---
id: CVE-2026-105660
title: >-
  Improper Validation of Syntactic Correctness of Input vulnerability in mtrudel
  bandit allows an unauthenticated remote attacker to set conn.host and
  conn.port to values outside the RFC 3986 host grammar via the authority of an
  HTTP/1 abs…
summary: >-
  Improper Validation of Syntactic Correctness of Input vulnerability in mtrudel
  bandit allows an unauthenticated remote attacker to set conn.host and
  conn.port to values outside the RFC 3986 host grammar via the authority of an
  HTTP/1 abs…
severity: medium
cvss: 6.9
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N'
cwe:
  - CWE-1286
vendor: mtrudel
product: bandit
affected:
  - bandit >= 0.6.0 < 1.13.0
  - >-
    mtrudel/bandit >= 0e3edda0edf6322e9164b827c6d3ddecd080ff2e <
    6ea80210137b3f69caf65f67398934259dc365d0
published: '2026-10-15'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T19:17:16.290'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-105660'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-105660.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/mtrudel/bandit/commit/0e3edda0edf6322e9164b827c6d3ddecd080ff2e
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/mtrudel/bandit/commit/6ea80210137b3f69caf65f67398934259dc365d0
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://github.com/mtrudel/bandit/security/advisories/GHSA-v53v-9hvg-37jf'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-105660'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
  - cve.org
cvssSource: cna
ingestedAt: '2026-10-15T19:25:46.396Z'
---

## Overview

Improper Validation of Syntactic Correctness of Input vulnerability in mtrudel bandit allows an unauthenticated remote attacker to set conn.host and conn.port to values outside the RFC 3986 host grammar via the authority of an HTTP/1 absolute-form or authority-form request target. Bandit validates the Host header and answers 400 when it is malformed, but when the request target carries its own authority that authority takes precedence, as RFC 9112 requires, and Bandit.Pipeline.determine_host_and_port!/4 in lib/bandit/pipeline.ex passes it to the application unchecked. A request line such as GET http://good.example@evil.example/x HTTP/1.1 with a valid Host header yields a conn.host of good.example@evil.example, and the same path admits NUL, DEL and non-ASCII bytes, invalid IP literals and ports outside 1..65535. The HTTP/1.0 clause needs no Host header at all, and CONNECT places the unparsed port string in conn.port.

Applications that build absolute URLs from conn.host, such as through Plug.Conn.request_url/1 or Phoenix URL helpers, emit links whose authority the attacker chose. Message framing is unaffected, and no CR or LF can reach conn.host.

This issue affects bandit: from 0.6.0 before 1.13.0.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.