Wasmtime EUVD-2026-108313

Requires ALL of: a Unix host (Windows is explicitly unaffected because its system-specific conversion handles pre-epoch times correctly); the WASIp3 implementation of wasmtime-wasi (default-supported since Wasmtime 46.0.0 - WASIp1 and WASIp2 are not vulnerable because pre-epoch timestamps cannot be represented); and a guest that has been given a preopened filesystem descriptor with MUTABLE access (read-only views are unaffected). Under those conditions the guest simply calls set-times or set-times-at on wasi:filesystem/types.descriptor with a timestamp variant whose signed seconds field is negative (before the epoch). The primary limiting factor is that the host operator must have granted the guest mutable preopened directory access; the main exposure factor is whether guest code is attacker-controlled (e.g., multi-tenant or plugin hosting).

This is a genuine but bounded availability issue, not a widespread emergency. The CVSS 4.0 vector (AV:L/AC:L/AT:N/PR:N/UI:N) with VA:H and VC:N/VI:N correctly frames it as a local, low-complexity denial-of-service with no confidentiality or integrity impact: a sandboxed WebAssembly guest aborts the Unix host process via an assertion failure. The vuln.today decision label is 'this_month' (not act_now/emergency), consistent with a DoS that requires an already-granted capability rather than remote unauthenticated reach. No CISA KEV listing and no EPSS score were provided, and no public exploit or PoC reference is present - only vendor/GHSA and VulnCheck advisories, which are disclosure documents rather than exploit code. The realistic risk is therefore scenario-dependent: high for platforms that run untrusted/multi-tenant WASM guests under WASIp3 on Unix and hand guests a mutable preopened directory, and negligible for deployments on Windows, on WASIp1/WASIp2, with read-only filesystem views, or without WASIp3 enabled. Note the 'local' attack vector here means 'from within the guest sandbox,' which in a serverless/plugin host effectively means any attacker who can submit a module - so the effective exposure depends heavily on whether guest code is attacker-controlled.

An attacker who can run or submit a WebAssembly module to a Wasmtime-based host (e.g., a multi-tenant WASM/serverless platform) on a Unix system running WASIp3, where the guest is given a mutable preopened directory, invokes set-times or set-times-at with a negative pre-epoch seconds value. The guest-supplied timestamp hits a conversion that wrongly asserts the time is after the Unix epoch, triggering an assertion failure that aborts the entire host process and takes down co-located tenants. No public exploit code is identified at time of analysis, and the low attack complexity means a trivial crafted call suffices once the required mutable preopen is present.