static void _php_mb_regex_ereg_replace_exec(INTERNAL_FUNCTION_PARAMETERS, OnigOptionType options, int is_callable)
{
	zval **arg_pattern_zval;

	char *arg_pattern;
	int arg_pattern_len;

	char *replace;
	int replace_len;

	zend_fcall_info arg_replace_fci;
	zend_fcall_info_cache arg_replace_fci_cache;

	char *string;
	int string_len;

	char *p;
	php_mb_regex_t *re;
	OnigSyntaxType *syntax;
	OnigRegion *regs = NULL;
	smart_str out_buf = { 0 };
	smart_str eval_buf = { 0 };
	smart_str *pbuf;
	int i, err, eval, n;
	OnigUChar *pos;
	OnigUChar *string_lim;
	char *description = NULL;
	char pat_buf[2];

	const mbfl_encoding *enc;

	{
		const char *current_enc_name;
		current_enc_name = _php_mb_regex_mbctype2name(MBREX(current_mbctype));
		if (current_enc_name == NULL ||
			(enc = mbfl_name2encoding(current_enc_name)) == NULL) {
			php_error_docref(NULL TSRMLS_CC, E_WARNING, "Unknown error");
			RETURN_FALSE;
		}
	}
	eval = 0;
	{
		char *option_str = NULL;
		int option_str_len = 0;

		if (!is_callable) {
			if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "Zss|s",
						&arg_pattern_zval,
						&replace, &replace_len,
						&string, &string_len,
						&option_str, &option_str_len) == FAILURE) {
				RETURN_FALSE;
			}
		} else {
			if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "Zfs|s",
						&arg_pattern_zval,
						&arg_replace_fci, &arg_replace_fci_cache,
						&string, &string_len,
						&option_str, &option_str_len) == FAILURE) {
				RETURN_FALSE;
			}
		}

		if (option_str != NULL) {
			_php_mb_regex_init_options(option_str, option_str_len, &options, &syntax, &eval);
		} else {
			options |= MBREX(regex_default_options);
			syntax = MBREX(regex_default_syntax);
		}
	}
	if (Z_TYPE_PP(arg_pattern_zval) == IS_STRING) {
		arg_pattern = Z_STRVAL_PP(arg_pattern_zval);
		arg_pattern_len = Z_STRLEN_PP(arg_pattern_zval);
 	} else {
 		/* FIXME: this code is not multibyte aware! */
 		convert_to_long_ex(arg_pattern_zval);
		pat_buf[0] = (char)Z_LVAL_PP(arg_pattern_zval);	
 		pat_buf[1] = '\0';
 
 		arg_pattern = pat_buf;
		arg_pattern_len = 1;	
 	}
 	/* create regex pattern buffer */
 	re = php_mbregex_compile_pattern(arg_pattern, arg_pattern_len, options, MBREX(current_mbctype), syntax TSRMLS_CC);
	if (re == NULL) {
		RETURN_FALSE;
	}

	if (eval || is_callable) {
		pbuf = &eval_buf;
		description = zend_make_compiled_string_description("mbregex replace" TSRMLS_CC);
	} else {
		pbuf = &out_buf;
		description = NULL;
	}

	if (is_callable) {
		if (eval) {
			php_error_docref(NULL TSRMLS_CC, E_WARNING, "Option 'e' cannot be used with replacement callback");
			RETURN_FALSE;
		}
	}

	/* do the actual work */
	err = 0;
	pos = (OnigUChar *)string;
	string_lim = (OnigUChar*)(string + string_len);
	regs = onig_region_new();
	while (err >= 0) {
		err = onig_search(re, (OnigUChar *)string, (OnigUChar *)string_lim, pos, (OnigUChar *)string_lim, regs, 0);
		if (err <= -2) {
			OnigUChar err_str[ONIG_MAX_ERROR_MESSAGE_LEN];
			onig_error_code_to_str(err_str, err);
			php_error_docref(NULL TSRMLS_CC, E_WARNING, "mbregex search failure in php_mbereg_replace_exec(): %s", err_str);
			break;
		}
		if (err >= 0) {
#if moriyoshi_0
			if (regs->beg[0] == regs->end[0]) {
				php_error_docref(NULL TSRMLS_CC, E_WARNING, "Empty regular expression");
				break;
			}
#endif
			/* copy the part of the string before the match */
			smart_str_appendl(&out_buf, pos, (size_t)((OnigUChar *)(string + regs->beg[0]) - pos));

