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fix(oauth): compare redirect URI paths in encoded form, reject any '#' #296

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fix(oauth): compare redirect URI paths in encoded form, reject any '#' #296

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16 changes: 9 additions & 7 deletions internal/oauth/redirect.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,15 +19,17 @@ import (
// redirectURIAllowed reports whether uri is permitted for use as an OAuth
// redirect target, given the configured allowed list. Matching is exact
// (scheme and host compared case-insensitively; everything else,
// including the path, byte-for-byte), except that a loopback host
// (127.0.0.1, [::1] or localhost) may use any port so long as its scheme,
// host and path match an allowed entry with the same host. A URI carrying
// including the path in its percent-encoded form, byte-for-byte), except
// that a loopback host (127.0.0.1, [::1] or localhost) may use any port
// so long as its scheme, host and path match an allowed entry with the
// same host. A URI carrying
// userinfo (e.g. "http://attacker@127.0.0.1/callback") is always rejected,
// since a browser silently drops it and it exists only to mislead a
// reviewer of the URI.
// reviewer of the URI. So is one containing "#", even with an empty
// fragment, since RFC 6749 section 3.1.2 forbids fragments outright.
func redirectURIAllowed(uri string, allowed []string) bool {
u, err := url.Parse(uri)
if err != nil || u.Scheme == "" || u.Host == "" || u.Fragment != "" || u.User != nil {
if err != nil || u.Scheme == "" || u.Host == "" || u.User != nil || strings.Contains(uri, "#") {
return false
}

Expand All @@ -37,11 +39,11 @@ func redirectURIAllowed(uri string, allowed []string) bool {
continue
}
if strings.EqualFold(u.Scheme, au.Scheme) && strings.EqualFold(u.Host, au.Host) &&
u.Path == au.Path && u.RawQuery == au.RawQuery {
u.EscapedPath() == au.EscapedPath() && u.RawQuery == au.RawQuery {
return true
}
if isLoopbackHostname(u.Hostname()) && strings.EqualFold(u.Hostname(), au.Hostname()) &&
strings.EqualFold(u.Scheme, au.Scheme) && u.Path == au.Path && u.RawQuery == "" && au.RawQuery == "" {
strings.EqualFold(u.Scheme, au.Scheme) && u.EscapedPath() == au.EscapedPath() && u.RawQuery == "" && au.RawQuery == "" {
return true
}
}
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5 changes: 5 additions & 0 deletions internal/oauth/redirect_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,11 @@ func TestRedirectURIAllowed(t *testing.T) {
"http://attacker@127.0.0.1:9999/callback": false,
"HTTPS://Claude.AI/api/mcp/auth_callback": true,
"https://claude.ai/API/mcp/auth_callback": false,
"http://localhost:@192.0.2.1:5555/callback": false,
"https://claude.ai/api%2Fmcp/auth_callback": false,
"http://127.0.0.1:53211/call%62ack": false,
"https://claude.ai/api/mcp/auth_callback#": false,
"http://localhost:8000/callback#frag": false,
}
for uri, want := range cases {
if got := redirectURIAllowed(uri, allowed); got != want {
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