Weakness Type (CWE)

CWE-444 — CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

CAPEC

CVSS 4.0 Score

6.3

MEDIUM

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

Vulnerability 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.

Affected

pkg:hex/bandit

Module Source File Routine
Bandit.Headers lib/bandit/headers.ex Bandit.Headers.get_content_length/1
Status Type Version Changes / Fixed in
affected semver ⓘ initial < 1.11.0

pkg:github/mtrudel/bandit

Module Source File Routine
Bandit.Headers lib/bandit/headers.ex Bandit.Headers.get_content_length/1
Status Type Version Changes / Fixed in
affected git ⓘ initial < 1.11.0

References

Credits

  • Finder: Peter Ullrich
  • Remediation developer: Mat Trudel
  • Analyst: Jonatan Männchen

CVE record as JSON:  GET /cves/CVE-2026-39805.json
OSV record as JSON:  GET /osv/EEF-CVE-2026-39805.json