CVE-2026-34945

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From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, Wasmtime's Winch compiler contains a bug where a 64-bit table, part of the memory64 proposal of WebAssembly, incorrectly translated the table.size instruction. This bug could lead to disclosing data on the host's stack to WebAssembly guests. The host's stack can possibly contain sensitive data related to other host-originating operations which is not intended to be disclosed to guests. This bug specifically arose from a mistake where the return value of table.size was statically typed as a 32-bit integer, as opposed to consulting the table's index type to see how large the returned register could be. When combined with details about Wnich's ABI, such as multi-value returns, this can be combined to read stack data from the host, within a guest. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1."}, {"lang": "es", "value": "Wasmtime es un entorno de ejecuci\u00f3n para WebAssembly. Desde la versi\u00f3n 25.0.0 hasta antes de las versiones 36.0.7, 42.0.2 y 43.0.1, el compilador Winch de Wasmtime contiene un error donde una tabla de 64 bits, parte de la propuesta memory64 de WebAssembly, traduc\u00eda incorrectamente la instrucci\u00f3n table.size. Este error podr\u00eda llevar a la divulgaci\u00f3n de datos de la pila del anfitri\u00f3n a los invitados de WebAssembly. La pila del anfitri\u00f3n posiblemente puede contener datos sensibles relacionados con otras operaciones originadas en el anfitri\u00f3n que no est\u00e1n destinados a ser divulgados a los invitados. Este error surgi\u00f3 espec\u00edficamente de un fallo donde el valor de retorno de table.size fue tipado est\u00e1ticamente como un entero de 32 bits, en lugar de consultar el tipo de \u00edndice de la tabla para ver cu\u00e1n grande podr\u00eda ser el registro devuelto. Cuando se combina con detalles sobre la ABI de Winch, como los retornos de m\u00faltiples valores, esto puede combinarse para leer datos de la pila del anfitri\u00f3n, dentro de un invitado. Esta vulnerabilidad est\u00e1 corregida en las versiones 36.0.7, 42.0.2 y 43.0.1."}], "id": "CVE-2026-34945", "lastModified": "2026-10-26T22:10:00.163", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 6.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N", "version": "3.1"}, "exploitabilityScore": 2.8, "impactScore": 3.6, "source": "nvd@nist.gov", "type": "Primary"}], "cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 2.3, "baseSeverity": "LOW", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "LOW", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "LOW", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/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", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "LOW", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "security-advisories@github.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-34945", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-04-10T14:12:11.204857Z", "version": "2.0.3"}}]}, "published": "2026-04-09T19:16:24.330", "references": [{"source": "security-advisories@github.com", "tags": ["Vendor Advisory"], "url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-681"}], "source": "security-advisories@github.com", "type": "Secondary"}]}

{"bugzilla": {"description": "wasmtime: winch: Wasmtime Winch compiler: Information disclosure via incorrect table.size instruction translation", "id": "2457004", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2457004"}, "csaw": false, "cvss3": {"cvss3_base_score": "5.6", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N", "status": "draft"}, "cwe": "CWE-681", "details": ["A flaw was found in Wasmtime's Winch compiler. This vulnerability, present in versions from 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, arises from an incorrect translation of the `table.size` instruction for 64-bit WebAssembly tables. An attacker, by crafting a malicious WebAssembly guest, could exploit this flaw to read sensitive data from the host's stack. This information disclosure could expose data related to other host operations that should not be accessible to guests."], "mitigation": {"lang": "en:us", "value": "Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability."}, "name": "CVE-2026-34945", "package_state": [{"cpe": "cpe:/a:redhat:connectivity_link:1", "fix_state": "Fix deferred", "package_name": "redhat-user-workloads/rhcl-1-3-wasm-shim", "product_name": "Red Hat Connectivity Link 1"}, {"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Fix deferred", "package_name": "virt-firmware-rs", "product_name": "Red Hat Enterprise Linux 10"}], "public_date": "2026-04-09T18:40:48Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-34945\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-34945\nhttps://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946"], "threat_severity": "Moderate"}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[25.0.0,36.0.7)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[37.0.0,42.0.2)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[43.0.0,44.0.1)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "wasmtime", "source": "cna", "vendor": "bytecodealliance"}, "product": "wasmtime", "vendor": "bytecodealliance"}], "analysis": {"en": {"generated_at": "2026-04-09T22:05:19.627215+00:00", "value": {"mitigation_remediation": ["Upgrade Wasmtime to version 36.0.7, 42.0.2, 43.0.1 or later"], "summary": {"action": "Apply Patch", "impact": "Host Data Exposure"}, "threat_synthesis": {"affected_systems": "Bytecodealliance Wasmtime releases from 25.0.0 up to, but not including, 36.0.7, as well as the versions 42.0.2 and 43.0.1, contain the vulnerability. These releases have been corrected in 36.0.7, 42.0.2, and 43.0.1.", "description_and_impact": "A bug in Wasmtime\u2019s Winch compiler misinterprets the table.size instruction for 64\u2011bit tables, returning a 32\u2011bit value when the correct size is larger. This mismatch allows a WebAssembly guest to read data that resides on the host\u2019s stack, potentially exposing sensitive information that should remain hidden from untrusted guest code. The flaw represents an integer type mismatch weakness (CWE\u2011681).", "risk_and_exploitability": "The CVSS score of 2.3 indicates low overall risk. Based on the description, it is inferred that an attacker must be able to execute WebAssembly code within a vulnerable Wasmtime instance to trigger the leak, suggesting a local or controlled code execution scenario rather than a traditional remote attack vector. No EPSS data is available and the vulnerability is not listed in CISA\u2019s KEV catalog, implying limited current exploit activity, but host systems running untrusted Wasm code remain at risk of accidental data disclosure."}}}}, "created": "2026-04-10T08:39:16.099385+00:00", "updated": "2026-04-10T09:31:39.501982+00:00", "vendors": ["bytecodealliance", "bytecodealliance$PRODUCT$wasmtime"]}