---
id: "CVE-2026-126407"
page: "https://infrastack.ai/live/CVE-2026-126407"
kind: "vulnerability"
aliases: ["CVE-2026-126407"]
title: "Wasmtime: untracked borrowed resources let a guest exhaust host memory"
severity: "medium"
cvss: 5.9
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["runtime", "self-hosted", "wasmtime", "webassembly"]
not_affected_if: ["no-component-model", "trusted-guests-only"]
published_at: "2026-11-13T10:17:45+00:00"
first_seen_at: "2026-11-13T10:47:19+00:00"
updated_at: "2026-11-13T10:56:44+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-126407", "first_seen_at": "2026-11-13T10:47:19+00:00"}]
exploit_sources: []
---

# Wasmtime: untracked borrowed resources let a guest exhaust host memory

Link for people: https://infrastack.ai/live/CVE-2026-126407 (this .md is for agents)

Wasmtime allocates host memory for borrowed resources without counting them against the per-store handle limit. A malicious guest component can repeat these transfers to consume arbitrary host memory and cause a denial of service.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the Wasmtime version your application links against, for example `wasmtime --version` or the crate version in `Cargo.lock`.
- Confirm whether you run untrusted WebAssembly component guests in your process.

## Fix

- Wasmtime `36.0.20`
- Wasmtime `48.0.8`
- Wasmtime `49.0.5`
- Wasmtime `50.0.1`

## Timeline

- 2026-11-13T10:47:19+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-126407

## Documents

- [advisory] Vendor advisory: github.com https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-6fr9-xmw9-5352
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/wasmtime-before-36.0.20-denial-of-service-via-borrowed-resource-transfer

## From the sources

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.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_