How severe is CVE-2026-34945?

No CVSS score has been assigned to CVE-2026-34945 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-34945?

CVE-2026-34945 affects the following packages: wasmtime (crates.io), wasmtime (crates.io), wasmtime (crates.io). Ecosystems affected: crates.io.

How do I fix CVE-2026-34945?

Update wasmtime to 36.0.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34945 is resolved across your whole dependency graph.

How do I detect CVE-2026-34945 in my crates.io dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for wasmtime, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-34945 if there is no patch (or I can't update yet)?

Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Is CVE-2026-34945 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-34945 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-34945?

CVE-2026-34945 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 25th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-34945?

CVE-2026-34945 is classified as CWE-681 (CWE-681). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-34945 published, and has it been updated?

CVE-2026-34945 was published on April 9, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🦀 crates.io

Not in CISA KEV

CVE-2026-34945 — wasmtime

CVE-2026-34945 is a CWE-681 vulnerability in wasmtime. A fix is available for wasmtime — see the affected versions and patch details below.

Wasmtime leaks host data with 64-bit tables and Winch

Also known asGHSA-m9w2-8782-2946RUSTSEC-2026-0086

Published

Apr 9, 2026

Updated

Oct 28, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-34945.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs25th percentile — riskier than 25% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

3 pkgs affected

🦀wasmtime🦀wasmtime🦀wasmtime

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.

Description

Impact

Wasmtime's Winch compiler contains a bug where a 64-bit table, part of the memory64 proposal of WebAssembly, incorrectly translated the table.size instruction. This bug could lead to disclosing data on the host's stack to WebAssembly guests. The host's stack can possibly contain sensitive data related to other host-originating operations which is not intended to be disclosed to guests.

This bug specifically arose from a mistake where the return value of table.size was statically typed as a 32-bit integer, as opposed to consulting the table's index type to see how large the returned register could be. When combined with details about Wnich's ABI, such as multi-value returns, this can be combined to read stack data from the host, within a guest. This information disclosure should not be possible in WebAssembly, violates spec semantics, and is a vulnerability in Wasmtime.

Patches

Wasmtime 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

Users of Cranelift are not affected by this issue, but users of Winch have no workarounds other than disabling the Config::wasm_memory64 proposal.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
🦀crates.io	`wasmtime`	≥ 25.0.0&&< 36.0.7	36.0.7`cargo update -p wasmtime --precise 36.0.7`
🦀crates.io	`wasmtime`	≥ 37.0.0&&< 42.0.2	42.0.2`cargo update -p wasmtime --precise 42.0.2`
🦀crates.io	`wasmtime`	≥ 43.0.0&&< 43.0.1	43.0.1`cargo update -p wasmtime --precise 43.0.1`

Affected Products

1 product · 3 configurations

Application

wasmtimebytecodealliance

≥ 43.0.0 && < 43.0.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for wasmtime, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update wasmtime to 36.0.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34945 is resolved across your whole dependency graph.
Workarounds
Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-34945 (CC BY 4.0)

Frequently Asked Questions

### Impact Wasmtime's Winch compiler contains a bug where a 64-bit table, part of the memory64 proposal of WebAssembly, incorrectly translated the `table.size` instruction. This bug could lead to disclosing data on the host's stack to WebAssembly guests. The host's stack can possibly contain sensitive data related to other host-originating operations which is not intended to be disclosed to guests. This bug specifically arose from a mistake where the return value of `table.size` was statically typed as a 32-bit integer, as opposed to consulting the table's index type to see how large the ret

O3 Security · Impact-Aware SCA

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