Fix cross-vault OCSP snapshot poisoning

ocsp-responder/src/snapshot.rs

@@ -38,6 +38,8 @@ struct RawSnapshot {
 
 #[derive(Debug, Deserialize)]
 struct RawIssuer {
+    #[serde(default)]
+    id: String,
     #[serde(default)]
     sha256: String,
 }
@@ -53,12 +55,22 @@ struct RawEntry {
 }
 
 impl Snapshot {
-    /// Parse and validate a snapshot against the configured CA fingerprint.
-    pub fn parse(bytes: &[u8], expected_sha256: &str) -> Result<Self, SnapshotError> {
+    /// Parse and validate a snapshot against the configured CA identity.
+    pub fn parse(
+        bytes: &[u8],
+        expected_sha256: &str,
+        expected_ca_id: &str,
+    ) -> Result<Self, SnapshotError> {
         let raw: RawSnapshot = serde_json::from_slice(bytes)?;
         if raw.schema != SCHEMA {
             return Err(SnapshotError::Schema(raw.schema));
         }
+        if !raw.issuer.id.eq_ignore_ascii_case(expected_ca_id) {
+            return Err(SnapshotError::IssuerIdMismatch {
+                expected: expected_ca_id.to_string(),
+                actual: raw.issuer.id,
+            });
+        }
         if !raw.issuer.sha256.eq_ignore_ascii_case(expected_sha256) {
             return Err(SnapshotError::IssuerMismatch {
                 expected: expected_sha256.to_string(),
@@ -158,6 +170,8 @@ pub enum SnapshotError {
     Json(#[from] serde_json::Error),
     #[error("unsupported snapshot schema {0:?}")]
     Schema(String),
+    #[error("snapshot issuer ID {actual} does not match configured CA ID {expected}")]
+    IssuerIdMismatch { expected: String, actual: String },
     #[error("snapshot issuer {actual} does not match configured CA {expected}")]
     IssuerMismatch { expected: String, actual: String },
     #[error("invalid serial {0:?}")]
@@ -191,7 +205,7 @@ mod tests {
     #[test]
     fn parses_statuses_and_reasons() {
         let sha = sha256_hex(b"ca");
-        let snapshot = Snapshot::parse(body(&sha).as_bytes(), &sha).unwrap();
+        let snapshot = Snapshot::parse(body(&sha).as_bytes(), &sha, "ca").unwrap();
         let good = snapshot.status_for_serial(&[0x01, 0xab]).unwrap();
         assert_eq!(good.status, Status::Good);
         let revoked = snapshot.status_for_serial(&[0xff]).unwrap();
@@ -203,11 +217,15 @@ mod tests {
     #[test]
     fn rejects_wrong_issuer_schema_and_duplicates() {
         let sha = sha256_hex(b"ca");
-        assert!(Snapshot::parse(body(&sha).as_bytes(), "wrong").is_err());
+        assert!(Snapshot::parse(body(&sha).as_bytes(), "wrong", "ca").is_err());
+        assert!(matches!(
+            Snapshot::parse(body(&sha).as_bytes(), &sha, "other"),
+            Err(SnapshotError::IssuerIdMismatch { .. })
+        ));
         let wrong_schema = body(&sha).replace(SCHEMA, "other");
-        assert!(Snapshot::parse(wrong_schema.as_bytes(), &sha).is_err());
+        assert!(Snapshot::parse(wrong_schema.as_bytes(), &sha, "ca").is_err());
         let duplicate = body(&sha).replace("\"00ff\"", "\"01ab\"");
-        assert!(Snapshot::parse(duplicate.as_bytes(), &sha).is_err());
+        assert!(Snapshot::parse(duplicate.as_bytes(), &sha, "ca").is_err());
     }
 
     #[test]