CVE-2026-34987
Winch backend flaw: guest WASM can access host memory, risking DoS or RCE.
Is CVE-2026-34987 being exploited?
Not confirmed. CVE-2026-34987 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.28% probability of exploitation in the next 30 days.
How severe is CVE-2026-34987?
CVE-2026-34987 is rated Critical with a CVSS score of 9.0. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-34987?
Yes. A fix has been recorded for CVE-2026-34987. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-34987 affect?
CVE-2026-34987 affects Wasmtime with Winch backend (versions with -Ccompiler=winch). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-34987?
Upgrade Wasmtime to non-vulnerable builds (>=36.0.7, 42.0.2, or 43.0.1)
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Host memory access beyond sandbox; DoS, data leakage, or arbitrary RCE via Winch.
Patch when possible
- affected>= 25.0.0 and < 36.0.7
- affected>= 37.0.0 and < 42.0.2
- affected>= 43.0.0 and < 44.0.1
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.