Vulnerability-Lookup

CVE-2026-34941 (GCVE-0-2026-34941)

Vulnerability from cvelistv5 – Published: 2026-04-09 18:29 – Updated: 2026-04-10 14:11

Title

Wasmtime has a Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding

Summary

Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, Wasmtime contains a vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units. This vulnerability can cause the host to read beyond the end of a WebAssembly's linear memory in an attempt to transcode nonexistent bytes. In Wasmtime's default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16. A host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1.

Severity ?

6.9 (Medium)


                        
                          CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CWE

CWE-125 - Out-of-bounds Read

Assigner

GitHub_M

References

URL

Tags

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

x_refsource_CONFIRM

Impacted products

	Vendor	Product	Version
	bytecodealliance	wasmtime	Affected: < 24.0.7 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-2026-34941

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

Severity ?

6.9 (Medium) - CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hx6p-xpx3-jvvv

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "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 vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units. This vulnerability can cause the host to read beyond the end of a WebAssembly\u0027s linear memory in an attempt to transcode nonexistent bytes. In Wasmtime\u0027s default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16. A host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled. This vulnerability is fixed in 24.0.7, 36.0.7, 42.0.2, and 43.0.1."
    }
  ],
  "id": "CVE-2026-34941",
  "lastModified": "2026-04-09T19:16:23.693",
  "metrics": {
    "cvssMetricV40": [
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        "cvssData": {
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          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
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          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 6.9,
          "baseSeverity": "MEDIUM",
          "confidentialityRequirement": "NOT_DEFINED",
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          "modifiedAttackComplexity": "NOT_DEFINED",
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          "modifiedAttackVector": "NOT_DEFINED",
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GHSA-HX6P-XPX3-JVVV

Vulnerability from github – Published: 2026-04-09 20:22 – Updated: 2026-04-10 14:41

Summary

Wasmtime: Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding

Details

Summary

Wasmtime contains a vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units.

This vulnerability can cause the host to read beyond the end of a WebAssembly's linear memory in an attempt to transcode nonexistent bytes. In Wasmtime's default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16.

A host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled.

Impact

This is an out-of-bounds memory access. Any user running untrusted wasm components that use cross-component string passing (with UTF-16 source and latin1+utf16 destination encodings) is affected.

With guard pages: Denial of service. The host process crashes with SIGBUS/SIGSEGV.
Without guard pages: Potential information disclosure. The guest can read host memory beyond its linear memory allocation.

Patches

Wasmtime 24.0.7, 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

There is no workaround for this bug. Hosts are recommended to updated to a patched version of Wasmtime.

Severity ?

6.9 (Medium)


                  
                    CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "wasmtime"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "24.0.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "wasmtime"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "25.0.0"
            },
            {
              "fixed": "36.0.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "wasmtime"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "37.0.0"
            },
            {
              "fixed": "42.0.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "wasmtime"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "43.0.0"
            },
            {
              "fixed": "43.0.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "43.0.0"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-34941"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-125"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-09T20:22:08Z",
    "nvd_published_at": "2026-04-09T19:16:23Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nWasmtime contains a vulnerability where when transcoding a UTF-16 string to the latin1+utf16 component-model encoding it would incorrectly validate the byte length of the input string when performing a bounds check. Specifically the number of code units were checked instead of the byte length, which is twice the size of the code units.\n\nThis vulnerability can cause the host to read beyond the end of a WebAssembly\u0027s linear memory in an attempt to transcode nonexistent bytes. In Wasmtime\u0027s default configuration this will read unmapped memory on a guard page, terminating the process with a segfault. Wasmtime can be configured, however, without guard pages which would mean that host memory beyond the end of linear memory may be read and interpreted as UTF-16.\n\nA host segfault is a denial-of-service vulnerability in Wasmtime, and possibly being able to read beyond the end of linear memory is additionally a vulnerability. Note that reading beyond the end of linear memory requires nonstandard configuration of Wasmtime, specifically with guard pages disabled.\n\n### Impact\n\nThis is an out-of-bounds memory access. Any user running untrusted wasm components that use cross-component string passing (with UTF-16 source and latin1+utf16 destination encodings) is affected.\n\n- With guard pages: Denial of service. The host process crashes with SIGBUS/SIGSEGV.\n- Without guard pages: Potential information disclosure. The guest can read host memory beyond its linear memory allocation.\n\nPatches\n\nWasmtime 24.0.7, 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.\nWorkarounds\n\nThere is no workaround for this bug. Hosts are recommended to updated to a patched version of Wasmtime.",
  "id": "GHSA-hx6p-xpx3-jvvv",
  "modified": "2026-04-10T14:41:09Z",
  "published": "2026-04-09T20:22:08Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hx6p-xpx3-jvvv"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34941"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/bytecodealliance/wasmtime"
    },
    {
      "type": "WEB",
      "url": "https://rustsec.org/advisories/RUSTSEC-2026-0093.html"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Wasmtime: Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding"
}

rustsec-2026-0093

Vulnerability from osv_rustsec

Published

2026-04-09 12:00

Modified

2026-04-09 19:59

Summary

Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding

Details

This is an entry in the RustSec database for the Wasmtime security advisory located at https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hx6p-xpx3-jvvv For more information see the GitHub-hosted security advisory.

Severity

6.9 (Medium)


                    
                      CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

References

URL

Type

	https://crates.io/crates/wasmtime	PACKAGE
	https://rustsec.org/advisories/RUSTSEC-2026-0093.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:N/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/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": "24.0.7"
            },
            {
              "introduced": "25.0.0"
            },
            {
              "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-2026-34941",
    "GHSA-hx6p-xpx3-jvvv"
  ],
  "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-hx6p-xpx3-jvvv\nFor more information see the GitHub-hosted security advisory.",
  "id": "RUSTSEC-2026-0093",
  "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-2026-0093.html"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-hx6p-xpx3-jvvv"
    }
  ],
  "related": [],
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Heap OOB read in component model UTF-16 to latin1+utf16 string transcoding"
}

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-2026-34941 (GCVE-0-2026-34941)

FKIE_CVE-2026-34941

GHSA-HX6P-XPX3-JVVV

Summary

Impact

rustsec-2026-0093

Vulnerability from osv_rustsec

Tags

Sightings

Nomenclature