Wasmtime CVE-2026-115391

Exploitation requires the host embedding to use Wasmtime's WASIp3 implementation and to expose file or HTTP write streams to guests, plus the ability to run a malicious/untrusted guest module (reflected as PR:L). The unbounded host buffering is bounded only by the guest's linear memory, so the practical ceiling on memory exhaustion is the guest's linear-memory size. Limiting factors: WASIp3 was not enabled by default in Wasmtime versions prior to 46.0.0, the write-stream path must actually be exercised (AT:P/UI:P), impact is availability-only (no confidentiality or integrity), and hosts that run only trusted guests or do not use WASIp3 streams are not exposed. The GHSA advisory states there is no known workaround and upgrading to 46.0.3 or 47.0.4 is the recommended fix.

This is a denial-of-service issue (CWE-770/400/789, uncontrolled resource allocation) in Wasmtime's WASIp3 file and HTTP write-stream handling, where the host unconditionally copies and buffers a guest-specified-length write, bounded only by the guest's linear memory. The supplied CVSS 4.0 vector (AV:N/AC:L/AT:P/PR:L/UI:P, VC:N/VI:N/VA:H, SC:N/SI:N/SA:H, score 6.9 Medium) is internally consistent with the description: availability-only impact, low privilege (a guest module must already be running), and a passive attack requirement/user interaction. There is no KEV listing, no EPSS score, and no POC in the provided data, so the exploitation signal is: no public exploit identified at time of analysis. The vuln.today decision label is this_month, not act_now or emergency, which matches a Medium-severity availability bug that is serious for multi-tenant/untrusted-guest hosts but is not under active exploitation. The one notable caveat is that PR:L and UI:P encode that the attacker must be able to load/run a guest and that the WASIp3 stream path must be exercised - the CVSS does not describe the trigger mechanism beyond that, and the advisory itself only states the host buffers without limit. Net: a real priority for anyone embedding Wasmtime 46.x/47.x with WASIp3 enabled and running untrusted guests, but lower urgency where guests are trusted or WASIp3 streams are not used.

A multi-tenant or edge host embeds Wasmtime 46.x/47.x with WASIp3 enabled and exposes file or HTTP write streams to untrusted guest modules. A malicious guest offers an extremely large buffer to a write stream, and the host copies and buffers every byte without limit, exhausting host memory and denying service to the host process and co-tenant guests. No public PoC or exploit code is identified in the provided data.