{"containers":{"cna":{"affected":[{"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"],"defaultStatus":"unaffected","modules":["'Elixir.Bandit.Pipeline'"],"packageName":"bandit","packageURL":"pkg:hex/bandit","product":"bandit","programFiles":["lib/bandit/pipeline.ex"],"programRoutines":[{"name":"'Elixir.Bandit.Pipeline':determine_scheme/2"}],"repo":"https://github.com/mtrudel/bandit","vendor":"mtrudel","versions":[{"lessThan":"1.11.0","status":"affected","version":"1.0.0","versionType":"semver"}]},{"collectionURL":"https://github.com","cpes":["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"],"defaultStatus":"unaffected","modules":["'Elixir.Bandit.Pipeline'"],"packageName":"mtrudel/bandit","packageURL":"pkg:github/mtrudel/bandit","product":"bandit","programFiles":["lib/bandit/pipeline.ex"],"programRoutines":[{"name":"'Elixir.Bandit.Pipeline':determine_scheme/2"}],"repo":"https://github.com/mtrudel/bandit","vendor":"mtrudel","versions":[{"lessThan":"1.11.0","status":"affected","version":"ff2f829326cd5dcf7335939aef9775269d881e28","versionType":"git"}]}],"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"<p>The vulnerable system must be accepting plaintext (non-TLS) HTTP connections, either directly or via h2c. Deployments that exclusively use TLS are not affected.</p>"}],"value":"The vulnerable system must be accepting plaintext (non-TLS) HTTP connections, either directly or via h2c. Deployments that exclusively use TLS are not affected."}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*","versionEndExcluding":"1.11.0","versionStartIncluding":"1.0.0","vulnerable":true}],"negate":false,"operator":"OR"}],"operator":"AND"}],"credits":[{"lang":"en","type":"finder","value":"Peter Ullrich"},{"lang":"en","type":"remediation developer","value":"Mat Trudel"},{"lang":"en","type":"analyst","value":"Jonatan Männchen"}],"descriptions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"Reliance on Untrusted Inputs in a Security Decision vulnerability in mtrudel bandit allows unauthenticated transport-state spoofing on plaintext HTTP connections.<p><tt>'Elixir.Bandit.Pipeline':determine_scheme/2</tt> in <tt>lib/bandit/pipeline.ex</tt> returns the client-supplied URI scheme verbatim, ignoring the transport's <tt>secure?</tt> flag. HTTP/1.1 absolute-form request targets (e.g. <tt>GET https://victim/path HTTP/1.1</tt>) and the HTTP/2 <tt>:scheme</tt> pseudo-header are both attacker-controlled strings that flow through this function. Over a plaintext TCP connection, a client can declare <tt>https</tt> and Bandit will set <tt>conn.scheme = :https</tt> even though no TLS was negotiated.</p><p>Downstream Plug consumers that branch on <tt>conn.scheme</tt> are silently misled: <tt>Plug.SSL</tt>'s already-secure branch skips its HTTP→HTTPS redirect, cookies emitted with <tt>secure: true</tt> are sent over plaintext, audit logs record requests as having arrived over HTTPS, and CSRF/SameSite gating may make incorrect decisions.</p><p>This issue affects bandit: from 1.0.0 before 1.11.0.</p>"}],"value":"Reliance 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."}],"impacts":[{"capecId":"CAPEC-220","descriptions":[{"lang":"en","value":"CAPEC-220 Client-Server Protocol Manipulation"}]}],"metrics":[{"cvssV4_0":{"attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":6.3,"baseSeverity":"MEDIUM","privilegesRequired":"NONE","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"LOW","vulnIntegrityImpact":"LOW"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-807","description":"CWE-807 Reliance on Untrusted Inputs in a Security Decision","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-05-01T20:34:22.832Z","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","shortName":"EEF"},"references":[{"tags":["vendor-advisory","related"],"url":"https://github.com/mtrudel/bandit/security/advisories/GHSA-375f-4r2h-f99j"},{"tags":["related"],"url":"https://cna.erlef.org/cves/CVE-2026-39807.html"},{"tags":["related"],"url":"https://osv.dev/vulnerability/EEF-CVE-2026-39807"},{"tags":["patch"],"url":"https://github.com/mtrudel/bandit/commit/45feea20dea8af7ffd7245271107b695c040e667"}],"source":{"discovery":"EXTERNAL"},"title":"Client-supplied URI scheme trusted without transport verification in bandit","x_generator":{"engine":"cvelib 1.8.0"}}},"cveMetadata":{"assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","assignerShortName":"EEF","cveId":"CVE-2026-39807","datePublished":"2026-05-01T20:34:22.832Z","dateReserved":"2026-04-07T12:28:54.916Z","dateUpdated":"2026-05-01T20:34:22.832Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"}