get_exp_type(const gchar *s) {
    /* variables */
    if(*(s+1) == '(')
        return EXP_EXPR;
    else if(*(s+1) == '{')
        return EXP_BRACED_VAR;
    else if(*(s+1) == '<')
        return EXP_JS;
    else if(*(s+1) == '[')
        return EXP_ESCAPE;
    else
        return EXP_SIMPLE_VAR;

    /*@notreached@*/
return EXP_ERR;
}

/*
 * recurse == 1: don't expand '@(command)@'
 * recurse == 2: don't expand '@<java script>@'
*/
gchar *
expand(const char *s, guint recurse) {
    uzbl_cmdprop *c;
    enum exp_type etype;
    char *end_simple_var = "^°!\"§$%&/()=?'`'+~*'#-.:,;@<>| \\{}[]¹²³¼½";
    char *ret = NULL;
    char *vend = NULL;
    GError *err = NULL;
    gchar *cmd_stdout = NULL;
    gchar *mycmd = NULL;
    GString *buf = g_string_new("");
    GString *js_ret = g_string_new("");

    while(s && *s) {
        switch(*s) {
            case '\\':
                g_string_append_c(buf, *++s);
                s++;
                break;

            case '@':
                etype = get_exp_type(s);
                s++;

                switch(etype) {
                    case EXP_SIMPLE_VAR:
                        vend = strpbrk(s, end_simple_var);
                        if(!vend) vend = strchr(s, '\0');
                        break;
                    case EXP_BRACED_VAR:
                        s++;
                        vend = strchr(s, '}');
                        if(!vend) vend = strchr(s, '\0');
                        break;
                    case EXP_EXPR:
                        s++;
                        vend = strstr(s, ")@");
                        if(!vend) vend = strchr(s, '\0');
                        break;
                    case EXP_JS:
                        s++;
                        vend = strstr(s, ">@");
                        if(!vend) vend = strchr(s, '\0');
                        break;
                    case EXP_ESCAPE:
                        s++;
                        vend = strstr(s, "]@");
                        if(!vend) vend = strchr(s, '\0');
                        break;
                    /*@notreached@*/
                    case EXP_ERR:
                        break;
                }
                assert(vend);

                ret = g_strndup(s, vend-s);

                if(etype == EXP_SIMPLE_VAR ||
                   etype == EXP_BRACED_VAR) {
                    if( (c = g_hash_table_lookup(uzbl.comm.proto_var, ret)) ) {
                        if(c->type == TYPE_STR && *c->ptr.s != NULL) {
                            g_string_append(buf, (gchar *)*c->ptr.s);
                        }
                        else if(c->type == TYPE_INT) {
                            g_string_append_printf(buf, "%d", *c->ptr.i);
                        }
                        else if(c->type == TYPE_FLOAT) {
                            g_string_append_printf(buf, "%f", *c->ptr.f);
                        }
                    }

                    if(etype == EXP_SIMPLE_VAR)
                        s = vend;
                    else
                        s = vend+1;
                }
                else if(recurse != 1 &&
                        etype == EXP_EXPR) {

                    /* execute program directly */
                    if(ret[0] == '+') {
                        mycmd = expand(ret+1, 1);
                        g_spawn_command_line_sync(mycmd, &cmd_stdout, NULL, NULL, &err);
                        g_free(mycmd);
                    }
                    /* execute program through shell, quote it first */
                    else {
                        mycmd = expand(ret, 1);
                        gchar *quoted = g_shell_quote(mycmd);
                        gchar *tmp = g_strdup_printf("%s %s",
                                uzbl.behave.shell_cmd?uzbl.behave.shell_cmd:"/bin/sh -c",
                                quoted);
                        g_spawn_command_line_sync(tmp, &cmd_stdout, NULL, NULL, &err);
                        g_free(mycmd);
                        g_free(quoted);
                        g_free(tmp);
                    }

                    if (err) {
                        g_printerr("error on running command: %s\n", err->message);
                        g_error_free (err);
                    }
                    else if (*cmd_stdout) {
                        size_t len = strlen(cmd_stdout);

                        if(len > 0 && cmd_stdout[len-1] == '\n')
                            cmd_stdout[--len] = '\0'; /* strip trailing newline */

                        g_string_append(buf, cmd_stdout);
                        g_free(cmd_stdout);
                    }
                    s = vend+2;
                }
                else if(recurse != 2 &&
                        etype == EXP_JS) {

                    /* read JS from file */
                    if(ret[0] == '+') {
                        GArray *tmp = g_array_new(TRUE, FALSE, sizeof(gchar *));
                        mycmd = expand(ret+1, 2);
                        g_array_append_val(tmp, mycmd);

                        run_external_js(uzbl.gui.web_view, tmp, js_ret);
                        g_array_free(tmp, TRUE);
                    }
                    /* JS from string */
                    else {
                        mycmd = expand(ret, 2);
                        eval_js(uzbl.gui.web_view, mycmd, js_ret);
                        g_free(mycmd);
                    }

                    if(js_ret->str) {
                        g_string_append(buf, js_ret->str);
                        g_string_free(js_ret, TRUE);
                        js_ret = g_string_new("");
                    }
                    s = vend+2;
                }
                else if(etype == EXP_ESCAPE) {
                    mycmd = expand(ret, 0);
                    char *escaped = g_markup_escape_text(mycmd, strlen(mycmd));

                    g_string_append(buf, escaped);

                    g_free(escaped);
                    g_free(mycmd);
                    s = vend+2;
                }

                g_free(ret);
                ret = NULL;
                break;

            default:
                g_string_append_c(buf, *s);
                s++;
                break;
        }
    }
    g_string_free(js_ret, TRUE);
    return g_string_free(buf, FALSE);
}

This category addresses vulnerabilities caused by flawed access control mechanisms, where incorrect permission settings allow unauthorized users to access restricted resources.