CVE-2026-35195: Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime's implementation of transcoding strings between component...

Description

Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime's implementation of transcoding strings between components contains a bug where the return value of a guest component's realloc is not validated before the host attempts to write through the pointer. This enables a guest to cause the host to write arbitrary transcoded string bytes to an arbitrary location up to 4GiB away from the base of linear memory. These writes on the host could hit unmapped memory or could corrupt host data structures depending on Wasmtime's configuration. Wasmtime by default reserves 4GiB of virtual memory for a guest's linear memory meaning that this bug will by default on hosts cause the host to hit unmapped memory and abort the process due to an unhandled fault. Wasmtime can be configured, however, to reserve less memory for a guest and to remove all guard pages, so some configurations of Wasmtime may lead to corruption of data outside of a guest's linear memory, such as host data structures or other guests's linear memories. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.

Metrics

CVSS 3.1

5.4/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

CVSS 4.0

6.1/10

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.22%

11.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-787

Affected Software

Vendor	Product	Versions
Bytecodealliance	Wasmtime	< 24.0.7
Bytecodealliance	Wasmtime	>= 25.0.0, < 36.0.7
Bytecodealliance	Wasmtime	>= 37.0.0, < 42.0.2
Bytecodealliance	Wasmtime	43.0.0

References

https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-394w-hwhg-8vgmVendor Advisory

Timeline

Published: Apr 9, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-35195?

Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime's implementation of transcoding strings between components contains a bug where the return value of a guest component's realloc is not validated before the host attempts to write through the pointer. This enables a guest to cause the host to write arbitrary transcoded string bytes to an arbitrary location up to 4GiB away from the base of linear memory. These writes on the host could hit unmapped memory or could corrupt host data structures depending on Wasmtime's configuration. Wasmtime by default reserves 4GiB of virtual memory for a guest's linear memory meaning that this bug will by default on hosts cause the host to hit unmapped memory and abort the process due to an unhandled fault. Wasmtime can be configured, however, to reserve less memory for a guest and to remove all guard pages, so some configurations of Wasmtime may lead to corruption of data outside of a guest's linear memory, such as host data structures or other guests's linear memories. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.

How severe is CVE-2026-35195?

CVE-2026-35195 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 0.22% probability of exploitation in the next 30 days.

How do I fix CVE-2026-35195?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.