CVE-2026-39805
MediumCVSS 6.3Exploitation Probability (EPSS)
Low risk41th percentile - higher than 41% of all known CVEs
Summary
A vulnerability in the Bandit library (Elixir) allows HTTP request smuggling via duplicate Content-Length headers. The server accepts the first header and treats the remaining data as a subsequent request on the same connection.
Risk Assessment
An attacker can bypass WAF rules, ACLs, rate limiting, and audit logging by smuggling requests through a proxy.
Recommendation
Update the Bandit library to version 1.11.0 or later.
Original NVD description (English source)
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.