CVE-2026-34943

// This is a conceptual PoC for WIT interface interaction. // Vulnerable Context: Lifting a flag value with extraneous bits using Val. // WIT Definition (example): // package my:pkg; // interface flags { // enum my-flags { a, b } // } // Exploit Scenario: // The guest (malicious Wasm) sets a bit outside 'a' or 'b', e.g., bit 2 (value 4). // When the host tries to lift this value into a `Val` type (e.g., for inspection or reflection), // the vulnerable Wasmtime version will panic instead of masking out the invalid bit. // Rust Host-side pseudo-code demonstrating the crash condition: /* fn lift_flags_value(raw_bits: u8) -> Val { // In vulnerable versions (< 24.0.7, etc.), passing raw_bits = 0b00000100 // when only bits 0 and 1 are defined causes a panic here. let val = Val::from_flags(raw_bits); val } // Trigger: // lift_flags_value(0b00000100); // Panic! DoS triggered. */

{"cve": {"id": "CVE-2026-34943", "sourceIdentifier": "[email protected]", "published": "2026-04-09T19:16:24.020", "lastModified": "2026-04-20T18:28:03.000", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "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."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:A/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:X", "baseScore": 5.6, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "HIGH", "attackRequirements": "PRESENT", "privilegesRequired": "HIGH", "userInteraction": "ACTIVE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "confidentialityRequirement": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "availabilityRequirement": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED"}}], "cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-248"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:*", "versionEndExcluding": "24.0.7", "matchCriteriaId": "5A39DBFB-CD5E-4551-8885-053DF90E277A"}, {"vulnerable": true, "criteria": "cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:*", "versionStartIncluding": "25.0.0", "versionEndExcluding": "36.0.7", "matchCriteriaId": "B5AB2157-3977-49F9-9058-6B16A2556170"}, {"vulnerable": true, "criteria": "cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:*", "versionStartIncluding": "37.0.0", "versionEndExcluding": "42.0.2", "matchCriteriaId": "1D7B70EB-93E3-4732-AB70-E6A531178941"}, {"vulnerable": true, "criteria": "cpe:2.3:a:bytecodealliance:wasmtime:*:*:*:*:*:rust:*:*", "versionStartIncluding": "43.0.0", "versionEndExcluding": "43.0.1", "matchCriteriaId": "15FD6AA4-973B-4647-9222-40FBDC16A6FD"}]}]}], "references": [{"url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m758-wjhj-p3jq", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}