CVE-2026-39805 – CL.CL HTTP request smuggling via duplicate Content-Length in bandit

CVE ID :CVE-2026-39805

Published : May 1, 2026, 9:16 p.m. | 1 hour, 3 minutes ago

Description :Inconsistent Interpretation of HTTP Requests vulnerability in mtrudel bandit allows HTTP request smuggling via duplicate Content-Length headers.

‚Elixir.Bandit.Headers‘:get_content_length/1 in lib/bandit/headers.ex uses List.keyfind/3, which returns only the first matching header. When a request contains two Content-Length headers with different values, Bandit silently accepts it, uses the first value to read the body, and dispatches the remaining bytes as a second pipelined request on the same keep-alive connection. RFC 9112 §6.3 requires recipients to treat this as an unrecoverable framing error.

When Bandit sits behind a proxy that picks the last Content-Length value and forwards the request rather than rejecting it, an unauthenticated attacker can smuggle requests past edge WAF rules, path-based ACLs, rate limiting, and audit logging.

This issue affects bandit: before 1.11.0.

Severity: 6.3 | MEDIUM

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