Vulnerability · Published Nov 3, 2026 · Assigned by VulnCheck
CVE-2026-121439Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 HTTP Response Splitting via wasi-http
Medium 5.3
In plain English
A medium-severity security flaw in wasmtime from bytecodealliance. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 9% of all known vulnerabilities).
Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.2%top 91.0% of all CVEs
Exploited in the wildNo reportsnot in CISA KEV
Attack toolingNoneno public tooling known
Official description
Wasmtime 46.0.0 before 48.0.7 and 49.0.0 before 49.0.4 contains a response splitting vulnerability in wasi-http p3 that allows guests to set unvalidated content-length headers. Malicious wasip3 guests can splice an existing body into a new response with an incorrect content-length to perform response splitting or injection attacks.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| bytecodealliance | wasmtime | 46.0.0 – before 48.0.749.0.0 – before 49.0.4 |
Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N