---
id: "CVE-2026-54913"
kind: "vulnerability"
aliases: ["CVE-2026-54913"]
title: "WAMR: crafted Wasm module leaks uninitialized host stack bytes to guest"
severity: "medium"
cvss: 6.9
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["embedded-wasm", "runtime", "wamr", "webassembly"]
not_affected_if: ["gc-enabled", "trusted-modules-only"]
published_at: "2026-11-05T18:17:08+00:00"
first_seen_at: "2026-11-05T18:40:09+00:00"
updated_at: "2026-11-05T18:40:37+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-54913", "first_seen_at": "2026-11-05T18:40:09+00:00"}]
exploit_sources: []
---

# WAMR: crafted Wasm module leaks uninitialized host stack bytes to guest

WebAssembly Micro Runtime (WAMR) before 2.4.5 accepts an invalid ref.null heap-type byte in global initializers when GC is disabled, so uninitialized host-stack memory is copied into a guest-readable global. A crafted module can read leftover host memory, up to twelve bytes per v128 global.

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

## How to check

- Check the WAMR version in use, for example with `iwasm --version` or the version of the embedded library, and see whether it is below `2.4.5`.
- Check whether the build sets `WASM_ENABLE_GC=0`, the default no-GC configuration.
- Check whether the runtime loads untrusted or user-supplied Wasm modules.

## Fix

- WAMR: upgrade to `2.4.5`

## Timeline

- 2026-11-05T18:40:09+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-54913

## Documents

- [advisory] Vendor advisory: github.com https://github.com/wasm-micro-runtime/wasm-micro-runtime/security/advisories/GHSA-frwm-5hpr-2hq2
- [fix] Patch: github.com https://github.com/wasm-micro-runtime/wasm-micro-runtime/commit/c313279c548c6a93f55eb97455cab8696e39f6c1
- [fix] Patch: github.com https://github.com/wasm-micro-runtime/wasm-micro-runtime/commit/e571797fbdf498d9ac4edb495205ea0f01370091
- [fix] Release notes: github.com https://github.com/wasm-micro-runtime/wasm-micro-runtime/releases/tag/WAMR-2.4.5

## From the sources

WebAssembly Micro Runtime (WAMR) is a lightweight standalone WebAssembly (Wasm) runtime. Prior to 2.4.5, load_init_expr in core/iwasm/interpreter/wasm_loader.c accepts a non-reference heap-type byte for ref.null when WASM_ENABLE_GC=0, while the local WASMValue cur_value union is not zero-initialized and setting ref_index writes only part of it. A crafted module can declare an i64, f64, or v128 global initialized through the invalid ref.null form, causing push_const_expr_stack and the later global initialization path to copy uninitialized host-stack bytes into a value readable by the guest. The classic and fast interpreters are affected in the default no-GC configuration; the GC-enabled path validates heap types. The disclosure is four bytes for i64 or f64 globals and up to twelve bytes for each v128 global. This issue is fixed in version 2.4.5.

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