Bug 2565921 (CVE-2026-121439)

Summary: CVE-2026-121439 wasmtime: wasmtime: Response splitting via unvalidated Content-Length headers in wasi-http
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in wasmtime. The wasi-http component fails to properly validate Content-Length headers when processing network responses. A malicious WebAssembly guest can supply an invalid Content-Length header and splice response bodies, allowing HTTP (Hypertext Transfer Protocol) response splitting and injection attacks against downstream clients or proxies.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-11-03 16:19:19 UTC
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.