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Backport(v1.19) output: enforce strict path boundary validation for tag #5391

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Merged
kenhys merged 1 commit into from
Jun 25, 2026
+145 −1
Merged

Backport(v1.19) output: enforce strict path boundary validation for tag #5391

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23 changes: 22 additions & 1 deletion lib/fluent/plugin/output.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,8 @@ class Output < Base
CHUNK_KEY_PLACEHOLDER_PATTERN = /\$\{([-_.@$a-zA-Z0-9]+)\}/
CHUNK_TAG_PLACEHOLDER_PATTERN = /\$\{(tag(?:\[-?\d+\])?)\}/
CHUNK_ID_PLACEHOLDER_PATTERN = /\$\{chunk_id\}/
INVALID_PATH_COMPONENT_PATTERN = %r{\.\.[/\\]|^[/\\]}
PARENT_DIRECTORY_PATTERN = %r{\.\.[/\\]}

CHUNKING_FIELD_WARN_NUM = 4

Expand Down Expand Up @@ -825,9 +827,17 @@ def extract_placeholders(str, chunk)
# ${tag}, ${tag[0]}, ${tag[1]}, ... , ${tag[-2]}, ${tag[-1]}
if @chunk_key_tag
if str.include?('${tag}')
if metadata.tag.match?(INVALID_PATH_COMPONENT_PATTERN)
raise Fluent::UnrecoverableError, "Invalid path component detected in tag: #{metadata.tag}"
end

rvalue = rvalue.gsub('${tag}', metadata.tag)
end
if CHUNK_TAG_PLACEHOLDER_PATTERN.match?(str)
if metadata.tag.match?(INVALID_PATH_COMPONENT_PATTERN)
raise Fluent::UnrecoverableError, "Invalid path component detected in tag: #{metadata.tag}"
end

hash = {}
tag_parts = metadata.tag.split('.')
tag_parts.each_with_index do |part, i|
Expand Down Expand Up @@ -858,10 +868,21 @@ def extract_placeholders(str, chunk)
end

rvalue = rvalue.gsub(CHUNK_KEY_PLACEHOLDER_PATTERN) do |matched|
hash.fetch(matched) do
replace = hash.fetch(matched) do
log.warn "chunk key placeholder '#{matched[2..-2]}' not replaced. template:#{str}"
''
end
if replace.to_s.match?(INVALID_PATH_COMPONENT_PATTERN)
raise Fluent::UnrecoverableError, "Invalid path component detected in #{matched}: #{replace}"
end

replace
end
# Check if the number of parent directory components (../) has increased due to variable substitution
if rvalue.match?(PARENT_DIRECTORY_PATTERN)
if rvalue.scan(PARENT_DIRECTORY_PATTERN).size > str.scan(PARENT_DIRECTORY_PATTERN).size
raise Fluent::UnrecoverableError, "Invalid path component detected, replaced to: #{rvalue}"
end
end
end

Expand Down
123 changes: 123 additions & 0 deletions test/plugin/test_output.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -448,6 +448,129 @@ def waiting(seconds)
assert { logs.any? { |log| log.include?("chunk key placeholder 'key2' not replaced. template:#{tmpl}") } }
end

sub_test_case 'Path boundary validation for ${tag} placeholder' do
data(
'normal_dot' => 'app.web',
'safe_slash' => 'app/web',
'symbol_mixed' => 'my_tag-123',
'no_match' => 'app..web/log',
)
test 'allows valid tags including safe slashes' do |tag|
@i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'tag')]))
t = event_time('2016-04-11 20:30:00 +0900')
v = { key1: "value1" }
m = create_metadata(timekey: t, tag: tag, variables: v)
result = @i.extract_placeholders("/data/${tag}/log", m)
assert_equal "/data/#{tag}/log", result
end

data(
'unix_relative' => '../etc/cron.d',
'windows_relative' => '..\\Windows\\System32',
'unix_absolute' => '/etc/passwd',
'windows_absolute' => '\\Windows'
)
test 'rejects tags containing parent directory relative or absolute root paths' do |tag|
@i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'tag')]))
t = event_time('2016-04-11 20:30:00 +0900')
v = { key1: "value1" }
m = create_metadata(timekey: t, tag: tag, variables: v)

