Mixing
How to retrieve the file that is outside of current directory using format specifier?
up vote
-2
down vote
favorite
char * read_file(char * filename) {
char * file_contents = malloc(4096 * sizeof(char));
FILE * file;
file = fopen(filename, "r");
fread(file_contents, 4096, sizeof(char), file);
fclose(file);
return file_contents;
}
char * read_flag() {
return read_file("/flag.txt"); // outside of current working directory ;)
}
int main(int argc, char* argv) {
setvbuf(stdin, NULL, _IONBF, 0);
setvbuf(stdout, NULL, _IONBF, 0);
char * flag = read_flag();
char input_filename[40];
//Current directory is /home/problem
printf("Current working directory is: ");
system("pwd");
printf("Enter a filename to print the contents of the file => ");
scanf("%39s", input_filename);
while ((directory_entry = readdir(directory)) != NULL) {
if (strcmp(input_filename, directory_entry->d_name) == 0) {
printf("File contents:n");
printf("%sn", read_file(input_filename));
return 0;
}
}
}
I need to open a file that is outside of this directory ("/flag.txt"). I have tried something like "../" in the input to get out from this directory but it is not working. I am not sure how do i enter the filename such that it can retrieve the file that is outside of the /home/problem directory. I am currently using Ubuntu to do this. I think the idea should be using something like %s%d when i enter my input. Is this possible to use any specifier or exploit this program in order to read the entire contents?
c file code-injection format-specifiers
edited 2 days ago
mrflash818
6301018
asked 2 days ago
Y.M
277
add a comment |
up vote
-2
down vote
favorite
char * read_file(char * filename) {
char * file_contents = malloc(4096 * sizeof(char));
FILE * file;
file = fopen(filename, "r");
fread(file_contents, 4096, sizeof(char), file);
fclose(file);
return file_contents;
}
char * read_flag() {
return read_file("/flag.txt"); // outside of current working directory ;)
}
int main(int argc, char* argv) {
setvbuf(stdin, NULL, _IONBF, 0);
setvbuf(stdout, NULL, _IONBF, 0);
char * flag = read_flag();
char input_filename[40];
//Current directory is /home/problem
printf("Current working directory is: ");
system("pwd");
printf("Enter a filename to print the contents of the file => ");
scanf("%39s", input_filename);
while ((directory_entry = readdir(directory)) != NULL) {
if (strcmp(input_filename, directory_entry->d_name) == 0) {
printf("File contents:n");
printf("%sn", read_file(input_filename));
return 0;
}
}
}
I need to open a file that is outside of this directory ("/flag.txt"). I have tried something like "../" in the input to get out from this directory but it is not working. I am not sure how do i enter the filename such that it can retrieve the file that is outside of the /home/problem directory. I am currently using Ubuntu to do this. I think the idea should be using something like %s%d when i enter my input. Is this possible to use any specifier or exploit this program in order to read the entire contents?
c file code-injection format-specifiers
edited 2 days ago
mrflash818
6301018
asked 2 days ago
Y.M
277
Where does SQL come into play here?!
– Corion
2 days ago
You know what./means? you know what it refers to ? BTW: in your progam fragmentdirectoryis never defined nor initialized.
– joop
2 days ago
@joop sorry i typo. Supposed to be /flag.txt without the "."
– Y.M
2 days ago
add a comment |
up vote
-2
down vote
favorite
up vote
-2
down vote
favorite
char * read_file(char * filename) {
char * file_contents = malloc(4096 * sizeof(char));
FILE * file;
file = fopen(filename, "r");
fread(file_contents, 4096, sizeof(char), file);
fclose(file);
return file_contents;
}
char * read_flag() {
return read_file("/flag.txt"); // outside of current working directory ;)
}
int main(int argc, char* argv) {
setvbuf(stdin, NULL, _IONBF, 0);
setvbuf(stdout, NULL, _IONBF, 0);
char * flag = read_flag();
char input_filename[40];
//Current directory is /home/problem
printf("Current working directory is: ");
system("pwd");
printf("Enter a filename to print the contents of the file => ");
scanf("%39s", input_filename);
while ((directory_entry = readdir(directory)) != NULL) {
if (strcmp(input_filename, directory_entry->d_name) == 0) {
printf("File contents:n");
printf("%sn", read_file(input_filename));
return 0;
}
}
}
I need to open a file that is outside of this directory ("/flag.txt"). I have tried something like "../" in the input to get out from this directory but it is not working. I am not sure how do i enter the filename such that it can retrieve the file that is outside of the /home/problem directory. I am currently using Ubuntu to do this. I think the idea should be using something like %s%d when i enter my input. Is this possible to use any specifier or exploit this program in order to read the entire contents?
