patch to cracklib 2.7 based on a patch for cracklib 2.9 from
https://bugzilla.redhat.com/attachment.cgi?id=1188599 :

It is not safe to pass words longer than STRINGSIZE further to cracklib
so the longbuffer cannot be longer than STRINGSIZE.

--- ./cracklib/fascist.c.orig	1997-12-31 10:26:46.000000000 +0000
+++ ./cracklib/fascist.c	2016-10-27 19:00:46.000000000 +0000
@@ -490,7 +490,7 @@ FascistGecos(password, uid)
     char gbuffer[STRINGSIZE];
     char tbuffer[STRINGSIZE];
     char *uwords[STRINGSIZE];
-    char longbuffer[STRINGSIZE * 2];
+    char longbuffer[STRINGSIZE];
 
     if (!(pwp = getpwuid(uid)))
     {
@@ -573,38 +573,47 @@ FascistGecos(password, uid)
     {
 	for (i = 0; i < j; i++)
 	{
-	    strcpy(longbuffer, uwords[i]);
-	    strcat(longbuffer, uwords[j]);
-
-	    if (GTry(longbuffer, password))
+	    if (strlen(uwords[i]) + strlen(uwords[j]) < STRINGSIZE)
 	    {
-		return ("it is derived from your password entry");
-	    }
-
-	    strcpy(longbuffer, uwords[j]);
-	    strcat(longbuffer, uwords[i]);
+		strcpy(longbuffer, uwords[i]);
+		strcat(longbuffer, uwords[j]);
 
-	    if (GTry(longbuffer, password))
-	    {
-		return ("it's derived from your password entry");
+		if (GTry(longbuffer, password))
+		{
+		    return ("it is derived from your password entry");
+		}
+
+		strcpy(longbuffer, uwords[j]);
+		strcat(longbuffer, uwords[i]);
+
+		if (GTry(longbuffer, password))
+		{
+		    return ("it's derived from your password entry");
+		}
 	    }
 
-	    longbuffer[0] = uwords[i][0];
-	    longbuffer[1] = '\0';
-	    strcat(longbuffer, uwords[j]);
-
-	    if (GTry(longbuffer, password))
+	    if (strlen(uwords[j]) < STRINGSIZE - 1)
 	    {
-		return ("it is derivable from your password entry");
+		longbuffer[0] = uwords[i][0];
+		longbuffer[1] = '\0';
+		strcat(longbuffer, uwords[j]);
+
+		if (GTry(longbuffer, password))
+		{
+		    return ("it is derivable from your password entry");
+		}
 	    }
 
-	    longbuffer[0] = uwords[j][0];
-	    longbuffer[1] = '\0';
-	    strcat(longbuffer, uwords[i]);
-
-	    if (GTry(longbuffer, password))
+	    if (strlen(uwords[i]) < STRINGSIZE - 1)
 	    {
-		return ("it's derivable from your password entry");
+		longbuffer[0] = uwords[j][0];
+		longbuffer[1] = '\0';
+		strcat(longbuffer, uwords[i]);
+
+		if (GTry(longbuffer, password))
+		{
+		    return ("it's derivable from your password entry");
+		}
 	    }
 	}
     }