Bytecode Alliance Wasmtime wasi-http request smuggling

Summaryinfo

A vulnerability has been found in Bytecode Alliance Wasmtime and classified as problematic. This issue affects some unknown processing of the component wasi-http. Performing a manipulation results in request smuggling. This vulnerability was named CVE-2026-126406. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability was found in Bytecode Alliance Wasmtime (the affected version unknown). It has been classified as problematic. This affects an unknown part of the component wasi-http. The manipulation with an unknown input leads to a request smuggling vulnerability. CWE is classifying the issue as CWE-444. The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. This is going to have an impact on integrity. The summary by CVE is:

The wasmtime-wasi-http p2 implementation in Wasmtime before 36.0.20, 37.0.0 before 48.0.8, 49.0.0 before 49.0.5, and 50.0.0 before 50.0.1 can send conflicting content-length headers, or ones not matching the body, in outgoing requests. A guest that reuses a received response's headers resource to send a bodyless request can enable request smuggling against non-compliant servers, potentially bypassing embedder destination access controls.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-126406 since 11/10/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 11/13/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• Bytecode Alliance

Name

• Wasmtime

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• 🔒

CPE 2.2info

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