CVE-2026-34943 — Wasmtime panics when lifting `flags` component value

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.

Published Apr 9, 2026Updated Apr 13, 2026Sources: cvelistV5, GitHub_M

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Unreported

no source claims exploitation

EPSS

chance of exploitation in 30 days

Affects

bytecodealliance

wasmtime

CVSS base

5.6

MEDIUM

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

None

none · proof-of-concept · active

Automatable

Yes

can an attacker script all four kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Affected scope

The catalog records vendors and products as separate lists, not pairs, so which product belongs to which vendor is not something this page can say.

Vendors (1)

bytecodealliance

Products (1)

wasmtime

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
5.6	CVSS 4.0	MEDIUM	—	—	cvelistV5

Weakness & attack patterns

CWE-248

References

1 on the record

github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m758-wjhj-p3jq
x_refsource_CONFIRM

Elsewhere on this site

bytecodeallianceevery CVE for this vendor
CWE-248other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.