From 9c20596400cef759ecc760e1b028fd1748e9be5d Mon Sep 17 00:00:00 2001 From: Corey Farrell Date: Sat, 1 Jul 2017 20:24:27 -0400 Subject: [PATCH] AST-2017-006: Fix app_minivm application MinivmNotify command injection An admin can configure app_minivm with an externnotify program to be run when a voicemail is received. The app_minivm application MinivmNotify uses ast_safe_system() for this purpose which is vulnerable to command injection since the Caller-ID name and number values given to externnotify can come from an external untrusted source. * Add ast_safe_execvp() function. This gives modules the ability to run external commands with greater safety compared to ast_safe_system(). Specifically when some parameters are filled by untrusted sources the new function does not allow malicious input to break argument encoding. This may be of particular concern where CALLERID(name) or CALLERID(num) may be used as a parameter to a script run by ast_safe_system() which could potentially allow arbitrary command execution. * Changed app_minivm.c:run_externnotify() to use the new ast_safe_execvp() instead of ast_safe_system() to avoid command injection. * Document code injection potential from untrusted data sources for other shell commands that are under user control. ASTERISK-27103 Change-Id: I7552472247a84cde24e1358aaf64af160107aef1 --- README-SERIOUSLY.bestpractices.txt | 7 +++ apps/app_minivm.c | 36 ++++++++---- apps/app_mixmonitor.c | 15 +++++ apps/app_system.c | 10 ++++ configs/samples/minivm.conf.sample | 2 +- funcs/func_shell.c | 5 ++ include/asterisk/app.h | 31 +++++++++- main/asterisk.c | 91 +++++++++++++++++++++++++----- res/res_monitor.c | 13 ++++- 9 files changed, 179 insertions(+), 31 deletions(-) diff --git a/README-SERIOUSLY.bestpractices.txt b/README-SERIOUSLY.bestpractices.txt index b6b418d9fa..0d3e670cf2 100644 --- a/README-SERIOUSLY.bestpractices.txt +++ b/README-SERIOUSLY.bestpractices.txt @@ -94,6 +94,13 @@ your ITSP in a place where you didn't expect to allow it. There are a couple of ways in which you can mitigate this impact: stricter pattern matching, or using the FILTER() dialplan function. +The CALLERID(num) and CALLERID(name) values are other commonly used values that +are sources of data potentially supplied by outside sources. If you use these +values as parameters to the System(), MixMonitor(), or Monitor() applications +or the SHELL() dialplan function, you can allow injection of arbitrary operating +system command execution. The FILTER() dialplan function is available to remove +dangerous characters from untrusted strings to block the command injection. + Strict Pattern Matching ----------------------- diff --git a/apps/app_minivm.c b/apps/app_minivm.c index 41fd5e77dd..6477460487 100644 --- a/apps/app_minivm.c +++ b/apps/app_minivm.c @@ -1776,21 +1776,35 @@ static int play_record_review(struct ast_channel *chan, char *playfile, char *re /*! \brief Run external notification for voicemail message */ static void run_externnotify(struct ast_channel *chan, struct minivm_account *vmu) { - char arguments[BUFSIZ]; + char fquser[AST_MAX_CONTEXT * 2]; + char *argv[5] = { NULL }; + struct ast_party_caller *caller; + char *cid; + int idx; - if (ast_strlen_zero(vmu->externnotify) && ast_strlen_zero(global_externnotify)) + if (ast_strlen_zero(vmu->externnotify) && ast_strlen_zero(global_externnotify)) { return; + } + + snprintf(fquser, sizeof(fquser), "%s@%s", vmu->username, vmu->domain); - snprintf(arguments, sizeof(arguments), "%s %s@%s %s %s&", - ast_strlen_zero(vmu->externnotify) ? global_externnotify : vmu->externnotify, - vmu->username, vmu->domain, - (ast_channel_caller(chan)->id.name.valid && ast_channel_caller(chan)->id.name.str) - ? ast_channel_caller(chan)->id.name.str : "", - (ast_channel_caller(chan)->id.number.valid && ast_channel_caller(chan)->id.number.str) - ? ast_channel_caller(chan)->id.number.str : ""); + caller = ast_channel_caller(chan); + idx = 0; + argv[idx++] = ast_strlen_zero(vmu->externnotify) ? global_externnotify : vmu->externnotify; + argv[idx++] = fquser; + cid = S_COR(caller->id.name.valid, caller->id.name.str, NULL); + if (cid) { + argv[idx++] = cid; + } + cid = S_COR(caller->id.number.valid, caller->id.number.str, NULL); + if (cid) { + argv[idx++] = cid; + } + argv[idx] = NULL; - ast_debug(1, "Executing: %s\n", arguments); - ast_safe_system(arguments); + ast_debug(1, "Executing: %s %s %s %s\n", + argv[0], argv[1], argv[2] ?: "", argv[3] ?: ""); + ast_safe_execvp(1, argv[0], argv); } /*!