commit 0a997082fe5e96d11c0a38c309299445f50c1fe8
author Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Thu Apr 09 12:31:52 2020 +0200
committer Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Thu Apr 09 12:31:52 2020 +0200
tree a299891e3b14b9d8577933c2c9b50af1583a68b6
parent f1bd55fd163a11b1fa65f358105c33117c4115eb
parent 6e0806b338aa3475b4d538a146d53cc348024258

Merge branch 'mbedtls-2.7-restricted' into prepare-rc-2.7.15-update

* mbedtls-2.7-restricted:
  Parse HelloVerifyRequest buffer overread: add changelog entry
  Parse HelloVerifyRequest: avoid buffer overread at the start
  Parse HelloVerifyRequest: avoid buffer overread on the cookie

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index fa0448d..f6b4cef 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -15,6 +15,8 @@
      untrusted operating system attacking a secure enclave) to fully recover
      an ECDSA private key. Found and reported by Alejandro Cabrera Aldaya,
      Billy Brumley and Cesar Pereida Garcia. CVE-2020-10932
+   * Fix a potentially remotely exploitable buffer overread in a
+     DTLS client when parsing the Hello Verify Request message.
 
 Bugfix
    * Fix compilation failure when both MBEDTLS_SSL_PROTO_DTLS and

library/ssl_cli.c

diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index 0d3623e..07cc5dd 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -1411,6 +1411,19 @@
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse hello verify request" ) );
 
+    /* Check that there is enough room for:
+     * - 2 bytes of version
+     * - 1 byte of cookie_len
+     */
+    if( mbedtls_ssl_hs_hdr_len( ssl ) + 3 > ssl->in_msglen )
+    {
+        MBEDTLS_SSL_DEBUG_MSG( 1,
+            ( "incoming HelloVerifyRequest message is too short" ) );
+        mbedtls_ssl_send_alert_message( ssl, MBEDTLS_SSL_ALERT_LEVEL_FATAL,
+                                    MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
+        return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
+    }
+
     /*
      * struct {
      *   ProtocolVersion server_version;
@@ -1439,8 +1452,6 @@
     }
 
     cookie_len = *p++;
-    MBEDTLS_SSL_DEBUG_BUF( 3, "cookie", p, cookie_len );
-
     if( ( ssl->in_msg + ssl->in_msglen ) - p < cookie_len )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1,
@@ -1449,6 +1460,7 @@
                                     MBEDTLS_SSL_ALERT_MSG_DECODE_ERROR );
         return( MBEDTLS_ERR_SSL_BAD_HS_SERVER_HELLO );
     }
+    MBEDTLS_SSL_DEBUG_BUF( 3, "cookie", p, cookie_len );
 
     mbedtls_free( ssl->handshake->verify_cookie );