CVE-2026-24116

Wasmtime segfault or unused out-of-sandbox load with f64.copysign operator on x86-64

Published Jan 27, 2026 CVSS 4.0 · 4.1 Medium EPSS < 1% KEV · Not listed

Description

Wasmtime is a runtime for WebAssembly. Starting in version 29.0.0 and prior to version 36.0.5, 40.0.3, and 41.0.1, on x86-64 platforms with AVX, Wasmtime's compilation of the `f64.copysign` WebAssembly instruction with Cranelift may load 8 more bytes than is necessary. When signals-based-traps are disabled this can result in a uncaught segfault due to loading from unmapped guard pages. With guard pages disabled it's possible for out-of-sandbox data to be loaded, but unless there is another bug in Cranelift this data is not visible to WebAssembly guests. Wasmtime 36.0.5, 40.0.3, and 41.0.1 have been released to fix this issue. Users are recommended to upgrade to the patched versions of Wasmtime. Other affected versions are not patched and users should updated to supported major version instead. This bug can be worked around by enabling signals-based-traps. While disabling guard pages can be a quick fix in some situations, it's not recommended to disabled guard pages as it is a key defense-in-depth measure of Wasmtime.

Analysis

Technical impact

This flaw occurs in the Wasmtime runtime when compiling the WebAssembly instruction f64.copysign on x86‑64 machines that support AVX. The generated code may load eight bytes beyond the intended operand, which can trigger an uncaught segfault if signals‑based‑traps are disabled, or may cause data from outside the sandbox to be read when guard pages are disabled. The crash represents a denial‑of‑service attack; the out‑of‑bounds read does not leak guest memory because the extra load is not visible to WebAssembly modules, making it a classic out‑of‑bounds read weakness (CWE‑125).

Affected Systems

The issue applies to the bytecodealliance Wasmtime runtime on x86‑64 platforms with AVX support. Vulnerable versions span from 29.0.0 up to, but not including, the patched releases 36.0.5, 40.0.3, and 41.0.1. Users should update to one of those releases or to a later major version that contains the fix.

Risk and Exploitability

With a CVSS score of 4.1 the severity is low, and an EPSS score of less than 1 % indicates a very low probability of exploitation. The defect causes a process crash rather than allowing remote code execution or memory disclosure; thus the overall risk is mild. No CISA KEV listing is present. The attack vector is local—any component that feeds WebAssembly code into Wasmtime can trigger the failure if signals‑based‑traps are disabled or guard pages are turned off.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

bytecodealliance

wasmtime

affected

Version	Status	Constraints
`>= 29.0.0, < 36.0.5`	affected	—
`>= 37.0.0, < 40.0.3`	affected	—
`= 41.0.0`	affected	—

Configuration 1 [-]

OR	cpe:2.3:a:bytecodealliance:wasmtime::::::rust::*
	cpe:2.3:a:bytecodealliance:wasmtime::::::rust::*
	cpe:2.3:a:bytecodealliance:wasmtime::::::rust::*

No data.

Vendor	Product	Versions
Bytecodealliance	Wasmtime	—

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade Wasmtime to at least version 36.0.5 for the current major line, or to 40.0.3 or 41.0.1; any newer release includes the fix.
If upgrading cannot be performed immediately, enable signals‑based‑traps in the Wasmtime configuration to avoid the segfault.
Avoid disabling guard pages, as they are a critical defense‑in‑depth measure preventing out‑of‑sandbox reads.

Generated by OpenCVE AI on April 18, 2026 at 01:58 UTC.

Tracking

Advisories

Source	ID	Title
Github GHSA	GHSA-vc8c-j3xm-xj73	Wasmtime segfault or unused out-of-sandbox load with f64.copysign operator on x86-64

Metrics

Attack Vector Local

Attack Complexity Low

Privileges Required Low

Attack Requirements Present

User Interaction Active

Vulnerable System Confidentiality Impact None

Vulnerable System Integrity Impact None

Vulnerable System Availability Impact High

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Local

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction Required

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.244% probability within 30 days)

Exploitation none

Automatable no

Technical Impact partial

References

Link	Providers
https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#method.memory_guard_size
https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#method.signals_based_traps
https://docs.wasmtime.dev/stability-release.html
https://github.com/bytecodealliance/wasmtime/commit/728fa07184f8da2a046f48ef9b61f869dce133a6
https://github.com/bytecodealliance/wasmtime/commit/799585fc362fcb991de147dd1a9f2ba0861ed440
https://github.com/bytecodealliance/wasmtime/commit/ac92d9bb729ad3a6d93f0724c4c33a0c4a9c0227
https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-vc8c-j3xm-xj73
https://rustsec.org/advisories/RUSTSEC-2026-0006.html

History

Feb 12, 2026 9:45 PM Affected versions updated. Scoring metrics updated View changes

Type	Values Removed	Values Added
CPEs		cpe:2.3:a:bytecodealliance:wasmtime::::::rust::*
Metrics		cvssV3_1 `{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H'}`

Jan 28, 2026 12:30 PM First appearance in the feed. Affected vendors updated View changes

Type	Values Removed	Values Added
First Time appeared		Bytecodealliance Bytecodealliance wasmtime
Vendors & Products		Bytecodealliance Bytecodealliance wasmtime

Jan 27, 2026 8:15 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Jan 27, 2026 7:15 PM Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
Description		Wasmtime is a runtime for WebAssembly. Starting in version 29.0.0 and prior to version 36.0.5, 40.0.3, and 41.0.1, on x86-64 platforms with AVX, Wasmtime's compilation of the `f64.copysign` WebAssembly instruction with Cranelift may load 8 more bytes than is necessary. When signals-based-traps are disabled this can result in a uncaught segfault due to loading from unmapped guard pages. With guard pages disabled it's possible for out-of-sandbox data to be loaded, but unless there is another bug in Cranelift this data is not visible to WebAssembly guests. Wasmtime 36.0.5, 40.0.3, and 41.0.1 have been released to fix this issue. Users are recommended to upgrade to the patched versions of Wasmtime. Other affected versions are not patched and users should updated to supported major version instead. This bug can be worked around by enabling signals-based-traps. While disabling guard pages can be a quick fix in some situations, it's not recommended to disabled guard pages as it is a key defense-in-depth measure of Wasmtime.
Title		Wasmtime segfault or unused out-of-sandbox load with f64.copysign operator on x86-64
Weaknesses		CWE-125
References		https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#method.memory_guard_size https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#method.signals_based_traps https://docs.wasmtime.dev/stability-release.html https://github.com/bytecodealliance/wasmtime/commit/728fa07184f8da2a046f48ef9b61f869dce133a6 https://github.com/bytecodealliance/wasmtime/commit/799585fc362fcb991de147dd1a9f2ba0861ed440 https://github.com/bytecodealliance/wasmtime/commit/ac92d9bb729ad3a6d93f0724c4c33a0c4a9c0227 https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-vc8c-j3xm-xj73 https://rustsec.org/advisories/RUSTSEC-2026-0006.html
Metrics		cvssV4_0 `{'score': 4.1, 'vector': 'CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}`