CVE-2026-54786

Wasmtime has a leak in WASIp1 fd_renumber implementation

Workarounds

There are no workarounds for this issue and hosts are recommended to update.

Wasmtime's native implementation of WASIp1 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. This means that guests can, in a loop, use fd_renumber to cause hosts to exhaust resources or exhaust file descriptors.

This bug only affects the native implementation of WASIp1. This means 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.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2026-54786 has a CVSS score of 5.0 (Low). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (24.0.10, 45.0.2, 36.0.11, 44.0.3); upgrading removes the vulnerable code path.

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Wasmtime 24.0.10, 36.0.11, 44.0.3, and 45.0.2 have been released which fix this issue.

1. What is CVE-2026-54786? CVE-2026-54786 is a low-severity uncontrolled resource consumption vulnerability in wasmtime-wasi (rust), affecting versions < 24.0.10. It is fixed in 24.0.10, 45.0.2, 36.0.11, 44.0.3. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-54786? CVE-2026-54786 has a CVSS score of 5.0 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of wasmtime-wasi are affected by CVE-2026-54786? wasmtime-wasi (rust) versions < 24.0.10 is affected.
4. Is there a fix for CVE-2026-54786? Yes. CVE-2026-54786 is fixed in 24.0.10, 45.0.2, 36.0.11, 44.0.3. Upgrade to this version or later.
5. Is CVE-2026-54786 exploitable, and should I be worried? Whether CVE-2026-54786 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-54786 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-54786?
   • Upgrade wasmtime-wasi to 24.0.10 or later
   • Upgrade wasmtime-wasi to 45.0.2 or later
   • Upgrade wasmtime-wasi to 36.0.11 or later
   • Upgrade wasmtime-wasi to 44.0.3 or later