CVE-2026-34987
9.9 · CRITICALOverview
CVE-2026-34987 is a critical-severity vulnerability affecting bytecodealliance wasmtime. It was published on April 9, 2026 and has a CVSS 3.1 base score of 9.9 (CRITICAL).
This vulnerability has a CVSS 3.1 base score of 9.9, rated CRITICAL. It can be exploited remotely over the network. Some level of privileges is required for exploitation.
Technical Description
Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime with its Winch (baseline) non-default compiler backend may allow properly constructed guest Wasm to access host memory outside of its linear-memory sandbox. This vulnerability requires use of the Winch compiler (-Ccompiler=winch). By default, Wasmtime uses its Cranelift backend, not Winch. With Winch, the same incorrect assumption is present in theory on both aarch64 and x86-64. The aarch64 case has an observed-working proof of concept, while the x86-64 case is theoretical and may not be reachable in practice. This Winch compiler bug can allow the Wasm guest to access memory before or after the linear-memory region, independently of whether pre- or post-guard regions are configured. The accessible range in the initial bug proof-of-concept is up to 32KiB before the start of memory, or ~4GiB after the start of memory, independently of the size of pre- or post-guard regions or the use of expl
Remediation
Check the references section for vendor advisories and patches from bytecodealliance. Update wasmtime to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| bytecodealliance | wasmtime | >= 25.0.0, < 36.0.7 | Affected |
Frequently Asked Questions
What is CVE-2026-34987?
CVE-2026-34987 is a critical-severity vulnerability affecting bytecodealliance wasmtime. It was published on April 9, 2026 and has a CVSS 3.1 base score of 9.9 (CRITICAL).
How severe is CVE-2026-34987?
This vulnerability has a CVSS 3.1 base score of 9.9, rated CRITICAL. It can be exploited remotely over the network. Some level of privileges is required for exploitation.
How do I fix or remediate CVE-2026-34987?
Check the references section for vendor advisories and patches from bytecodealliance. Update wasmtime to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2026-34987?
CyberStrike's AI-powered security agents can automatically detect CVE-2026-34987 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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