			if (!is_callable) {
				/* copy replacement and backrefs */
				i = 0;
				p = replace;
				while (i < replace_len) {
					int fwd = (int) php_mb_mbchar_bytes_ex(p, enc);
					n = -1;
					if ((replace_len - i) >= 2 && fwd == 1 &&
					p[0] == '\\' && p[1] >= '0' && p[1] <= '9') {
						n = p[1] - '0';
					}
					if (n >= 0 && n < regs->num_regs) {
						if (regs->beg[n] >= 0 && regs->beg[n] < regs->end[n] && regs->end[n] <= string_len) {
							smart_str_appendl(pbuf, string + regs->beg[n], regs->end[n] - regs->beg[n]);
						}
						p += 2;
						i += 2;
					} else {
						smart_str_appendl(pbuf, p, fwd);
						p += fwd;
						i += fwd;
 					}
 				}
 			}
 			if (eval) {
 				zval v;
 				/* null terminate buffer */
				smart_str_0(&eval_buf);
				/* do eval */
				if (zend_eval_stringl(eval_buf.c, eval_buf.len, &v, description TSRMLS_CC) == FAILURE) {
					efree(description);
					php_error_docref(NULL TSRMLS_CC,E_ERROR, "Failed evaluating code: %s%s", PHP_EOL, eval_buf.c);
					/* zend_error() does not return in this case */
				}

				/* result of eval */
				convert_to_string(&v);
				smart_str_appendl(&out_buf, Z_STRVAL(v), Z_STRLEN(v));
				/* Clean up */
 				eval_buf.len = 0;
 				zval_dtor(&v);
 			} else if (is_callable) {
				zval *retval_ptr;
 				zval **args[1];
 				zval *subpats;
 				int i;
 				MAKE_STD_ZVAL(subpats);
 				array_init(subpats);
 				for (i = 0; i < regs->num_regs; i++) {
 					add_next_index_stringl(subpats, string + regs->beg[i], regs->end[i] - regs->beg[i], 1);
				}				
 				args[0] = &subpats;
 				/* null terminate buffer */
 				smart_str_0(&eval_buf);
 				arg_replace_fci.param_count = 1;
 				arg_replace_fci.params = args;
 				arg_replace_fci.retval_ptr_ptr = &retval_ptr;
				if (zend_call_function(&arg_replace_fci, &arg_replace_fci_cache TSRMLS_CC) == SUCCESS && arg_replace_fci.retval_ptr_ptr) {
 					convert_to_string_ex(&retval_ptr);
 					smart_str_appendl(&out_buf, Z_STRVAL_P(retval_ptr), Z_STRLEN_P(retval_ptr));
 					eval_buf.len = 0;
 					zval_ptr_dtor(&retval_ptr);
 				} else {
					efree(description);
 					if (!EG(exception)) {
 						php_error_docref(NULL TSRMLS_CC, E_WARNING, "Unable to call custom replacement function");
 					}
				}
				zval_ptr_dtor(&subpats);
			}

			n = regs->end[0];
			if ((pos - (OnigUChar *)string) < n) {
 				pos = (OnigUChar *)string + n;
 			} else {
 				if (pos < string_lim) {
					smart_str_appendl(&out_buf, pos, 1); 
 				}
 				pos++;
 			}
		} else { /* nomatch */
			/* stick that last bit of string on our output */
			if (string_lim - pos > 0) {
				smart_str_appendl(&out_buf, pos, string_lim - pos);
			}
		}
		onig_region_free(regs, 0);
	}

	if (description) {
		efree(description);
	}
	if (regs != NULL) {
		onig_region_free(regs, 1);
	}
 	smart_str_free(&eval_buf);
 
 	if (err <= -2) {
		smart_str_free(&out_buf);	
 		RETVAL_FALSE;
 	} else {
 		smart_str_appendc(&out_buf, '\0');
		RETVAL_STRINGL((char *)out_buf.c, out_buf.len - 1, 0);
	}
}

The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations.