Vulnerability · Published Nov 3, 2026 · Assigned by VulnCheck

CVE-2026-121441Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 wasi-http Request Smuggling

Low 3.7

In plain English

A low-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 13% of all known vulnerabilities).

Severity (CVSS 3.1)3.7Low

Exploit odds (30 days)0.2%top 86.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 contains a request smuggling vulnerability in wasi-http that allows guests to set multiple conflicting content-length headers. Malicious guests can make the host send HTTP requests with conflicting content-length values to smuggle requests through servers or intermediaries that do not reject them.

Affected products (as reported)

Vendor	Product	Versions
bytecodealliance	wasmtime	0 – before 36.0.1937.0.0 – before 48.0.749.0.0 – before 49.0.4

Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

References

GitHub Security Advisory (GHSA-r8xh-cgf7-392j) vendor-advisory
VulnCheck Advisory: Wasmtime before 36.0.19, 37.0.0 before 48.0.7, and 49.0.0 before 49.0.4 wasi-http Request Smuggling third-party-advisory