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fix: nil pointer dereference DoS via invalid DPoP htu URL #4112

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fix: nil pointer dereference DoS via invalid DPoP htu URL #4112

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64ea568
fix: prevent nil pointer dereference in DPoP strip() for invalid htu …
reinkrul Mar 25, 2026
749dc24
fix: validate htu/htm claim types before type assertion in DPoP Parse()
reinkrul Mar 25, 2026
ee15001
fix: validate htu/htm claim types before type assertion in DPoP Parse()
reinkrul Mar 25, 2026
d3aac13
Apply suggestions from code review
reinkrul Mar 25, 2026
897a262
refactor(dpop): eliminate variable shadowing in Parse() HTU/HTM claim…
Copilot Mar 25, 2026
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29 changes: 20 additions & 9 deletions crypto/dpop/dpop.go
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Original file line number Diff line number Diff line change
Expand Up @@ -158,6 +158,8 @@ func Parse(s string) (*DPoP, error) {
}
if v, ok := token.Get(HTUKey); !ok || v == "" {
return nil, fmt.Errorf("%w: missing htu claim", ErrInvalidDPoP)
} else if _, err := url.Parse(v.(string)); err != nil {
return nil, fmt.Errorf("%w: invalid htu claim: %w", ErrInvalidDPoP, err)
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}
if v, ok := token.Get(HTMKey); !ok || v == "" {
return nil, fmt.Errorf("%w: missing htm claim", ErrInvalidDPoP)
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Expand Down Expand Up @@ -220,22 +222,31 @@ func (t DPoP) Match(jkt string, method string, url string) (bool, error) {
if method != t.HTM() {
return false, fmt.Errorf("method mismatch, token: %s, given: %s", t.HTM(), method)
}
urlLeft := strip(t.HTU())
urlRight := strip(url)
urlLeft, err := strip(t.HTU())
if err != nil {
return false, fmt.Errorf("invalid htu claim: %w", err)
}
urlRight, err := strip(url)
if err != nil {
return false, fmt.Errorf("invalid url: %w", err)
}
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if urlLeft != urlRight {
return false, fmt.Errorf("url mismatch, token: %s, given: %s", urlLeft, urlRight)
}

return true, nil
}

func strip(raw string) string {
url, _ := url.Parse(raw)
url.Scheme = "https"
url.Host = strings.Split(url.Host, ":")[0]
url.RawQuery = ""
url.Fragment = ""
return url.String()
func strip(raw string) (string, error) {
u, err := url.Parse(raw)
if err != nil {
return "", err
}
u.Scheme = "https"
u.Host = strings.Split(u.Host, ":")[0]
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u.RawQuery = ""
u.Fragment = ""
return u.String(), nil
}

func (t DPoP) MarshalJSON() ([]byte, error) {
Expand Down
14 changes: 14 additions & 0 deletions crypto/dpop/dpop_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -229,6 +229,20 @@ func TestParseDPoP(t *testing.T) {
require.Error(t, err)
assert.EqualError(t, err, "invalid DPoP token: jti claim too long")
})
t.Run("invalid htu claim URL", func(t *testing.T) {
// Regression test: url.Parse returns (nil, error) for invalid percent-encoded
// sequences. Without the fix, strip() dereferenced the nil pointer, panicking
// the server when Match() was called on a token with htu="%zz".
dpopToken := New(*request)
_ = dpopToken.Token.Set(HTUKey, "%zz")
dpopString, _ := dpopToken.Sign("kid", keyPair, alg)

_, err := Parse(dpopString)

require.Error(t, err)
assert.ErrorIs(t, err, ErrInvalidDPoP)
assert.Contains(t, err.Error(), "invalid htu claim")
})
}

func TestDPoP_Match(t *testing.T) {
Expand Down
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