Vulnerability-Lookup

CVE-2026-34945 (GCVE-0-2026-34945)

Vulnerability from cvelistv5 – Published: 2026-04-09 18:40 – Updated: 2026-04-10 14:12

Title

Wasmtime leaks host data with 64-bit tables and Winch

Summary

Wasmtime is a runtime for WebAssembly. 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.

Severity ?

2.3 (Low)


                        
                          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

CWE

CWE-681 - Incorrect Conversion between Numeric Types

Assigner

GitHub_M

References

URL

Tags

https://github.com/bytecodealliance/wasmtime/secu…

x_refsource_CONFIRM

Impacted products

	Vendor	Product	Version
	bytecodealliance	wasmtime	Affected: >= 25.0.0, < 36.0.7 Affected: >= 37.0.0, < 42.0.2 Affected: >= 43.0.0, < 44.0.1

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-34945

Vulnerability from fkie_nvd - Published: 2026-04-09 19:16 - Updated: 2026-04-09 19:16

Severity ?

2.3 (Low) - 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

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "cveTags": [],
  "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\u0027s 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\u0027s stack to WebAssembly guests. The host\u0027s 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\u0027s index type to see how large the returned register could be. When combined with details about Wnich\u0027s 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."
    }
  ],
  "id": "CVE-2026-34945",
  "lastModified": "2026-04-09T19:16:24.330",
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          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
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rustsec-2026-0086

Vulnerability from osv_rustsec

Published

2026-04-09 12:00

Modified

2026-04-09 19:59

Summary

Host data leakage with 64-bit tables and Winch

Details

This is an entry in the RustSec database for the Wasmtime security advisory located at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946 For more information see the GitHub-hosted security advisory.

Severity

2.3 (Low)


                    
                      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

References

URL

Type

	https://crates.io/crates/wasmtime	PACKAGE
	https://rustsec.org/advisories/RUSTSEC-2026-0086.html	ADVISORY
	https://github.com/bytecodealliance/wasmtime/secu…	ADVISORY

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "categories": [],
        "cvss": "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",
        "informational": null
      },
      "ecosystem_specific": {
        "affected_functions": null,
        "affects": {
          "arch": [],
          "functions": [],
          "os": []
        }
      },
      "package": {
        "ecosystem": "crates.io",
        "name": "wasmtime",
        "purl": "pkg:cargo/wasmtime"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.0.0-0"
            },
            {
              "fixed": "36.0.7"
            },
            {
              "introduced": "37.0.0"
            },
            {
              "fixed": "42.0.2"
            },
            {
              "introduced": "43.0.0"
            },
            {
              "fixed": "43.0.1"
            }
          ],
          "type": "SEMVER"
        }
      ],
      "versions": []
    }
  ],
  "aliases": [
    "CVE-2026-34945",
    "GHSA-m9w2-8782-2946"
  ],
  "database_specific": {
    "license": "CC0-1.0"
  },
  "details": "This is an entry in the RustSec database for the Wasmtime security advisory\nlocated at\nhttps://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946\nFor more information see the GitHub-hosted security advisory.",
  "id": "RUSTSEC-2026-0086",
  "modified": "2026-04-09T19:59:38Z",
  "published": "2026-04-09T12:00:00Z",
  "references": [
    {
      "type": "PACKAGE",
      "url": "https://crates.io/crates/wasmtime"
    },
    {
      "type": "ADVISORY",
      "url": "https://rustsec.org/advisories/RUSTSEC-2026-0086.html"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946"
    }
  ],
  "related": [],
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Host data leakage with 64-bit tables and Winch"
}

GHSA-M9W2-8782-2946

Vulnerability from github – Published: 2026-04-09 20:23 – Updated: 2026-04-10 14:39

Summary

Wasmtime has host data leakage with 64-bit tables and Winch

Details

Impact

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 information disclosure should not be possible in WebAssembly, violates spec semantics, and is a vulnerability in Wasmtime.

Patches

Wasmtime 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.

Workarounds

Users of Cranelift are not affected by this issue, but users of Winch have no workarounds other than disabling the Config::wasm_memory64 proposal.

Severity ?

2.3 (Low)


                  
                    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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "wasmtime"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "25.0.0"
            },
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      ]
    },
    {
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        "ecosystem": "crates.io",
        "name": "wasmtime"
      },
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        {
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        }
      ],
      "versions": [
        "43.0.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-34945"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-200",
      "CWE-681"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-09T20:23:02Z",
    "nvd_published_at": "2026-04-09T19:16:24Z",
    "severity": "LOW"
  },
  "details": "### Impact\n\nWasmtime\u0027s 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\u0027s stack to WebAssembly guests. The host\u0027s stack can possibly contain sensitive data related to other host-originating operations which is not intended to be disclosed to guests.\n\nThis 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\u0027s index type to see how large the returned register could be. When combined with details about Wnich\u0027s ABI, such as multi-value returns, this can be combined to read stack data from the host, within a guest. This information disclosure should not be possible in WebAssembly, violates spec semantics, and is a vulnerability in Wasmtime.\n\n### Patches\n\nWasmtime 36.0.7, 42.0.2, and 43.0.1 have been issued to fix this bug. Users are recommended to update to these patched versions of Wasmtime.\n\n### Workarounds\n\nUsers of Cranelift are not affected by this issue, but users of Winch have no workarounds other than disabling the `Config::wasm_memory64` proposal.",
  "id": "GHSA-m9w2-8782-2946",
  "modified": "2026-04-10T14:39:23Z",
  "published": "2026-04-09T20:23:02Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-m9w2-8782-2946"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34945"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/bytecodealliance/wasmtime"
    },
    {
      "type": "WEB",
      "url": "https://rustsec.org/advisories/RUSTSEC-2026-0086.html"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Wasmtime has host data leakage with 64-bit tables and Winch"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-34945 (GCVE-0-2026-34945)

FKIE_CVE-2026-34945

rustsec-2026-0086

Vulnerability from osv_rustsec

GHSA-M9W2-8782-2946

Impact

Patches

Workarounds

Tags

Sightings

Nomenclature