Commit aef4b0a5 authored by Kerri Miller's avatar Kerri Miller

Reject slug+uri concat if slug is deemed unsafe

First reported:
  https://gitlab.com/gitlab-org/gitlab-ce/issues/60143

When the page slug is "javascript:" and we attempt to link to a relative
path (using `.` or `..`) the code will concatenate the slug and the uri.
This MR adds a guard to that concat step that will return `nil` if the
incoming slug matches against any of the "unsafe" slug regexes;
currently this is only for the slug "javascript:" but can be extended if
needed. Manually tested against a non-exhaustive list from OWASP of
common javascript XSS exploits that have to to with mangling the
"javascript:" method, and all are caught by this change or by existing
code that ingests the user-specified slug.
parent cf8df783
---
title: Filter relative links in wiki for XSS
merge_request:
author:
type: security
......@@ -4,6 +4,8 @@ module Banzai
module Filter
class WikiLinkFilter < HTML::Pipeline::Filter
class Rewriter
UNSAFE_SLUG_REGEXES = [/\Ajavascript:/i].freeze
def initialize(link_string, wiki:, slug:)
@uri = Addressable::URI.parse(link_string)
@wiki_base_path = wiki && wiki.wiki_base_path
......@@ -35,6 +37,8 @@ module Banzai
# Of the form `./link`, `../link`, or similar
def apply_hierarchical_link_rules!
return if slug_considered_unsafe?
@uri = Addressable::URI.join(@slug, @uri) if @uri.to_s[0] == '.'
end
......@@ -54,6 +58,10 @@ module Banzai
def repository_upload?
@uri.relative? && @uri.path.starts_with?(Wikis::CreateAttachmentService::ATTACHMENT_PATH)
end
def slug_considered_unsafe?
UNSAFE_SLUG_REGEXES.any? { |r| r.match?(@slug) }
end
end
end
end
......
......@@ -70,5 +70,47 @@ describe Banzai::Filter::WikiLinkFilter do
expect(filtered_link.attribute('href').value).to eq(invalid_link)
end
end
context "when the slug is deemed unsafe or invalid" do
let(:link) { "alert(1);" }
invalid_slugs = [
"javascript:",
"JaVaScRiPt:",
"\u0001java\u0003script:",
"javascript :",
"javascript: ",
"javascript : ",
":javascript:",
"javascript&#58;",
"javascript&#0058;",
"javascript&#x3A;",
"javascript&#x003A;",
"java\0script:",
" &#14; javascript:"
]
invalid_slugs.each do |slug|
context "with the slug #{slug}" do
it "doesn't rewrite a (.) relative link" do
filtered_link = filter(
"<a href='.#{link}'>Link</a>",
project_wiki: wiki,
page_slug: slug).children[0]
expect(filtered_link.attribute('href').value).not_to include(slug)
end
it "doesn't rewrite a (..) relative link" do
filtered_link = filter(
"<a href='..#{link}'>Link</a>",
project_wiki: wiki,
page_slug: slug).children[0]
expect(filtered_link.attribute('href').value).not_to include(slug)
end
end
end
end
end
end
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