err = assert_raise(Fluent::UnrecoverableError) do
@i.extract_placeholders("/data/${tag}/log", m)
end
assert_match(/Invalid path component detected in tag/, err.message)
end

data(
'unix_relative' => '../etc/cron.d',
'windows_relative' => '..\\Windows\\System32',
'unix_absolute' => '/etc/passwd',
'windows_absolute' => '\\Windows'
)
test 'rejects tags containing traversal paths even when only parts are used' do |tag|
@i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'tag')]))
t = event_time('2016-04-11 20:30:00 +0900')
v = { key1: "value1" }
m = create_metadata(timekey: t, tag: tag, variables: v)

err = assert_raise(Fluent::UnrecoverableError) do
@i.extract_placeholders("/data/${tag[0]}/log", m)
end
assert_match(/Invalid path component detected in tag/, err.message)
end

data(
'unix_relative' => '../etc/cron.d',
'windows_relative' => '..\\Windows\\System32',
'unix_absolute' => '/etc/passwd',
'windows_absolute' => '\\Windows'
)
test 'rejects variables containing parent directory relative or absolute root paths' do |var_value|
@i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'tag,file')]))
t = event_time('2016-04-11 20:30:00 +0900')
v = { file: var_value }
m = create_metadata(timekey: t, tag: 'app.web', variables: v)

err = assert_raise(Fluent::UnrecoverableError) do
@i.extract_placeholders("/data/${tag}/${file}", m)
end
assert_match(/Invalid path component detected in \$\{file\}/, err.message)
end

data(
'combined ../' => { dot: '.', dotslash: './', file: 'safe.log' },
'combined ..\\' => { dot: '.', dotslash: '.\\', file: 'safe.log' },
)
test 'rejects combined variables containing dot and slash combination' do |var_value|
@i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'tag,dot,dotslash,file')]))
t = event_time('2016-04-11 20:30:00 +0900')
v = var_value
m = create_metadata(timekey: t, tag: 'app.web', variables: v)

err = assert_raise(Fluent::UnrecoverableError) do
@i.extract_placeholders("/data/${dot}${dotslash}${file}", m)
end
assert_match(/Invalid path component detected, replaced to/, err.message)
end

test 'passes safely when placeholder expansion does NOT introduce additional ../' do
@i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'val1,val2,val3')]))
t = event_time('2016-04-11 20:30:00 +0900')
v = { val1: "safe", val2: "." }
m = create_metadata(timekey: t, variables: v)

result = @i.extract_placeholders("../data/${val1}${val2}log", m)
assert_equal "../data/safe.log", result
end

data(
'normal_string' => 'app.log',
'safe_slash' => 'logs/app.log',
'integer_val' => 80,
'boolean_val' => true
)
test 'allows valid variables including safe strings and non-string types' do |var_value|
@i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'tag,file')]))
t = event_time('2016-04-11 20:30:00 +0900')
v = { file: var_value }
m = create_metadata(timekey: t, tag: 'app.web', variables: v)

result = @i.extract_placeholders("/data/${tag}/${file}", m)
assert_equal "/data/app.web/#{var_value}", result
end

test 'skips validation if ${tag} placeholder is not used' do
@i.configure(config_element('ROOT', '', {}, [config_element('buffer', 'tag')]))
t = event_time('2016-04-11 20:30:00 +0900')
v = { key1: "value1" }
m = create_metadata(timekey: t, tag: '../etc/passwd', variables: v)

result = @i.extract_placeholders("/data/static/log", m)
assert_equal "/data/static/log", result
end
end

sub_test_case '#placeholder_validators' do
test 'returns validators for time, tag and keys when a template has placeholders even if plugin is not configured with these keys' do
@i.configure(config_element('ROOT', '', {}, [config_element('buffer', '')]))
Expand Down
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