CVE-2026-34943: Wasmtime is a runtime for WebAssembly

Routine

HIGH 7.5REMOTEUPGRADE

CVE-2026-34943 is a high-severity flaw (CVSS 7.5) affecting wasmtime. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, 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

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 75%)
CISA exploited list	No
Weakness	CWE-248
Published	2026-04-09
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: bytecodealliance

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-09 19:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

bytecodealliance wasmtime UPGRADE

Affected: < 24.0.7 · >= 25.0.0 and < 36.0.7 · >= 37.0.0 and < 42.0.2 · >= 43.0.0 and < 43.0.1

Fixed in: 24.0.7, 36.0.7, 42.0.2, 43.0.1

Safe to downgrade to: a release before 25.0.0

1. Check installed version

apt-cache policy wasmtime || rpm -q wasmtime || wasmtime --version

2. UPGRADE to 24.0.7 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade wasmtime

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade wasmtime

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 25.0.0 (Debian / Ubuntu)

apt-cache madison wasmtime sudo apt install wasmtime=<VERSION_BEFORE_25.0.0> sudo apt-mark hold wasmtime

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list wasmtime sudo dnf downgrade wasmtime-<VERSION_BEFORE_25.0.0> sudo dnf versionlock add wasmtime

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-34943?

wasmtime: upgrade to 24.0.7, 36.0.7, 42.0.2, 43.0.1. Exact commands for each OS are on this page.

Is CVE-2026-34943 being exploited?

CVE-2026-34943 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-34943 affect?

CVE-2026-34943 affects wasmtime. Severity is high (CVSS 7.5). Wasmtime is a runtime for WebAssembly. Prior to 24.0.7, 36.0.7, 42.0.2, and 43.0.1, 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

How urgent is CVE-2026-34943?

Priority 38/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-34987 CRITICAL 9.9 UPGRADE Wasmtime is a runtime for WebAssembly
CVE-2026-34946 HIGH 7.5 UPGRADE Wasmtime is a runtime for WebAssembly
CVE-2026-35186 HIGH 7.5 UPGRADE Wasmtime is a runtime for WebAssembly
CVE-2026-34971 HIGH 7.8 UPGRADE Wasmtime is a runtime for WebAssembly
CVE-2026-34945 MEDIUM 6.5 UPGRADE Wasmtime is a runtime for WebAssembly

References

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