diff --git a/lib/util/quickder.c b/lib/util/quickder.c
--- a/lib/util/quickder.c
+++ b/lib/util/quickder.c
@@ -757,6 +757,13 @@
                         }
 
                         case SEC_ASN1_BIT_STRING: {
+                            /* Can't be 8 or more spare bits, or any spare bits
+			     * if there are no octets. */
+                            if (temp.data[0] >= 8 || (temp.data[0] > 0 && temp.len == 1)) {
+                                PORT_SetError(SEC_ERROR_BAD_DER);
+                                rv = SECFailure;
+                                break;
+                            }
                             /* change the length in the SECItem to be the number
                                of bits */
                             temp.len = (temp.len - 1) * 8 - (temp.data[0] & 0x7);