c file code-injection format-specifiers
edited 2 days ago
mrflash818
6301018
asked 2 days ago
Y.M
277
char * read_file(char * filename) {
char * file_contents = malloc(4096 * sizeof(char));
FILE * file;
file = fopen(filename, "r");
fread(file_contents, 4096, sizeof(char), file);
fclose(file);
return file_contents;
}
char * read_flag() {
return read_file("/flag.txt"); // outside of current working directory ;)
}
int main(int argc, char* argv) {
setvbuf(stdin, NULL, _IONBF, 0);
setvbuf(stdout, NULL, _IONBF, 0);
char * flag = read_flag();
char input_filename[40];
//Current directory is /home/problem
printf("Current working directory is: ");
system("pwd");
printf("Enter a filename to print the contents of the file => ");
scanf("%39s", input_filename);
while ((directory_entry = readdir(directory)) != NULL) {
if (strcmp(input_filename, directory_entry->d_name) == 0) {
printf("File contents:n");
printf("%sn", read_file(input_filename));
return 0;
}
}
}
I need to open a file that is outside of this directory ("/flag.txt"). I have tried something like "../" in the input to get out from this directory but it is not working. I am not sure how do i enter the filename such that it can retrieve the file that is outside of the /home/problem directory. I am currently using Ubuntu to do this. I think the idea should be using something like %s%d when i enter my input. Is this possible to use any specifier or exploit this program in order to read the entire contents?
c file code-injection format-specifiers
c file code-injection format-specifiers
edited 2 days ago
mrflash818
6301018
asked 2 days ago
Y.M
277
edited 2 days ago
mrflash818
6301018
asked 2 days ago
Y.M
277
edited 2 days ago
mrflash818
6301018
edited 2 days ago
mrflash818
6301018
edited 2 days ago
mrflash818
6301018
6301018
asked 2 days ago
Y.M
277
asked 2 days ago
Y.M
277
asked 2 days ago
Y.M
277
277
Where does SQL come into play here?!
– Corion
2 days ago
You know what./means? you know what it refers to ? BTW: in your progam fragmentdirectoryis never defined nor initialized.
– joop
2 days ago
@joop sorry i typo. Supposed to be /flag.txt without the "."
– Y.M
2 days ago
add a comment |
Where does SQL come into play here?!
– Corion
2 days ago
You know what./means? you know what it refers to ? BTW: in your progam fragmentdirectoryis never defined nor initialized.
– joop
2 days ago
@joop sorry i typo. Supposed to be /flag.txt without the "."
– Y.M
2 days ago
Where does SQL come into play here?!
– Corion
2 days ago
Where does SQL come into play here?!
– Corion
2 days ago
You know what
./ means? you know what it refers to ? BTW: in your progam fragment directory is never defined nor initialized.– joop
2 days ago
You know what
./ means? you know what it refers to ? BTW: in your progam fragment directory is never defined nor initialized.– joop
2 days ago
@joop sorry i typo. Supposed to be /flag.txt without the "."
– Y.M
2 days ago
@joop sorry i typo. Supposed to be /flag.txt without the "."
– Y.M
2 days ago
add a comment |
2 Answers
2
active
oldest
votes
up vote
1
down vote
You need to pass the full path to your file if it is outside the solution directory either with \ or one /. On a windows based system this would be for example C:\folder\file.txt. I do not use linux currently, but it should be /home/folder/file.txt.
answered 2 days ago
ats
594
For an absolute pathname, add a leading slash:/home/folder/file.txt.
– joop
2 days ago
@joop The current directory when i execute the code is /home/problem. However the file that i want to access is outside of this directory which is ./flag.txt
– Y.M
2 days ago
@Y.M. You can't refer to ./flag.txt without knowing the current directory, since the first part./means "in the current directory". So when you say it is outside/home/problem, and the name is./file.txt, noone can know where that file is. Find out which directoryflag.txtis in. Say e.g. it is the folder/somwhere/else/, then you just open/somwhere/else/flag.txt
– nos
2 days ago
add a comment |
up vote
0
down vote
The fopen function can fail, and you should handle that. Read fopen(3), open(2), path_resolution(7), errno(3) to understand the possible failure reasons. Details could be file system and computer specific (and could include hardware failures).
