High severity · published Apr 9, 2026
CVE-2026-34943
Wasmtime panics when lifting `flags` component value
7.5
CVSS
0.3%
EPSS
No
On KEV
Description
Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime contains a possible panic which can happen when a flags-typed component model value is lifted with the Val type. If bits are set outside of the set of flags the component model specifies that these bits should be ignored but Wasmtime will panic when this value is lifted. This panic only affects wasmtime's implementation of lifting into Val, not when using the flags! macro. This additionally only affects flags-typed values which are part of a WIT interface. This has the risk of being a guest-controlled panic within the host which Wasmtime considers a DoS vector. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 25% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
WA
wasmtime · bytecodealliance
< 24.0.7; >= 25.0.0, < 36.0.7; >= 37.0.0, < 42.0.2; >= 43.0.0, < 44.0.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34943
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-34943
Vendor Advisory
https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m758-wjhj-p3jq
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