\internal diff --git a/apps/app_mixmonitor.c b/apps/app_mixmonitor.c index 8de4995afa..7fef15ebf8 100644 --- a/apps/app_mixmonitor.c +++ b/apps/app_mixmonitor.c @@ -138,6 +138,11 @@ ASTERISK_REGISTER_FILE() Will be executed when the recording is over. Any strings matching ^{X} will be unescaped to X. All variables will be evaluated at the time MixMonitor is called. + Do not use untrusted strings such as CALLERID(num) + or CALLERID(name) as part of the command parameters. You + risk a command injection attack executing arbitrary commands if the untrusted + strings aren't filtered to remove dangerous characters. See function + FILTER(). @@ -150,6 +155,11 @@ ASTERISK_REGISTER_FILE() Will contain the filename used to record. + Do not use untrusted strings such as CALLERID(num) + or CALLERID(name) as part of ANY of the application's + parameters. You risk a command injection attack executing arbitrary commands + if the untrusted strings aren't filtered to remove dangerous characters. See + function FILTER(). Monitor @@ -224,6 +234,11 @@ ASTERISK_REGISTER_FILE() Will be executed when the recording is over. Any strings matching ^{X} will be unescaped to X. All variables will be evaluated at the time MixMonitor is called. + Do not use untrusted strings such as CALLERID(num) + or CALLERID(name) as part of the command parameters. You + risk a command injection attack executing arbitrary commands if the untrusted + strings aren't filtered to remove dangerous characters. See function + FILTER(). diff --git a/apps/app_system.c b/apps/app_system.c index 7fcffb196a..74d33119f6 100644 --- a/apps/app_system.c +++ b/apps/app_system.c @@ -48,6 +48,11 @@ ASTERISK_REGISTER_FILE() Command to execute + Do not use untrusted strings such as CALLERID(num) + or CALLERID(name) as part of the command parameters. You + risk a command injection attack executing arbitrary commands if the untrusted + strings aren't filtered to remove dangerous characters. See function + FILTER(). @@ -73,6 +78,11 @@ ASTERISK_REGISTER_FILE() Command to execute + Do not use untrusted strings such as CALLERID(num) + or CALLERID(name) as part of the command parameters. You + risk a command injection attack executing arbitrary commands if the untrusted + strings aren't filtered to remove dangerous characters. See function + FILTER(). diff --git a/configs/samples/minivm.conf.sample b/configs/samples/minivm.conf.sample index 2df3449d13..79fdbb0e2c 100644 --- a/configs/samples/minivm.conf.sample +++ b/configs/samples/minivm.conf.sample @@ -51,7 +51,7 @@ silencethreshold=128 ; If you need to have an external program, i.e. /usr/bin/myapp called when a ; voicemail is received by the server. The arguments are ; -; +; ; ;externnotify=/usr/bin/myapp ; The character set for voicemail messages can be specified here diff --git a/funcs/func_shell.c b/funcs/func_shell.c index f529cbf724..c600c036e7 100644 --- a/funcs/func_shell.c +++ b/funcs/func_shell.c @@ -84,6 +84,11 @@ static int shell_helper(struct ast_channel *chan, const char *cmd, char *data, The command that the shell should execute. + Do not use untrusted strings such as CALLERID(num) + or CALLERID(name) as part of the command parameters. You + risk a command injection attack executing arbitrary commands if the untrusted + strings aren't filtered to remove dangerous characters. See function + FILTER(). diff --git