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Fencer Vulns
high 7.5

CVE-2026-35186 json

Wasmtime has an improperly masked return value from `table.grow` with Winch compiler backend

published 2026-04-09 7 mo ago modified 2026-10-26 13 d ago also EUVD-2026-21037 , GHSA-f984-pcp8-v2p7 , JLSEC-2026-1363 , RUSTSEC-2026-0094

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 12%
public exploits
0
none known

Summary

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 backend contains a bug where translating the table.grow operator causes the result to be incorrectly typed. For 32-bit tables this means that the result of the operator, internally in Winch, is tagged as a 64-bit value instead of a 32-bit value. This invalid internal representation of Winch's compiler state compounds into further issues depending on how the value is consumed. The primary consequence of this bug is that bytes in the host's address space can be stored/read from. This is only applicable to the 16 bytes before linear memory, however, as the only significant return value of table.grow that can be misinterpreted is -1. The bytes before linear memory are, by default, unmapped memory. Wasmtime will detect this fault and abort the process, however, because wasm should not be able to access these bytes. Overall this this bug in Winch represents a DoS vector by crashing the host process, a correctness issue within Winch, and a possible leak of up to 16-bytes before linear memory. Wasmtime's default compiler is Cranelift, not Winch, and Wasmtime's default settings are to place guard pages before linear memory. This means that Wasmtime's default configuration is not affected by this issue, and when explicitly choosing Winch Wasmtime's otherwise default configuration leads to a DoS. Disabling guard pages before linear memory is required to possibly leak up to 16-bytes of host data. This vulnerability is fixed in 36.0.7, 42.0.2, and 43.0.1.

Patch / fix

  • crates.io wasmtime 36.0.7, 42.0.2, 43.0.1
  • julia Wasmtime_jll 45.0.1+0
  • bytecodealliance wasmtime 36.0.7, 42.0.2, 44.0.1
  • rust-wasmtime Debian 14 36.0.7+dfsg-1

debian advisories DEBIAN-CVE-2026-35186

  • tree-sitter openSUSE Tumbleweed 0.26.8-2.1

opensuse advisories openSUSE-SU-2026:10715-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-35186 updated cvss 6.9

Wasmtime: github.com/bytecodealliance/wasmtime: Wasmtime: Denial of Service and potential information disclosure via Winch compiler type confusion

  • Red Hat Connectivity Link 1 redhat-user-workloads/api-management-tenant/rhcl-1-3-wasm-shim Red Hat Enterprise Linux 10 virt-firmware-rs
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
6 mo ago

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 6.1 CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
CISA ADP 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA 4.0 6.1 CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:L/VA:H/SC:N/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
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
crates.io wasmtime
>=25.0.0, <36.0.7
>=37.0.0, <42.0.2
>=43.0.0, <43.0.1
>=0.0.0-0, <36.0.7
36.0.7
42.0.2
43.0.1
julia Wasmtime_jll
>=39.0.0+0, <45.0.1+0
45.0.1+0

Affected products

  • bytecodealliance wasmtime

Classification

Weakness
  • CWE-789 Memory Allocation with Excessive Size Value

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.