I recommend using perror(3) and exit(3) on failure (don't forget to include both <stdio.h> for perror and <stdlib.h> for exit):
FILE* file = fopen(filename, "r");
if (!file) {
perror(filename);
exit(EXIT_FAILURE);
}
then you'll get a meaningful error message (into stderr) on failure
My guess: your root file system (and root directory / ...) don't have a flag.txt file and you might want to retrieve what your shell understands from ~/flag.txt. Perhaps you want to retrieve it in your home directory (then build its file path, using getenv("HOME") on Linux or Unix; see this).
Read also about globbing, and glob(7).
Read also some Linux programming book, perhaps the old ALP.
answered 2 days ago
Basile Starynkevitch
174k13163357
Why the fopen function will fail?
– Y.M
2 days ago
There are many failure reasons. Read the various links. And since the failure is not depending upon just your program, but upon the whole system state of your entire computer, you always should handle it. You cannot reasonably predict the state of the computer running your program. I'll guess that your Linux computer don't have any/flag.txt(because the root directory/is not yours, and hier(7) don't document that it should have aflag.txtfile)
– Basile Starynkevitch
yesterday
add a comment |
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
1
down vote
You need to pass the full path to your file if it is outside the solution directory either with \ or one /. On a windows based system this would be for example C:\folder\file.txt. I do not use linux currently, but it should be /home/folder/file.txt.
answered 2 days ago
ats
594
For an absolute pathname, add a leading slash:/home/folder/file.txt.
– joop
2 days ago
@joop The current directory when i execute the code is /home/problem. However the file that i want to access is outside of this directory which is ./flag.txt
– Y.M
2 days ago
@Y.M. You can't refer to ./flag.txt without knowing the current directory, since the first part./means "in the current directory". So when you say it is outside/home/problem, and the name is./file.txt, noone can know where that file is. Find out which directoryflag.txtis in. Say e.g. it is the folder/somwhere/else/, then you just open/somwhere/else/flag.txt
– nos
2 days ago
add a comment |
up vote
1
down vote
You need to pass the full path to your file if it is outside the solution directory either with \ or one /. On a windows based system this would be for example C:\folder\file.txt. I do not use linux currently, but it should be /home/folder/file.txt.
answered 2 days ago
ats
594
For an absolute pathname, add a leading slash:/home/folder/file.txt.
– joop
2 days ago
@joop The current directory when i execute the code is /home/problem. However the file that i want to access is outside of this directory which is ./flag.txt
– Y.M
2 days ago
@Y.M. You can't refer to ./flag.txt without knowing the current directory, since the first part./means "in the current directory". So when you say it is outside/home/problem, and the name is./file.txt, noone can know where that file is. Find out which directoryflag.txtis in. Say e.g. it is the folder/somwhere/else/, then you just open/somwhere/else/flag.txt
– nos
2 days ago
add a comment |
up vote
1
down vote
up vote
1
down vote
You need to pass the full path to your file if it is outside the solution directory either with \ or one /. On a windows based system this would be for example C:\folder\file.txt. I do not use linux currently, but it should be /home/folder/file.txt.
answered 2 days ago
ats
594
You need to pass the full path to your file if it is outside the solution directory either with \ or one /. On a windows based system this would be for example C:\folder\file.txt. I do not use linux currently, but it should be /home/folder/file.txt.
answered 2 days ago
ats
594
edited 2 days ago
answered 2 days ago
ats
594
answered 2 days ago
ats
594
answered 2 days ago
ats
594
594
For an absolute pathname, add a leading slash:/home/folder/file.txt.
– joop
2 days ago
@joop The current directory when i execute the code is /home/problem. However the file that i want to access is outside of this directory which is ./flag.txt
– Y.M
2 days ago
@Y.M. You can't refer to ./flag.txt without knowing the current directory, since the first part./means "in the current directory". So when you say it is outside/home/problem, and the name is./file.txt, noone can know where that file is. Find out which directoryflag.txtis in. Say e.g. it is the folder/somwhere/else/, then you just open/somwhere/else/flag.txt
– nos
2 days ago
add a comment |
For an absolute pathname, add a leading slash:/home/folder/file.txt.
