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CriticalVulnerabilityupdated 26 Oct 2026, 13:13 UTC

Wasmtime flaws could let malicious WebAssembly code escape its sandbox

Wasmtime is a tool that runs WebAssembly programs in a sealed box so they cannot touch the rest of a computer. Two serious bugs could let a malicious program break out of that box.

Fix available1 source, unconfirmed
SeverityCriticalVulnerability
Being exploited?UnclearNo reports either way yet
Fix available?YesFixed versions were released; the exact version numbers are not stated in the available material. · since 26 Oct 2026
How sure is this?1 source, unconfirmedOnly one publisher so far, details may change

How the attack works simplified

  1. 1Malicious authorCrafts a WebAssembly module
  2. 2Module compiledVulnerable Wasmtime build compiles it
  3. 3Module runsExecutes inside the intended sandbox
  4. 4Sandbox escapeFlaw lets code break out of the box
  5. ResultModule gains access beyond its sandbox

What happened

Two critical vulnerabilities in the Wasmtime WebAssembly runtime could allow a malicious WebAssembly module to escape its sandbox. One of the flaws affects only ARM64 systems.

Why it is dangerous: A sandbox escape can let attacker code reach data and resources the host application meant to isolate, which is especially risky in multi-tenant or plugin-based systems that run untrusted WebAssembly.

Are you affected?

You are affected if you run a vulnerable Wasmtime build that compiles untrusted WebAssembly modules, and the ARM64-specific flaw applies only to ARM64 systems.

Vulnerable Wasmtime builds (exact versions not stated in the source).

What to do

  1. Update Wasmtime to the fixed version released by the project
  2. Prioritize updates on ARM64 systems, where one of the flaws applies
  3. Only compile and run WebAssembly modules from trusted sources until patched

Timeline

  1. 26 Oct 2026, 11:52 UTC
    Publicly disclosed
  2. 26 Oct 2026, 11:52 UTC
    Reported by The Hacker News · The Hacker News
  3. 26 Oct 2026, 13:13 UTC
    Picked up by Zero Radar

Sources 1 report, oldest first

Security press established security newsrooms

Technical details

ID
ZR-a5411bb3
Disclosed
26 Oct 2026, 11:52 UTC
On Zero Radar
26 Oct 2026, 13:13 UTC (1 h after disclosure)
Last change
26 Oct 2026, 13:13 UTC

The plain-language parts and the attack diagram were written by an AI model (anthropic/claude-haiku-5.5) from the sources above. Facts like versions, exploitation and dates come from the sources themselves. How Zero Radar works

Wasmtime flaws could let malicious WebAssembly code escape its sandbox · Zero Radar