Bug 2489049 (CVE-2026-47261)

Summary: CVE-2026-47261 wasmtime-wasi: Wasmtime: Wasmtime: Access control bypass allows unauthorized file truncation via specific open flags.
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Wasmtime, a runtime for WebAssembly. This vulnerability allows an attacker to bypass intended access controls when a filesystem preopen is configured with read-only file permissions but also allows directory mutations. By using specific open flags, an attacker can truncate files that should not be writable, leading to unauthorized data modification. This issue affects wasmtime-wasi embeddings that combine directory mutation permissions with read-only file permissions.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2496795, 2496796    
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Description OSIDB Bzimport 2026-06-15 21:02:00 UTC 
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.