– joop
2 days ago
@joop The current directory when i execute the code is /home/problem. However the file that i want to access is outside of this directory which is ./flag.txt
– Y.M
2 days ago
@Y.M. You can't refer to ./flag.txt without knowing the current directory, since the first part./means "in the current directory". So when you say it is outside/home/problem, and the name is./file.txt, noone can know where that file is. Find out which directoryflag.txtis in. Say e.g. it is the folder/somwhere/else/, then you just open/somwhere/else/flag.txt
– nos
2 days ago
For an absolute pathname, add a leading slash:
/home/folder/file.txt.– joop
2 days ago
For an absolute pathname, add a leading slash:
/home/folder/file.txt.– joop
2 days ago
@joop The current directory when i execute the code is /home/problem. However the file that i want to access is outside of this directory which is ./flag.txt
– Y.M
2 days ago
@joop The current directory when i execute the code is /home/problem. However the file that i want to access is outside of this directory which is ./flag.txt
– Y.M
2 days ago
@Y.M. You can't refer to ./flag.txt without knowing the current directory, since the first part
./ means "in the current directory". So when you say it is outside /home/problem, and the name is ./file.txt , noone can know where that file is. Find out which directory flag.txt is in. Say e.g. it is the folder /somwhere/else/ , then you just open /somwhere/else/flag.txt– nos
2 days ago
@Y.M. You can't refer to ./flag.txt without knowing the current directory, since the first part
./ means "in the current directory". So when you say it is outside /home/problem, and the name is ./file.txt , noone can know where that file is. Find out which directory flag.txt is in. Say e.g. it is the folder /somwhere/else/ , then you just open /somwhere/else/flag.txt– nos
2 days ago
add a comment |
up vote
0
down vote
The fopen function can fail, and you should handle that. Read fopen(3), open(2), path_resolution(7), errno(3) to understand the possible failure reasons. Details could be file system and computer specific (and could include hardware failures).
I recommend using perror(3) and exit(3) on failure (don't forget to include both <stdio.h> for perror and <stdlib.h> for exit):
FILE* file = fopen(filename, "r");
if (!file) {
perror(filename);
exit(EXIT_FAILURE);
}
then you'll get a meaningful error message (into stderr) on failure
My guess: your root file system (and root directory / ...) don't have a flag.txt file and you might want to retrieve what your shell understands from ~/flag.txt. Perhaps you want to retrieve it in your home directory (then build its file path, using getenv("HOME") on Linux or Unix; see this).
Read also about globbing, and glob(7).
Read also some Linux programming book, perhaps the old ALP.
answered 2 days ago
Basile Starynkevitch
174k13163357
Why the fopen function will fail?
– Y.M
2 days ago
There are many failure reasons. Read the various links. And since the failure is not depending upon just your program, but upon the whole system state of your entire computer, you always should handle it. You cannot reasonably predict the state of the computer running your program. I'll guess that your Linux computer don't have any/flag.txt(because the root directory/is not yours, and hier(7) don't document that it should have aflag.txtfile)
– Basile Starynkevitch
yesterday
add a comment |
up vote
0
down vote
The fopen function can fail, and you should handle that. Read fopen(3), open(2), path_resolution(7), errno(3) to understand the possible failure reasons. Details could be file system and computer specific (and could include hardware failures).
I recommend using perror(3) and exit(3) on failure (don't forget to include both <stdio.h> for perror and <stdlib.h> for exit):
FILE* file = fopen(filename, "r");
if (!file) {
perror(filename);
exit(EXIT_FAILURE);
}
then you'll get a meaningful error message (into stderr) on failure
My guess: your root file system (and root directory / ...) don't have a flag.txt file and you might want to retrieve what your shell understands from ~/flag.txt. Perhaps you want to retrieve it in your home directory (then build its file path, using getenv("HOME") on Linux or Unix; see this).
Read also about globbing, and glob(7).
Read also some Linux programming book, perhaps the old ALP.
answered 2 days ago
Basile Starynkevitch
174k13163357
Why the fopen function will fail?
