CVE-2026-34943: Wasmtime Wasmtime Has A Possible Panic Vulnerability

MODERATE
Advisory Identifier: GHSA-m758-wjhj-p3jq
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CVSS 7.5
CWE-248
Published
Advisory Summary

CVE-2026-34943 is a MODERATE (CVSS 7.5) wasmtime has a possible panic vulnerability (CWE-248: Uncaught Exception) affecting Wasmtime libraries in the crates.io ecosystem. The issue involves wasmtime has a possible panic when lifting `flags` component value. Remediation is available by upgrading affected packages to version 24.0.7, 36.0.7, 42.0.2, 43.0.1.

CVE-2026-34943 at a Glance

CVE Identifier CVE-2026-34943
GHSA Identifier GHSA-m758-wjhj-p3jq
Severity MODERATE
CVSS v3.1 Base Score 7.5
CWE Classification CWE-248: Uncaught Exception
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-2026-34943

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: 24.0.7 
Upgrade wasmtime to 24.0.7
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-2026-34943, 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 24.0.7), 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-248: Uncaught Exception, where an exception is thrown from a function, but it is not caught. 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 contains a possible panic which can happen when a `flags`-typed component model value is lifted with the `Val` type. If bits are set outside of the set of flags the component model specifies that these bits should be ignored but Wasmtime will panic when this value is lifted. This panic only affects wasmtime's implementation of lifting into `Val`, not when using the `flags!` macro. This additionally only affects `flags`-typed values which are part of a WIT interface. This has the risk of being a guest-controlled panic within the host which Wasmtime considers a DoS vector. ### 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 if a host meets the criteria to be affected. To be affected a host must be using `wasmtime::component::Val` and possibly work with a `flags` type in the component model.

CVE-2026-34943 Affected Wasmtime Versions

4 component(s)
Fixed Versions:
24.0.736.0.742.0.243.0.1
Product / Package Ecosystem Affected Versions Fixed Version
wasmtime
 crates.io
< 24.0.7
24.0.7
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-m758-wjhj-p3jq
NVD — CVE-2026-34943 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34943
Wasmtime Source Repository REPOSITORY
https://github.com/bytecodealliance/wasmtime
rustsec.org/advisories/rustsec-... WEB
https://rustsec.org/advisories/RUSTSEC-2026-0085.html

Frequently Asked Questions

What is CVE-2026-34943?
CVE-2026-34943 is a security vulnerability in Wasmtime involving Wasmtime has a possible panic when lifting `flags` component value under CWE-248: Uncaught Exception.
Which Wasmtime versions are affected?
Affected versions include releases prior to 24.0.7, 36.0.7, 42.0.2, 43.0.1 across affected packages: wasmtime.
What version fixes CVE-2026-34943?
Upgrading to 24.0.7, 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 24.0.7, 36.0.7, 42.0.2, 43.0.1. Upgrade your dependency to 24.0.7, 36.0.7, 42.0.2, 43.0.1 or later.
What is the CVSS score of CVE-2026-34943?
CVE-2026-34943 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-2026-34943?
CVE-2026-34943 is classified under CWE-248: Uncaught Exception (An exception is thrown from a function, but it is not caught.).
How can I check crates.io dependencies for CVE-2026-34943?
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-m758-wjhj-p3jq",
  "modified" : "2026-04-24T21:03:43Z",
  "published" : "2026-04-09T20:22:34Z",
  "aliases" : [ "CVE-2026-34943" ],
  "summary" : "Wasmtime has a possible panic when lifting `flags` component value",
  "details" : "### Impact\n\nWasmtime contains a possible panic which can happen when a `flags`-typed component model value is lifted with the `Val` type. If bits are set outside of the set of flags the component model specifies that these bits should be ignored but Wasmtime will panic when this value is lifted. This panic only affects wasmtime's implementation of lifting into `Val`, not when using the `flags!` macro. This additionally only affects `flags`-typed values which are part of a WIT interface. \n\nThis has the risk of being a guest-controlled panic within the host which Wasmtime considers a DoS vector.\n\n### Patches\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.\n\n### Workarounds\n\nThere is no workaround for this bug if a host meets the criteria to be affected. To be affected a host must be using `wasmtime::component::Val` and possibly work with a `flags` type in the component model.",
  "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:H/AT:P/PR:H/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "wasmtime"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "24.0.7"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "wasmtime"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "25.0.0"
      }, {
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      } ]
    } ]
  }, {
    "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-m758-wjhj-p3jq"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-34943"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/bytecodealliance/wasmtime"
  }, {
    "type" : "WEB",
    "url" : "https://rustsec.org/advisories/RUSTSEC-2026-0085.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-248" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-09T20:22:34Z",
    "nvd_published_at" : "2026-04-09T19:16:24Z"
  }
}