Wasmtime Async Callback Stack Overflow CVE-2026-115384 Risks Host Compromise in Old Versions

Wasmtime versions prior to 48.0.4 and 49.0.2 contain a critical stack buffer overflow vulnerability. Malicious WebAssembly guests can exploit unvalidated async callback result types to write approximately 16KB to the native stack.

What happened

The Bytecode Alliance’s Wasmtime runtime contains a flaw in how it handles component-model-async callback functions. According to the National Vulnerability Database record for CVE-2026-115384, attackers can supply components with mistyped callback functions. This allows malicious guests to write roughly 16KB of data directly to the native stack. The vulnerability stems from insufficient validation of async callback result types, classified under CWE-20.

This issue affects Wasmtime versions starting from 39.0.0 up to, but not including, 48.0.4. It also impacts the 49.0.0 branch up to, but not including, 49.0.2. The NVD assigns a CVSS score of 9.4, rating the severity as critical. Successful exploitation can overwrite return addresses on the stack.

Why it matters

Overwriting return addresses enables attackers to crash the host system or execute arbitrary code. This effectively allows a malicious guest to escape the WebAssembly sandbox. As Packet Tribune reported on 2026-10-21 regarding Tenda AC19 firmware flaws, stack overflows in web services often lead to remote code execution. Similarly, the openGauss heap buffer overflow noted on 2026-10-19 demonstrated how ordinary users could trigger dangerous memory writes.

Sandbox escapes undermine the primary security benefit of WebAssembly isolation. Teams relying on Wasmtime for untrusted code execution face significant risk. The ability to write large amounts of data to the native stack provides attackers with substantial control over host execution flow. This elevates the threat from simple denial of service to full host compromise.

Next steps

• Audit all production environments for Wasmtime versions 39.0.0 through 48.0.3.
• Identify any deployments using Wasmtime 49.0.0 or 49.0.1.
• Plan upgrades to Wasmtime 48.0.4 or 49.0.2 as soon as possible.
• Review logs for unexpected crashes or anomalous memory usage in guest workloads.

Detection notes

Security operations teams should monitor for sudden host process crashes originating from Wasmtime services. Look for alerts indicating abnormal memory access patterns or stack corruption errors. Check system logs for repeated failures in async callback handling. Investigate any guest components exhibiting unexpected resource consumption. Isolate affected hosts immediately if sandbox escape indicators appear. Review network traffic for unusual outbound connections from previously contained workloads. Ensure logging captures detailed error messages from the runtime environment.

Background: Firmware

You should enable firmware TPM if your hardware supports it and your operating system requires measured boot sequences. This setting activates a secure cryptographic processor embedded within your main system chipset rather than requiring an external microchip soldered to the motherboard.

Read the full guide: Should I enable firmware TPM and what breaks when you do

What to do and how to stay safe: Wasmtime

• Inventory all systems running Wasmtime to identify vulnerable versions.
• Restrict network access for hosts running unpatched Wasmtime versions.
• Monitor for signs of sandbox escape attempts in real-time.
• Prepare to deploy updates once vendors confirm fixes for affected versions.

Step-by-step guide: Emergency Patching: How to Fix Critical Flaws Without Breaking Production

General security guidance from the Packet Tribune newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

Which Wasmtime versions are affected by CVE-2026-115384?

Versions 39.0.0 before 48.0.4 and 49.0.0 before 49.0.2 are affected.

What is the CVSS score for this vulnerability?

The National Vulnerability Database rates it as critical with a score of 9.4.

How can attackers exploit this flaw?

Attackers supply mistyped component-model-async callback functions to overwrite return addresses.