{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-34987","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","state":"PUBLISHED","assignerShortName":"GitHub_M","dateReserved":"2026-03-31T19:38:31.617Z","datePublished":"2026-04-09T18:48:33.552Z","dateUpdated":"2026-04-10T14:12:55.374Z"},"containers":{"cna":{"title":"Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access","problemTypes":[{"descriptions":[{"cweId":"CWE-125","lang":"en","description":"CWE-125: Out-of-bounds Read","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-787","lang":"en","description":"CWE-787: Out-of-bounds Write","type":"CWE"}]}],"metrics":[{"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"LOW","userInteraction":"NONE","vulnConfidentialityImpact":"HIGH","vulnIntegrityImpact":"HIGH","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"HIGH","subIntegrityImpact":"HIGH","subAvailabilityImpact":"HIGH","baseScore":9,"baseSeverity":"CRITICAL","vectorString":"CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H","version":"4.0"}}],"references":[{"name":"https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-xx5w-cvp6-jv83","tags":["x_refsource_CONFIRM"],"url":"https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-xx5w-cvp6-jv83"}],"affected":[{"vendor":"bytecodealliance","product":"wasmtime","versions":[{"version":">= 25.0.0, < 36.0.7","status":"affected"},{"version":">= 37.0.0, < 42.0.2","status":"affected"},{"version":">= 43.0.0, < 44.0.1","status":"affected"}]}],"providerMetadata":{"orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","shortName":"GitHub_M","dateUpdated":"2026-04-09T18:48:33.552Z"},"descriptions":[{"lang":"en","value":"Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime with its Winch (baseline) non-default compiler backend may allow properly constructed guest Wasm to access host memory outside of its linear-memory sandbox. This vulnerability requires use of the Winch compiler (-Ccompiler=winch). By default, Wasmtime uses its Cranelift backend, not Winch. With Winch, the same incorrect assumption is present in theory on both aarch64 and x86-64. The aarch64 case has an observed-working proof of concept, while the x86-64 case is theoretical and may not be reachable in practice. This Winch compiler bug can allow the Wasm guest to access memory before or after the linear-memory region, independently of whether pre- or post-guard regions are configured. The accessible range in the initial bug proof-of-concept is up to 32KiB before the start of memory, or ~4GiB after the start of memory, independently of the size of pre- or post-guard regions or the use of explicit or guard-region-based bounds checking. However, the underlying bug assumes a 32-bit memory offset stored in a 64-bit register has its upper bits cleared when it may not, and so closely related variants of the initial proof-of-concept may be able to access truly arbitrary memory in-process. This could result in a host process segmentation fault (DoS), an arbitrary data leak from the host process, or with a write, potentially an arbitrary RCE. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1."}],"source":{"advisory":"GHSA-xx5w-cvp6-jv83","discovery":"UNKNOWN"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-04-10T14:12:37.362283Z","id":"CVE-2026-34987","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-04-10T14:12:55.374Z"}}]}}