CVE-2026-34943Network attack vector

Host process crash via invalid component flags

Published Apr 9, 2026 · Updated Apr 9, 2026

Uncaught exception in Bytecode Alliance Wasmtime affected releases allows attackers to crash a host process through a guest component. When wasmtime::component::Val lifts a flags-typed WIT value, it panics on out-of-range bits instead of ignoring those bits as specified. Reachability requires a host to use that Val lifting path for component-model flags; the panic terminates the host process and interrupts its service.

CVSS severity5.6
Medium
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncaught exception in Bytecode Alliance Wasmtime affected releases allows attackers to crash a host process through a guest component. When wasmtime::component::Val lifts a flags-typed WIT value, it panics on out-of-range bits instead of ignoring those bits as specified. Reachability requires a host to use that Val lifting path for component-model flags; the panic terminates the host process and interrupts its service.

The record

CVE
CVE-2026-34943
Published
Apr 9, 2026
Updated
Apr 9, 2026
Vendor
Bytecode Alliance
Product
Wasmtime
Classifications
CWE-248, T1499.004
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Apr 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 24.0.7
  2. Affected versionversion=>= 25.0.0, < 36.0.7
  3. Affected versionversion=>= 37.0.0, < 42.0.2
  4. Affected versionversion=>= 43.0.0, < 44.0.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Bytecode Alliance · Wasmtimeversion=< 24.0.7; version=>= 25.0.0, < 36.0.7; version=>= 37.0.0, < 42.0.2; version=>= 43.0.0, < 44.0.1

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.6GitHub, Inc.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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-248Uncaught Exception
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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