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Use constant-time comparison for anti-csrf tokens 

This is probably completely overkill, but since anti-csrf tokens are secrets,
they should be compared against untrusted inputs in constant time.
This commit is contained in:
jvoisin 2024-03-04 00:08:55 +01:00 committed by Frédéric Guillot
parent 9fe99ce7fa
commit d55b410800
2 changed files with 7 additions and 1 deletions
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5
internal/crypto/crypto.go
View File

@ -7,6 +7,7 @@ import (
"crypto/hmac"
"crypto/rand"
"crypto/sha256"
"crypto/subtle"
"encoding/base64"
"encoding/hex"
"fmt"
@ -60,3 +61,7 @@ func GenerateUUID() string {
b := GenerateRandomBytes(16)
return fmt.Sprintf("%X-%X-%X-%X-%X", b[0:4], b[4:6], b[6:8], b[8:10], b[10:])
}
func ConstantTimeCmp(a, b string) bool {
return subtle.ConstantTimeCompare([]byte(a), []byte(b)) == 1
}

3
internal/ui/middleware.go
View File

@ -10,6 +10,7 @@ import (
"net/http"
"miniflux.app/v2/internal/config"
"miniflux.app/v2/internal/crypto"
"miniflux.app/v2/internal/http/cookie"
"miniflux.app/v2/internal/http/request"
"miniflux.app/v2/internal/http/response/html"
@ -92,7 +93,7 @@ func (m *middleware) handleAppSession(next http.Handler) http.Handler {
formValue := r.FormValue("csrf")
headerValue := r.Header.Get("X-Csrf-Token")
if session.Data.CSRF != formValue && session.Data.CSRF != headerValue {
if !crypto.ConstantTimeCmp(session.Data.CSRF, formValue) && !crypto.ConstantTimeCmp(session.Data.CSRF, headerValue) {
slog.Warn("Invalid or missing CSRF token",
slog.Any("url", r.RequestURI),
slog.String("form_csrf", formValue),