CVE-2026-54786 Wasmtime: Leak in WASIp1 `fd_renumber` implementation

What is CVE-2026-54786?

CVE-2026-54786 is a low-severity denial of service vulnerability in bytecodealliance wasmtime, published on 1 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Wasmtime is a runtime for WebAssembly. All versions prior to 24.0.10; versions 25.0.0 through those before 36.0.11; versions 37.0.0 through those before 44.0.3; and versions 45.0.0 and 45.0.1 contain a native implementation of WASIp1 which suffers from a leak in the fd_renumber function where the file descriptor being renumbered to is not properly closed. Wasmtime's implementation erroneously only updated the table of descriptors for WASIp1 and didn't update the underlying table of descriptors used by the host. This behavior means that while fd_renumber works correctly from a guest's perspective it ends up leaking resources in the host that aren't cleaned up until the corresponding Store is destroyed. In a loop, guests can use fd_renumber to cause hosts to exhaust both resources and file descriptors. This bug only affects the native implementation of WASIp1, meaning that only runtimes which load core wasm modules and expose fd_renumber are affected. Runtimes are additionally only affected if they expose the ability to acquire a file descriptor, such as opening a file. For runtimes that deny access to files they are unaffected. This issue has been fixed in versions 24.0.10, 36.0.11, 44.0.3, and 45.0.2.

Weakness: CWE-772, CWE-400

Which versions are affected by CVE-2026-54786?

9 open source packages ship an affected version, including wasmtime-wasi. It affects 1 product.

Products include Bytecodealliance Wasmtime.

How do I fix CVE-2026-54786?

Upgrade wasmtime-wasi to a fixed version for your release line: 24.0.10, 36.0.11, 44.0.3 or 45.0.2.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-54786 being exploited?

There is no known exploitation of CVE-2026-54786 in the wild and no public exploit code.

Other vulnerabilities in bytecodealliance wasmtime

• CVE-2026-34971 Wasmtime miscompiled guest heap access enables sandbox escape on aarch64 Cranelift Critical 9.0
• CVE-2026-34987 Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access Critical 9.0
• CVE-2022-39393 Wasmtime vulnerable to data leakage between instances in the pooling allocator High 8.6
• CVE-2022-24791 Use after free in Wasmtime High 8.1
• CVE-2026-47261 Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction High 7.5

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2026-54786, GHSA-3p27-qvp9-27qf, JLSEC-2026-1367, MINI-cx8g-cc87-9wcv, MINI-q5m8-f2cv-pr3j, MINI-w46j-9jc9-7p3m and 2 more.