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Fencer Vulns
high 7.5

CVE-2026-47261 json

Wasmtime: WASI path_open(TRUNCATE) bypasses `FilePerms::WRITE` host restriction

published 2026-05-21 5 mo ago modified 2026-10-25 14 d ago also EUVD-2026-37001 , GHSA-2r75-cxrj-cmph , JLSEC-2026-1366 , RUSTSEC-2026-0149

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 29%
public exploits
0
none known

Summary

Wasmtime is a runtime for WebAssembly. In versions prior to 24.0.9, 36.0.10, and 44.0.2, when a filesystem preopen is given DirPerms::all() and FilePerms::READ without FilePerms::WRITE, this access control mechanism can be bypassed via the wasip2 descriptor.open-at or wasip1 path_open interfaces by opening a file with only the OpenFlags::TRUNCATE oflag. The root cause is that the clause handling OpenFlags::TRUNCATE in crates/wasi/src/filesystem.rs (Dir::open_at, lines 967–969) did not set open_mode |= OpenMode::WRITE;, which is later used for the access control check against FilePerms to determine whether opening the file is permitted; the single-line fix adds that missing assignment, after which the affected calls correctly fail with error-code.not-permitted and ERRNO_PERM respectively. Only wasmtime-wasi embeddings that combine DirPerms::MUTATE with FilePerms::READ are affected by this bug. In particular, the Wasmtime project's wasmtime-cli's use of wasmtime-wasi is not affected, because it always sets FilePerms::all() for all preopens. This issue has been fixed in versions 24.0.9, 36.0.10 and44.0.2.

Patch / fix

  • crates.io wasmtime-wasi 24.0.9, 36.0.10, 44.0.2, 45.0.0
  • julia Wasmtime_jll 45.0.1+0
  • bytecodealliance wasmtime 24.0.9, 36.0.10, 44.0.2
  • rust-wasmtime Debian 14 36.0.11+dfsg-1

debian advisories DEBIAN-CVE-2026-47261

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-2026-47261 updated cvss 5.5

wasmtime-wasi: Wasmtime: Wasmtime: Access control bypass allows unauthorized file truncation via specific open flags.

  • Red Hat Connectivity Link 1 rhcl-1/wasm-shim-rhel9 Red Hat Enterprise Linux 10 virt-firmware-rs
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Hardened Images rust 1.96.0-4.hum1
    not affected: vulnerable code not present

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
4 mo ago

Exploit prediction

0.36% chance of exploitation in the next 30 days, higher than 29% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
GitHub 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
crates.io wasmtime-wasi
>=37.0.0, <44.0.2
>=25.0.0, <36.0.10
<24.0.9
>=0.0.0-0, <24.0.9
>=45.0.0, <45.0.0
44.0.2
36.0.10
24.0.9
45.0.0
julia Wasmtime_jll
<45.0.1+0
45.0.1+0

Affected products

  • bytecodealliance wasmtime

Classification

Weakness

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.