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fix lack of escaping of filename in Content-Disposition #3556

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merged 3 commits into from
May 29, 2023
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fix lack of escaping of filename in Content-Disposition #3556

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ded02a8
fix lack of escaping of filename in Content-Disposition
motoyasu-saburi Apr 1, 2023
96c3c55
add test for Content-Disposition filename escaping process
motoyasu-saburi Apr 1, 2023
ee5b2c9
fix filename escape bypass problem
motoyasu-saburi May 13, 2023
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2 changes: 1 addition & 1 deletion context.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1056,7 +1056,7 @@ func (c *Context) FileFromFS(filepath string, fs http.FileSystem) {
// On the client side, the file will typically be downloaded with the given filename
func (c *Context) FileAttachment(filepath, filename string) {
if isASCII(filename) {
c.Writer.Header().Set("Content-Disposition", `attachment; filename="`+filename+`"`)
c.Writer.Header().Set("Content-Disposition", `attachment; filename="`+strings.Replace(filename, "\"", "\\\"", -1)+`"`)
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This can fix this specific situation (that enables RFD attack) but what about using filePath#Clean?

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I tried using that method,
but the " was not escaped (or URL Encoded), so The vulnerability was not fixed.

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But since it's for file reading those quotes will be needed? File params would be readable with or without it, isn't?

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@fabricioereche

Perhaps you are confusing the file name with the file path.
There may be some misunderstandings, so I will add to this.

The first thing to escape is the filename. Not filepath.

The second thing, The Filename escape requirements are then as follows

  • " --> %2F, \"
  • \r --> %0D, \\r
  • \n --> %0A, \\n

The third thing,
This line is the process of "escaping the 'file name at download time' on the HTTP Response Header.
In other words, filepath is irrelevant.

(The part that actually reads the file is the following line (filepath) )
https://github.com/gin-gonic/gin/pull/3556/files#diff-552f47512a00afe5fc6850cc9ddc830a6daeca162750e50aab4ed549685e0253R1063

But since it's for file reading those quotes will be needed? File params would be readable with or without it, isn't?

This is answered by the third matter mentioned above.
This tells the Request side to "download the file with this kind of file name".
It is not the file path to be read by the Server side.

Does this answer your question?

} else {
c.Writer.Header().Set("Content-Disposition", `attachment; filename*=UTF-8''`+url.QueryEscape(filename))
}
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14 changes: 14 additions & 0 deletions context_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1032,6 +1032,20 @@ func TestContextRenderAttachment(t *testing.T) {
assert.Equal(t, fmt.Sprintf("attachment; filename=\"%s\"", newFilename), w.Header().Get("Content-Disposition"))
}

func TestContextRenderAndEscapeAttachment(t *testing.T) {
w := httptest.NewRecorder()
c, _ := CreateTestContext(w)
maliciousFilename := "tampering_field.sh\";dummy=.go"
actualEscapedResponseFilename := "tampering_field.sh\\\";dummy=.go"

c.Request, _ = http.NewRequest("GET", "/", nil)
c.FileAttachment("./gin.go", maliciousFilename)

assert.Equal(t, 200, w.Code)
assert.Contains(t, w.Body.String(), "func New() *Engine {")
assert.Equal(t, fmt.Sprintf("attachment; filename=\"%s\"", actualEscapedResponseFilename), w.Header().Get("Content-Disposition"))
}

func TestContextRenderUTF8Attachment(t *testing.T) {
w := httptest.NewRecorder()
c, _ := CreateTestContext(w)
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