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How to prevent LD_PRELOAD on a binary?


By : 0xEC108
Date : August 02 2020, 12:00 AM
around this issue Just like scripts have an interpreter specified via the #! mechanism, excecutables work similarly. ELF executables have a field in the program header whose type is PT_INTERP and it gives a path to an "interpreter" for the executable. That "interpreter" is the dynamic linker, ld-linux.so. That linker will process the header and map the file into memory and all the rest.
It is this ld-linux.so loader that implements the LD_PRELOAD feature.
code :


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LD_PRELOAD affects new child even after unsetenv("LD_PRELOAD")


By : Angel Barrientos Cru
Date : March 29 2020, 07:55 AM
help you fix your problem edit: so the problem/question actually was: howcome can't you unset LD_PRELOAD reliably using a preloaded main_init() from within bash.
The reason is that execve, which is called after you popen, takes the environment from (probably)
code :
extern char **environ;
extern char**environ;

int  __attribute__((constructor))  main_init(void)
{
int i;
printf("Unsetting LD_PRELOAD: %x\n",unsetenv("LD_PRELOAD"));
printf("LD_PRELOAD: \"%s\"\n",getenv("LD_PRELOAD"));
printf("Environ: %lx\n",environ);
printf("unsetenv: %lx\n",unsetenv);
for (i=0;environ[i];i++ ) printf("env: %s\n",environ[i]);
fflush(stdout);
FILE *fp = popen("ls", "r");
pclose(fp);
}
unsetenv: 7f4c78fd5290
unsetenv: 7f1127317290
unsetenv: 7f1ab63a2290
unsetenv: 46d170
for (i=0;environ[i];i++ )
{
    if ( strstr(environ[i],"LD_PRELOAD=") )
    {
         printf("hacking out LD_PRELOAD from environ[%d]\n",i);
         environ[i][0] = 'D';
    }
}
execve("/bin/sh", ["sh", "-c", "ls"], [... "DD_PRELOAD=mylib.so" ...]) = 0

Prevent from reverse engineering C++ binary


By : Bin Sun
Date : March 29 2020, 07:55 AM
This might help you If I got you right, you are talking about obfuscation.
This question on Stackoverflow covers the topic. There is a lot of software that obfuscates C++ code, quick googling shows a lot of such apps, e.g. this or this.

Is there a git hook which can prevent binary check-ins


By : pulkit bhardwaj
Date : March 29 2020, 07:55 AM
help you fix your problem I don't know of an existing hook, but git already comes with a hook that checks for adding "non-ascii names", as a sample pre-commit hook. This will likely already be in your existing git repositories as .git/hooks/pre-commit.sample.
Using that hook as a template and considering the answers to "How to determine if Git handles a file as binary or as text?", you could do something like this (see "git's semi-secret empty tree" for where EMPTY_TREE comes from):
code :
#! /bin/sh

stop_binaries=$(git config --get hooks.stop_binaries)

exec 1>&2

if [ "$stop_binaries" = true ]; then
    EMPTY_TREE=$(git hash-object -t tree /dev/null)
    # or: EMPTY_TREE=4b825dc642cb6eb9a060e54bf8d69288fbee4904
    if git diff --cached --numstat $EMPTY_TREE | grep -e '^-' >/dev/null; then
        echo Error: commit would add binary files:
        git diff --cached --numstat $EMPTY_TREE | grep -e '^-' | cut -f3-
        exit 1
    fi
fi

LD_PRELOAD with setuid binary


By : Divya Theodore
Date : March 29 2020, 07:55 AM
hope this fix your issue LD_PRELOAD cannot be used with setuid. This is a security feature in linux. For reference check this article, which goes into the detail on how to use LD_PRELOAD to substitute some library calls with custom code, at the example of malloc.

How to prevent LD_PRELOAD or ld.so.preload configuration?


By : kevinliu
Date : March 29 2020, 07:55 AM
Hope that helps
is it possible to prevent/detect preloaded library, either through LD_PRELOAD environment variable or through /etc/ld.so.preload configuration?
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