CVE-2026-34983: Wasmtime is a runtime for WebAssembly

Routine

MEDIUM 5.0DOWNGRADE

CVE-2026-34983 is a medium-severity flaw (CVSS 5.0) 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. In 43.0.0, cloning a wasmtime::Linker is unsound and can result in use-after-free bugs. This bug is not controllable by guest Wasm programs. It can only be triggered by a specific sequence of embedder API calls made by the host. Specifically, the following steps must occur to trigger the bug clone a wasmtime::Linker, drop the original linker instance, use the new, cloned linker instance, resulting in a use-a

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.0 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	0.1% (top 98%)
CISA exploited list	No
Weakness	CWE-416
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 DOWNGRADE

Affected: 43.0.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 43.0.0

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 43.0.0 (Debian / Ubuntu)

apt-cache madison wasmtime sudo apt install wasmtime=<VERSION_BEFORE_43.0.0> sudo apt-mark hold wasmtime

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list wasmtime sudo dnf downgrade wasmtime-<VERSION_BEFORE_43.0.0> 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-2026-34983?

wasmtime: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-34983 being exploited?

CVE-2026-34983 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-2026-34983 affect?

CVE-2026-34983 affects wasmtime. Severity is medium (CVSS 5.0). Wasmtime is a runtime for WebAssembly. In 43.0.0, cloning a wasmtime::Linker is unsound and can result in use-after-free bugs. This bug is not controllable by guest Wasm programs. It can only be triggered by a specific sequence of embedder

How urgent is CVE-2026-34983?

Priority 18/100. No elevated risk signals yet.

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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