CVE-2026-34946: Wasmtime Wasmtime Has Host Panic When Vulnerability

MODERATE
Advisory Identifier: GHSA-q49f-xg75-m9xw
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CVSS 7.5
CWE-670 CWE-248
Published
Advisory Summary

CVE-2026-34946 is a MODERATE (CVSS 7.5) wasmtime has host panic when vulnerability (CWE-670: Always-Incorrect Control Flow Implementation) affecting Wasmtime libraries in the crates.io ecosystem. The issue involves wasmtime has host panic when winch compiler executes `table.fill`. Remediation is available by upgrading affected packages to version 36.0.7, 42.0.2, 43.0.1.

CVE-2026-34946 at a Glance

CVE Identifier CVE-2026-34946
GHSA Identifier GHSA-q49f-xg75-m9xw
Severity MODERATE
CVSS v3.1 Base Score 7.5
CWE Classification CWE-670: Always-Incorrect Control Flow Implementation
Affected Product Wasmtime
Package Ecosystem crates.io
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-34946

To remediate this vulnerability, upgrade all affected Wasmtime dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

wasmtime fixed: 36.0.7 
Upgrade wasmtime to 36.0.7
wasmtime fixed: 42.0.2 
Upgrade wasmtime to 42.0.2
wasmtime fixed: 43.0.1 
Upgrade wasmtime to 43.0.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for wasmtime

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-34946, inspect your project dependencies for Wasmtime:

inspect dependencies for wasmtime

Analyze the terminal output to locate any version of Wasmtime in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 36.0.7), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-670: Always-Incorrect Control Flow Implementation, where the code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated. In Wasmtime, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Wasmtime's Winch compiler contains a vulnerability where the compilation of the `table.fill` instruction can result in a host panic. This means that a valid guest can be compiled with Winch, on any architecture, and cause the host to panic. This represents a denial-of-service vulnerability in Wasmtime due to guests being able to trigger a panic. The specific issue is that a historical refactoring, #11254, changed how compiled code referenced tables within the `table.*` instructions. This refactoring forgot to update the Winch code paths associated as well, meaning that Winch was using the wrong indexing scheme. Due to the feature support of Winch the only problem that can result is tables being mixed up or nonexistent tables being used, meaning that the guest is limited to panicking the host (using a nonexistent table), or executing spec-incorrect behavior and modifying the wrong table. ### 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 for users of Winch there is no workaround for this bug. Hosts are recommended to updated to a patched version of Wasmtime.

CVE-2026-34946 Affected Wasmtime Versions

3 component(s)
Fixed Versions:
36.0.742.0.243.0.1
Product / Package Ecosystem Affected Versions Fixed Version
wasmtime
 crates.io
≥ 25.0.0
< 36.0.7
36.0.7
wasmtime
 crates.io
≥ 37.0.0
< 42.0.2
42.0.2
wasmtime
 crates.io
≥ 43.0.0
< 43.0.1
All 1 versions
43.0.0
43.0.1

References

GitHub Advisory / Wiki ADVISORY
https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-q49f-xg75-m9xw
NVD — CVE-2026-34946 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34946
Wasmtime Source Repository REPOSITORY
https://github.com/bytecodealliance/wasmtime
rustsec.org/advisories/rustsec-... WEB
https://rustsec.org/advisories/RUSTSEC-2026-0089.html

Frequently Asked Questions

What is CVE-2026-34946?
CVE-2026-34946 is a security vulnerability in Wasmtime involving Wasmtime has host panic when Winch compiler executes `table.fill` under CWE-670: Always-Incorrect Control Flow Implementation.
Which Wasmtime versions are affected?
Affected versions include releases prior to 36.0.7, 42.0.2, 43.0.1 across affected packages: wasmtime.
What version fixes CVE-2026-34946?
Upgrading to 36.0.7, 42.0.2, 43.0.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is wasmtime affected?
Yes, wasmtime is affected in releases prior to 36.0.7, 42.0.2, 43.0.1. Upgrade your dependency to 36.0.7, 42.0.2, 43.0.1 or later.
What is the CVSS score of CVE-2026-34946?
CVE-2026-34946 has a CVSS v3.1 base score of 7.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-34946?
CVE-2026-34946 is classified under CWE-670: Always-Incorrect Control Flow Implementation (The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated.).
How can I check crates.io dependencies for CVE-2026-34946?
Run the dependency tree command: 'inspect dependencies for wasmtime'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q49f-xg75-m9xw",
  "modified" : "2026-04-24T21:03:25Z",
  "published" : "2026-04-09T20:23:21Z",
  "aliases" : [ "CVE-2026-34946" ],
  "summary" : "Wasmtime has host panic when Winch compiler executes `table.fill`",
  "details" : "### Impact\n\nWasmtime's Winch compiler contains a vulnerability where the compilation of the `table.fill` instruction can result in a host panic. This means that a valid guest can be compiled with Winch, on any architecture, and cause the host to panic. This represents a denial-of-service vulnerability in Wasmtime due to guests being able to trigger a panic.\n\nThe specific issue is that a historical refactoring, #11254, changed how compiled code referenced tables within the `table.*` instructions. This refactoring forgot to update the Winch code paths associated as well, meaning that Winch was using the wrong indexing scheme. Due to the feature support of Winch the only problem that can result is tables being mixed up or nonexistent tables being used, meaning that the guest is limited to panicking the host (using a nonexistent table), or executing spec-incorrect behavior and modifying the wrong table.\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 for users of Winch there is no workaround for this bug. Hosts are recommended to updated to a patched version of Wasmtime.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "wasmtime"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "25.0.0"
      }, {
        "fixed" : "36.0.7"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "wasmtime"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "37.0.0"
      }, {
        "fixed" : "42.0.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "wasmtime"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "43.0.0"
      }, {
        "fixed" : "43.0.1"
      } ]
    } ],
    "versions" : [ "43.0.0" ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/bytecodealliance/wasmtime/security/advisories/GHSA-q49f-xg75-m9xw"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-34946"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/bytecodealliance/wasmtime"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2026-0089.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-248", "CWE-670" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-09T20:23:21Z",
    "nvd_published_at" : "2026-04-09T19:16:24Z"
  }
}