dbcve.org
WasmtimeApplication · Bytecodealliance

CVE-2026-47261

HIGH · 7.5 CVSS v3.1 Published 2026-06-15
Fix available
A fix is available. Upgrade to 24.0.9 / 36.0.10 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In Wasmtime versions prior to 24.0.9, 36.0.10, and 44.0.2, the filesystem preopen access control can be bypassed when DirPerms::MUTATE is combined with FilePerms::READ (without FilePerms::WRITE). Opening a file with OpenFlags::TRUNCATE via wasip2 descriptor.open-at or wasip1 path_open bypasses the permission check because the code path handling TRUNCATE doesn't set OpenMode::WRITE, which is required for the access control validation.

MitigationUpgrade Wasmtime to version 24.0.9, 36.0.10, or 44.0.2, or audit preopen configurations to ensure DirPerms::MUTATE is not combined with FilePerms::READ alone.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
WasmtimeApplication
Affected:< 24.0.9>= 25.0.0, < 36.0.10>= 37.0.0, < 44.0.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Wasmtime version
    Run 'wasmtime --version' or check the Cargo.toml dependency version if Wasmtime is embedded as a crate
    Affected if Version is < 24.0.9, or >= 25.0.0 and < 36.0.10, or >= 37.0.0 and < 44.0.2
  2. Confirm WASI filesystem preopen is in use
    Review the Wasmtime configuration or the WASI command-line arguments used when running the WebAssembly module. Look for --dir or preopen directories in the runtime setup
    Affected if Filesystem directories are preopened to the WASI module
  3. Check preopen permission configuration
    Examine the Wasmtime config code or command line for how DirPerms and FilePerms are set on preopened directories. Look for DirPerms::MUTATE combined with FilePerms::READ (without FilePerms::WRITE)
    Affected if The preopen grants DirPerms::MUTATE and FilePerms::READ but NOT FilePerms::WRITE
  4. Inspect for TRUNCATE file opens
    Review application source code or runtime logs to determine if any wasip2 descriptor.open-at or wasip1 path_open calls use OpenFlags::TRUNCATE on the affected preopened files
    Affected if The WASI application opens files with OpenFlags::TRUNCATE on preopened directories that lack FilePerms::WRITE

All four conditions must be true for the environment to be vulnerable: an affected Wasmtime version, WASI filesystem preopen in use, DirPerms::MUTATE with FilePerms::READ only, and files opened with TRUNCATE flag

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 24.0.9 / 36.0.10 / 44.0.2 or later
Fixed in 24.0.936.0.1044.0.2
Interim mitigation

Upgrade Wasmtime to version 24.0.9, 36.0.10, or 44.0.2, or audit preopen configurations to ensure DirPerms::MUTATE is not combined with FilePerms::READ alone.

Recommended fix High confidence

44.0.2 (or latest stable)

  1. Upgrade Wasmtime to version 24.0.9, 36.0.10, or 44.0.2 or later to resolve the access control bypass vulnerability

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Wasmtime Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA2.0 h
8.0 hours of engineering $1,390
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-47261 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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