{"id":"EEF-CVE-2026-39807","summary":"Client-supplied URI scheme trusted without transport verification in bandit","details":"## Summary\n\nReliance on Untrusted Inputs in a Security Decision vulnerability in mtrudel bandit allows unauthenticated transport-state spoofing on plaintext HTTP connections.\n\n'Elixir.Bandit.Pipeline':determine_scheme/2 in lib/bandit/pipeline.ex returns the client-supplied URI scheme verbatim, ignoring the transport's secure? flag. HTTP/1.1 absolute-form request targets (e.g. GET https://victim/path HTTP/1.1) and the HTTP/2 :scheme pseudo-header are both attacker-controlled strings that flow through this function. Over a plaintext TCP connection, a client can declare https and Bandit will set conn.scheme = :https even though no TLS was negotiated.\n\nDownstream Plug consumers that branch on conn.scheme are silently misled: Plug.SSL's already-secure branch skips its HTTP→HTTPS redirect, cookies emitted with secure: true are sent over plaintext, audit logs record requests as having arrived over HTTPS, and CSRF/SameSite gating may make incorrect decisions.\n\nThis issue affects bandit: from 1.0.0 before 1.11.0.\n\n## Configuration\n\nThe vulnerable system must be accepting plaintext (non-TLS) HTTP connections, either directly or via h2c. Deployments that exclusively use TLS are not affected.","aliases":["CVE-2026-39807","GHSA-375f-4r2h-f99j"],"modified":"2026-05-04T17:30:06.403992Z","published":"2026-05-01T20:34:22.832Z","database_specific":{"cpe_ids":["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"],"capec_ids":["CAPEC-220"],"cwe_ids":["CWE-807"]},"references":[{"type":"ADVISORY","url":"https://github.com/mtrudel/bandit/security/advisories/GHSA-375f-4r2h-f99j"},{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-39807.html"},{"type":"FIX","url":"https://github.com/mtrudel/bandit/commit/45feea20dea8af7ffd7245271107b695c040e667"},{"type":"PACKAGE","url":"https://hex.pm/packages/bandit"}],"affected":[{"package":{"name":"bandit","ecosystem":"Hex","purl":"pkg:hex/bandit"},"ranges":[{"type":"SEMVER","events":[{"introduced":"1.0.0"},{"fixed":"1.11.0"}]}],"versions":["1.0.0","1.1.0","1.1.1","1.1.2","1.1.3","1.2.0","1.2.1","1.2.2","1.2.3","1.3.0","1.4.0","1.4.1","1.4.2","1.5.0","1.5.1","1.5.2","1.5.3","1.5.4","1.5.5","1.5.6","1.5.7","1.6.0","1.6.1","1.6.2","1.6.3","1.6.4","1.6.5","1.6.6","1.6.7","1.6.8","1.6.9","1.6.10","1.6.11","1.7.0","1.8.0","1.9.0","1.10.0","1.10.1","1.10.2","1.10.3","1.10.4"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-39807.json"}},{"ranges":[{"type":"GIT","repo":"https://github.com/mtrudel/bandit","events":[{"introduced":"ff2f829326cd5dcf7335939aef9775269d881e28"},{"fixed":"45feea20dea8af7ffd7245271107b695c040e667"}]}],"versions":["1.0.0","1.0.0-pre.10","1.0.0-pre.11","1.0.0-pre.12","1.0.0-pre.13","1.0.0-pre.14","1.0.0-pre.15","1.0.0-pre.16","1.0.0-pre.17","1.0.0-pre.18","1.0.0-pre.6","1.0.0-pre.7","1.0.0-pre.8","1.0.0-pre.9","1.1.0","1.1.1","1.1.2","1.1.3","1.10.0","1.10.1","1.10.2","1.10.3","1.10.4","1.2.0","1.2.3","1.3.0","1.4.0","1.4.1","1.4.2","1.5.0","1.5.1","1.5.2","1.5.3","1.5.4","1.5.5","1.5.6","1.5.7","1.6.0","1.6.1","1.6.10","1.6.11","1.6.2","1.6.3","1.6.4","1.6.5","1.6.6","1.6.7","1.6.8","1.6.9","1.7.0","1.8.0","1.9.0"],"database_specific":{"source":"https://cna.erlef.org/osv/EEF-CVE-2026-39807.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"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"}],"credits":[{"name":"Peter Ullrich","type":"FINDER"},{"name":"Mat Trudel","type":"REMEDIATION_DEVELOPER"},{"name":"Jonatan Männchen","type":"ANALYST"}]}