wasi-http that lets guests crash the host by sending long request URLs. Guests can use set-path-with-query with a '?' after byte 65535, overflowing a u16 index in the http crate and triggering a host panic.

CVSS 4.0 · 6.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-121440

Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 Forwarded Trailers Header Filter Bypass

Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 fails to check forwarded trailers against the WasiHttpHooks::is_forbidden_header hook in wasi-http p3. WASIp3 guests can forward a request or response body so its trailers skip embedder-customized forbidden header filtering, undermining header restrictions the embedder intended.

CVSS 4.0 · 6.3 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-121441

Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 wasi-http Request Smuggling

Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 contains a request smuggling vulnerability in wasi-http that allows guests to set multiple conflicting content-length headers. Malicious guests can make the host send HTTP requests with conflicting content-length values to smuggle requests through servers or intermediaries that do not reject them.

CVSS 4.0 · 6.3 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-119140

Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 Host Panic via thread.yield

Wasmtime 46.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains a denial of service vulnerability that allows malicious components to panic the host via thread.yield in start functions. Attackers can supply a component whose start function calls an async-lowered import then thread.yield, causing an undisposed fiber drop that crashes embedders.

CVSS 4.0 · 5.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-119136

Wasmtime 42.0.0 before 48.0.6 and 49.0.0 before 49.0.3 Async-Entrypoint Enforcement Bypass

Wasmtime 42.0.0 before 48.0.6 and 49.0.0 before 49.0.3 contains insufficient checks in Store when mixing async-style and sync-style WebAssembly calls. Embedders re-entering WebAssembly via sync APIs from host functions called asynchronously can trigger runtime panics or unsound cross-thread movement of !Send host variables.

CVSS 4.0 · 5.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime

CVE-2026-119132

Wasmtime 49.0.0 before 49.0.3 Host Panic via Overlapping String Transcode in Fused Adapter

Wasmtime from 49.0.0 before 49.0.3 contains a denial-of-service vulnerability that allows a WebAssembly guest to trigger a host panic by transcoding overlapping strings in fused adapters. Attackers can make a same-instance component-to-component call transferring a string whose source and destination alias each other, crashing the host instead of raising a trap.

CVSS 4.0 · 5.9 Medium EPSS < 1% KEV · Not listed

Vendors

Bytecodealliance

Products

Wasmtime