WasmtimeApplication · Bytecodealliance
CVE-2026-54786
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 · uneditedWasmtime is a runtime for WebAssembly. All versions prior to 24.0.10; versions 25.0.0 through those before 36.0.11; versions 37.0.0 through those before 44.0.3; and versions 45.0.0 and 45.0.1 contain a native implementation of WASIp1 which suffers from a leak in the fd_renumber function where the file descriptor being renumbered to is not properly closed. Wasmtime's implementation erroneously only updated the table of descriptors for WASIp1 and didn't update the underlying table of descriptors used by the host. This behavior means that while fd_renumber works correctly from a guest's perspective it ends up leaking resources in the host that aren't cleaned up until the corresponding Store is destroyed. In a loop, guests can use fd_renumber to cause hosts to exhaust both resources and file descriptors. This bug only affects the native implementation of WASIp1, meaning that only runtimes which load core wasm modules and expose fd_renumber are affected. Runtimes are additionally only affected if they expose the ability to acquire a file descriptor, such as opening a file. For runtimes that deny access to files they are unaffected. This issue has been fixed in versions 24.0.10, 36.0.11, 44.0.3, and 45.0.2.
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 confidenceThe fd_renumber function in Wasmtime's native WASIp1 implementation fails to close the destination file descriptor before remapping, causing the underlying host descriptor table to retain leaked references while only updating the WASIp1 guest-visible table. This creates a resource leak where file descriptors accumulate on the host side until the Store is destroyed.
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
< 24.0.10>= 25.0.0, < 36.0.11>= 37.0.0, < 44.0.3>= 45.0.0, < 45.0.2CVSS 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
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- None
- Integrity
- None
- Availability
- Low
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:L
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 checksWork through these to decide whether this CVE applies to you.
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Check Wasmtime versionRun 'wasmtime --version' or inspect the Wasmtime library version in your dependency manifestAffected if The installed version is < 24.0.10, or >= 25.0.0 and < 36.0.11, or >= 37.0.0 and < 44.0.3, or >= 45.0.0 and < 45.0.2
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Verify WASIp1 is enabledInspect the Wasmtime configuration or runtime flags used to launch your WASI module; look for WASIp1 (wasi_snapshot_preview1) context or similarAffected if Your Wasmtime runtime is configured to provide WASIp1 support to guest modules
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Confirm file descriptor operations are usedReview your guest WebAssembly module code or runtime logs for calls that trigger fd_renumber, such as fd_renumber, file descriptor duplication, or similar WASI file operationsAffected if Guest code performs file descriptor renaming or duplication operations via WASI APIs
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Monitor for file descriptor accumulationObserve the process file descriptor count over time while running WASIp1 workloads; on Linux this can be done with 'ls -la /proc/<pid>/fd | wc -l'Affected if File descriptors accumulate continuously without being released during WASI file operations
You are affected if your Wasmtime version falls within the affected ranges AND you run guest modules that use WASIp1 with file descriptor operations.
Generated from the published advisory. Verify against your own configuration.
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 · scoped24.0.1036.0.1144.0.3
Upgrade Wasmtime to versions 24.0.10, 36.0.11, 44.0.3, or 45.0.2 or later. For runtimes that cannot upgrade, deny untrusted guests access to file operations to eliminate the attack surface.
Upgrade to 24.0.10, 36.0.11, 44.0.3, or 45.0.2 (depending on your current version branch) - prefer the latest stable release in your version line
- 1. Identify the current Wasmtime version in use by checking your project's dependencies or runtime configuration
- 2. Based on your current version, upgrade to the appropriate fixed release: if < 24.0.10 upgrade to 24.0.10 or later; if 25.0.0-36.x upgrade to 36.0.11 or later; if 37.0.0-44.x upgrade to 44.0.3 or later; if 45.0.0-45.0.1 upgrade to 45.0.2 or later
- 3. Update the Wasmtime dependency in your Cargo.toml, lock file, or package manager configuration to the relevant fixed version
- 4. Rebuild and test your application to ensure the upgrade does not break existing functionality
- 5. If your runtime exposes file descriptor access to WebAssembly guests, verify that fd_renumber now properly closes the source file descriptor
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Wasmtime
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,808.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-54786 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-54786 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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