– Y.M
2 days ago
There are many failure reasons. Read the various links. And since the failure is not depending upon just your program, but upon the whole system state of your entire computer, you always should handle it. You cannot reasonably predict the state of the computer running your program. I'll guess that your Linux computer don't have any/flag.txt(because the root directory/is not yours, and hier(7) don't document that it should have aflag.txtfile)
– Basile Starynkevitch
yesterday
add a comment |
up vote
0
down vote
up vote
0
down vote
The fopen function can fail, and you should handle that. Read fopen(3), open(2), path_resolution(7), errno(3) to understand the possible failure reasons. Details could be file system and computer specific (and could include hardware failures).
I recommend using perror(3) and exit(3) on failure (don't forget to include both <stdio.h> for perror and <stdlib.h> for exit):
FILE* file = fopen(filename, "r");
if (!file) {
perror(filename);
exit(EXIT_FAILURE);
}
then you'll get a meaningful error message (into stderr) on failure
My guess: your root file system (and root directory / ...) don't have a flag.txt file and you might want to retrieve what your shell understands from ~/flag.txt. Perhaps you want to retrieve it in your home directory (then build its file path, using getenv("HOME") on Linux or Unix; see this).
Read also about globbing, and glob(7).
Read also some Linux programming book, perhaps the old ALP.
answered 2 days ago
Basile Starynkevitch
174k13163357
The fopen function can fail, and you should handle that. Read fopen(3), open(2), path_resolution(7), errno(3) to understand the possible failure reasons. Details could be file system and computer specific (and could include hardware failures).
I recommend using perror(3) and exit(3) on failure (don't forget to include both <stdio.h> for perror and <stdlib.h> for exit):
FILE* file = fopen(filename, "r");
if (!file) {
perror(filename);
exit(EXIT_FAILURE);
}
then you'll get a meaningful error message (into stderr) on failure
My guess: your root file system (and root directory / ...) don't have a flag.txt file and you might want to retrieve what your shell understands from ~/flag.txt. Perhaps you want to retrieve it in your home directory (then build its file path, using getenv("HOME") on Linux or Unix; see this).
Read also about globbing, and glob(7).
Read also some Linux programming book, perhaps the old ALP.
answered 2 days ago
Basile Starynkevitch
174k13163357
edited yesterday
answered 2 days ago
Basile Starynkevitch
174k13163357
answered 2 days ago
Basile Starynkevitch
174k13163357
answered 2 days ago
Basile Starynkevitch
174k13163357
174k13163357
Why the fopen function will fail?
– Y.M
2 days ago
There are many failure reasons. Read the various links. And since the failure is not depending upon just your program, but upon the whole system state of your entire computer, you always should handle it. You cannot reasonably predict the state of the computer running your program. I'll guess that your Linux computer don't have any/flag.txt(because the root directory/is not yours, and hier(7) don't document that it should have aflag.txtfile)
– Basile Starynkevitch
yesterday
add a comment |
Why the fopen function will fail?
– Y.M
2 days ago
There are many failure reasons. Read the various links. And since the failure is not depending upon just your program, but upon the whole system state of your entire computer, you always should handle it. You cannot reasonably predict the state of the computer running your program. I'll guess that your Linux computer don't have any/flag.txt(because the root directory/is not yours, and hier(7) don't document that it should have aflag.txtfile)
– Basile Starynkevitch
yesterday
Why the fopen function will fail?
– Y.M
2 days ago
Why the fopen function will fail?
– Y.M
2 days ago
There are many failure reasons. Read the various links. And since the failure is not depending upon just your program, but upon the whole system state of your entire computer, you always should handle it. You cannot reasonably predict the state of the computer running your program. I'll guess that your Linux computer don't have any
/flag.txt (because the root directory / is not yours, and hier(7) don't document that it should have a flag.txt file)– Basile Starynkevitch
yesterday
There are many failure reasons. Read the various links. And since the failure is not depending upon just your program, but upon the whole system state of your entire computer, you always should handle it. You cannot reasonably predict the state of the computer running your program. I'll guess that your Linux computer don't have any
/flag.txt (because the root directory / is not yours, and hier(7) don't document that it should have a flag.txt file)– Basile Starynkevitch
yesterday
add a comment |
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53370781%2fhow-to-retrieve-the-file-that-is-outside-of-current-directory-using-format-speci%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Where does SQL come into play here?!
– Corion
2 days ago
You know what
./means? you know what it refers to ? BTW: in your progam fragmentdirectoryis never defined nor initialized.– joop
2 days ago
@joop sorry i typo. Supposed to be /flag.txt without the "."
– Y.M
2 days ago