CVE-2026-34946
Bytecodealliance Wasmtime 25.0.0 – 36.0.7
Raw vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/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:XCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-34946 is a medium-severity Always-Incorrect Control Flow Implementation (CWE-670) vulnerability in Bytecodealliance Wasmtime. Its CVSS base score is 5.9 (Medium).
Operationally, ranked at the 29th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-34946 is a vulnerability in Wasmtime, a runtime for WebAssembly, affecting versions from 25.0.0 up to but not including 36.0.7, 42.0.2, and 43.0.1. The issue lies in the Winch compiler, where compilation of the table.fill instruction can trigger a host panic due to a historical refactoring that incorrectly updated table indexing in Winch code paths. This leads to mixing up tables or referencing nonexistent ones, classified under CWE-670 with a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
The vulnerability can be exploited by any unauthenticated remote attacker who provides a valid WebAssembly guest module to a Wasmtime instance using the Winch compiler on any architecture. Successful exploitation causes the host process to panic, resulting in a denial-of-service condition without impacting confidentiality or integrity.
According to the Wasmtime security advisory, the issue is mitigated by upgrading to fixed versions 36.0.7, 42.0.2, or 43.0.1. Additional details are available at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-q49f-xg75-m9xw.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-21025
Vulnerability Data
Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Winch compiler contains a vulnerability where the compilation of the table.fill instruction can result in a host panic. This means that a valid guest can…
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be compiled with Winch, on any architecture, and cause the host to panic. This represents a denial-of-service vulnerability in Wasmtime due to guests being able to trigger a panic. The specific issue is that a historical refactoring changed how compiled code referenced tables within the table.* instructions. This refactoring forgot to update the Winch code paths associated as well, meaning that Winch was using the wrong indexing scheme. Due to the feature support of Winch the only problem that can result is tables being mixed up or nonexistent tables being used, meaning that the guest is limited to panicking the host (using a nonexistent table), or executing spec-incorrect behavior and modifying the wrong table. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.
- CWE(s)
Related Threats
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V9.2.1
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation at post-design stages directly exercises control-flow paths and reveals mismatches between implemented and intended behavior.
Requiring a documented development process and supporting tools reduces the chance that incorrect control-flow logic is introduced in the first place.
Flaw identification and remediation processes can locate and correct control-flow errors once they manifest as incorrect runtime behavior.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly prevent incorrect control-flow implementations via reviews, testing, and static analysis.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development and acceptance can detect paths that deviate from intended logic.
Secure development lifecycle processes can catch incorrect control-flow logic during design and code review.
Secure coding standards and reviews directly target flawed control-flow implementations.
Change-management gates may prevent deployment of flawed logic but do not address the coding defect itself.