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CVE-2026-34945· NVD / CVE Program· CNA GitHub_M

Wasmtime leaks host data with 64-bit tables and Winch

Wasmtime is a runtime for WebAssembly. From 25.0.0 to before 36.0.7, 42.0.2, and 43.0.1, 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 vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.

LowCVSS 2.3 · v4.0—No exploit Fix available
Published
Apr 9, 2026
Updated
Jun 17, 2026
EPSS
0.4% · 30th percentile
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Report tools

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Action score

9

Monitor

Low priority for now.

CVSS
9 / 40 · 2.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.4%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · GitHub_M
2.3
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for the hundreds of thousands of vulnerabilities in the database; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

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Affected systems

VendorProduct
bytecodealliancewasmtime

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • bytecodealliance wasmtime25.0.0 and later · before 36.0.7
  • bytecodealliance wasmtime37.0.0 and later · before 42.0.2
  • bytecodealliance wasmtime43.0.0 and later · before 43.0.1

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • bytecodealliance wasmtime

    • >= 25.0.0, < 36.0.7, >= 37.0.0, < 42.0.2, >= 43.0.0, < 44.0.1affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
crates.iowasmtimefrom 0.0.0-0 · before 36.0.736.0.7
crates.iowasmtimefrom 25.0.0 · before 36.0.736.0.7
crates.iowasmtimefrom 37.0.0 · before 42.0.242.0.2
crates.iowasmtimefrom 43.0.0 · before 43.0.143.0.1
Debian:13rust-wasmtimeall versions—
Debian:14rust-wasmtimebefore 36.0.7+dfsg-136.0.7+dfsg-1
openSUSE:Tumbleweedtree-sitterbefore 0.26.8-1.10.26.8-1.1

Same product

bytecodealliance: all records

Other highest-scoring records for the same primary product.

  • CVE-2022-39394wasmtime_trap_code C API function has out of bounds write vulnerability
    39Monitor
  • CVE-2022-24791Use after free in Wasmtime
    39Monitor
  • CVE-2026-34987Wasmtime with Winch compiler backend on aarch64 may allow a sandbox-escaping memory access
    36Monitor
  • CVE-2026-34971Wasmtime miscompiled guest heap access enables sandbox escape on aarch64 Cranelift
    36Monitor
  • CVE-2023-30624Wasmtime has Undefined Behavior in Rust runtime functions
    35Monitor
  • CVE-2022-39393Wasmtime vulnerable to data leakage between instances in the pooling allocator
    34Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
bytecodealliance wasmtime36.0.7 · descriptionVendor (CNA)
crates.io:wasmtime36.0.7Package registry (OSV)
crates.io:wasmtime42.0.2Package registry (OSV)
crates.io:wasmtime43.0.1Package registry (OSV)
debian:rust-wasmtime36.0.7+dfsg-1 · Debian:14Package registry (OSV)
opensuse:tree-sitter0.26.8-1.1 · openSUSE:TumbleweedPackage registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
X

Weakness class (CWE)

CWE-681 · Incorrect Conversion between Numeric Types

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records