CVE-2026-34943
CVE-2026-34943 is a high-severity vulnerability in Bytecodealliance Wasmtime with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-248.
Key facts
- Severity: High (CVSS 3.x base score 7.5)
- CVSS v4: 5.6
- EPSS exploit prediction: 0% (24th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-21022
- Weakness: CWE-248
- Affected product: Bytecodealliance Wasmtime
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2026-34943?
- 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.
- How severe is CVE-2026-34943?
- CVE-2026-34943 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
- Is CVE-2026-34943 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (24th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-34943?
- CVE-2026-34943 affects Bytecodealliance Wasmtime. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-34943?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
- Does CVE-2026-34943 have an EU (EUVD) identifier?
- Yes. CVE-2026-34943 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-21022.
- When was CVE-2026-34943 published?
- CVE-2026-34943 was published on 2026-04-09 and last updated on 2026-06-17.
References
Affected products (1)
- cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:*
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