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fix(serve/auth): handle crypto/rand.Read error in signSession #5285

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SivanCola merged 2 commits into from
Jun 25, 2026
+8 −1
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fix(serve/auth): handle crypto/rand.Read error in signSession #5285

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2495efc
fix(serve/auth): handle crypto/rand.Read error in signSession
YoungDan-hero Jun 25, 2026
d4aadbb
docs(serve/auth): correct signSession nonce-panic comment
SivanCola Jun 25, 2026
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9 changes: 8 additions & 1 deletion internal/serve/auth.go
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Original file line number Diff line number Diff line change
Expand Up @@ -456,7 +456,14 @@ func redirectToSafeTarget(w http.ResponseWriter, r *http.Request, raw string, st
func (ag *authGate) signSession() string {
expiry := time.Now().Add(sessionDuration).Unix()
nonce := make([]byte, 16)
_, _ = rand.Read(nonce)
if _, err := rand.Read(nonce); err != nil {
// crypto/rand.Read cannot fail on modern systems; panic rather than
// fall back to an all-zero nonce. Forging a cookie still requires the
// PBKDF2-derived sessKey, so this is not an auth bypass, but a constant
// nonce weakens session token uniqueness/unpredictability and is the
// same anti-pattern generateToken/sessionKeyForPasswordHash panic on.
panic("serve/auth: crypto/rand.Read failed: " + err.Error())
}

payload := strconv.FormatInt(expiry, 10) + "|" + base64.RawURLEncoding.EncodeToString(nonce)
mac := hmac.New(sha256.New, ag.sessKey)
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