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VulnerabilityPublished Updated

CVE-2026-34983: bytecodealliance wasmtime · Use After Free

Affects bytecodealliance wasmtimeSource CVE Database V5

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Not known to be exploited · CVSS 1.0 Low : upgrade to 43.0.1 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score
1.0Low
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.1% chance of exploitation in 30 days – higher than 1% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 43.0.1
CVSS:4.0/AV:P/AC:H/AT:P/PR:H/UI:A/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 9 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade wasmtime and github/bytecodealliance/wasmtime to 43.0.1.

Affected software

ProductAffectedFixed in
bytecodealliancewasmtimeAffected
  • >=43.0.0 <43.0.1
Fixed in
  • 43.0.1
crates.iogithub/bytecodealliance/wasmtimepkg:cargo/github/bytecodealliance/wasmtimeOther threatsAffected
  • <43.0.1
Fixed in
  • 43.0.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade to wasmtime version 43.0.1 or later, where this use-after-free vulnerability is fixed. Since this is a library-level bug triggered by host API misuse, applying the official patch is the recommended remediation.

Description

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-after-free. This vulnerability is fixed in 43.0.1.

References

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