CVE-2026-34941

Wasmtime contains a vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units.

This vulnerability can cause the host to read beyond the end of a WebAssembly's linear memory in an attempt to transcode nonexistent bytes. In Wasmtime's default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16.

A host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled.

This is an out-of-bounds memory access. Any user running untrusted wasm components that use cross-component string passing (with UTF-16 source and latin1+utf16 destination encodings) is affected.

• With guard pages: Denial of service. The host process crashes with SIGBUS/SIGSEGV.
• Without guard pages: Potential information disclosure. The guest can read host memory beyond its linear memory allocation.

A read operation accesses a memory location beyond the intended buffer boundary. Typical impact: sensitive data disclosure or crash.

CVE-2026-34941 has a CVSS score of 8.1 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (24.0.7, 36.0.7, 42.0.2, 43.0.1); upgrading removes the vulnerable code path.

Kodem intelligence

Wasmtime 24.0.7, 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.
Workarounds

There is no workaround for this bug. Hosts are recommended to updated to a patched version of Wasmtime.

1. What is CVE-2026-34941? CVE-2026-34941 is a medium-severity out-of-bounds read vulnerability in wasmtime (rust), affecting versions < 24.0.7. It is fixed in 24.0.7, 36.0.7, 42.0.2, 43.0.1. A read operation accesses a memory location beyond the intended buffer boundary.
2. How severe is CVE-2026-34941? CVE-2026-34941 has a CVSS score of 8.1 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of wasmtime are affected by CVE-2026-34941? wasmtime (rust) versions < 24.0.7 is affected.
4. Is there a fix for CVE-2026-34941? Yes. CVE-2026-34941 is fixed in 24.0.7, 36.0.7, 42.0.2, 43.0.1. Upgrade to this version or later.
5. Is CVE-2026-34941 exploitable, and should I be worried? Whether CVE-2026-34941 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-34941 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-34941?
   • Upgrade wasmtime to 24.0.7 or later
   • Upgrade wasmtime to 36.0.7 or later
   • Upgrade wasmtime to 42.0.2 or later
   • Upgrade wasmtime to 43.0.1 or later