a/include/asterisk/app.h b/include/asterisk/app.h index d86b63338f..0505a6b987 100644 --- a/include/asterisk/app.h +++ b/include/asterisk/app.h @@ -871,9 +871,34 @@ int ast_vm_test_destroy_user(const char *context, const char *mailbox); int ast_vm_test_create_user(const char *context, const char *mailbox); #endif -/*! \brief Safely spawn an external program while closing file descriptors - \note This replaces the \b system call in all Asterisk modules -*/ +/*! + * \brief Safely spawn an external program while closing file descriptors + * + * \note This replaces the \b execvp call in all Asterisk modules + * + * \param dualfork Non-zero to simulate running the program in the + * background by forking twice. The option provides similar + * functionality to the '&' in the OS shell command "cmd &". The + * option allows Asterisk to run a reaper loop to watch the first fork + * which immediately exits after spaning the second fork. The actual + * program is run in the second fork. + * \param file execvp(file, argv) file parameter + * \param argv execvp(file, argv) argv parameter + */ +int ast_safe_execvp(int dualfork, const char *file, char *const argv[]); + +/*! + * \brief Safely spawn an OS shell command while closing file descriptors + * + * \note This replaces the \b system call in all Asterisk modules + * + * \param s - OS shell command string to execute. + * + * \warning Command injection can happen using this call if the passed + * in string is created using untrusted data from an external source. + * It is best not to use untrusted data. However, the caller could + * filter out dangerous characters to avoid command injection. + */ int ast_safe_system(const char *s); /*! diff --git a/main/asterisk.c b/main/asterisk.c index 1e4772ea71..8931496f70 100644 --- a/main/asterisk.c +++ b/main/asterisk.c @@ -1214,11 +1214,10 @@ void ast_unreplace_sigchld(void) ast_mutex_unlock(&safe_system_lock); } -int ast_safe_system(const char *s) +/*! \brief fork and perform other preparations for spawning applications */ +static pid_t safe_exec_prep(int dualfork) { pid_t pid; - int res; - int status; #if defined(HAVE_WORKING_FORK) || defined(HAVE_WORKING_VFORK) ast_replace_sigchld(); @@ -1240,35 +1239,101 @@ int ast_safe_system(const char *s) cap_free(cap); #endif #ifdef HAVE_WORKING_FORK - if (ast_opt_high_priority) + if (ast_opt_high_priority) { ast_set_priority(0); + } /* Close file descriptors and launch system command */ ast_close_fds_above_n(STDERR_FILENO); #endif - execl("/bin/sh", "/bin/sh", "-c", s, (char *) NULL); - _exit(1); - } else if (pid > 0) { + if (dualfork) { +#ifdef HAVE_WORKING_FORK + pid = fork(); +#else + pid = vfork(); +#endif + if (pid < 0) { + /* Second fork failed. */ + /* No logger available. */ + _exit(1); + } + + if (pid > 0) { + /* This is the first fork, exit so the reaper finishes right away. */ + _exit(0); + } + + /* This is the second fork. The first fork will exit immediately so + * Asterisk doesn't have to wait for completion. + * ast_safe_system("cmd &") would run in the background, but the '&' + * cannot be added with ast_safe_execvp, so we have to double fork. + */ + } + } + + if (pid < 0) { + ast_log(LOG_WARNING, "Fork failed: %s\n", strerror(errno)); + } +#else + ast_log(LOG_WARNING, "Fork failed: %s\n", strerror(ENOTSUP)); + pid = -1; +#endif + + return pid; +} + +/*! \brief wait for spawned application to complete and unreplace sigchld */ +static int safe_exec_wait(pid_t pid) +{ + int res = -1; + +#if defined(HAVE_WORKING_FORK) || defined(HAVE_WORKING_VFORK) + if (pid > 0) { for (;;) { + int status; + res = waitpid(pid, &status, 0); if (res > -1) { res = WIFEXITED(status) ? WEXITSTATUS(status) : -1; break; - } else if (errno != EINTR) + } + if (errno != EINTR) { break; + } } - } else { - ast_log(LOG_WARNING, "Fork failed: %s\n", strerror(errno)); - res = -1; } ast_unreplace_sigchld(); -#else /* !defined(HAVE_WORKING_FORK) && !defined(HAVE_WORKING_VFORK) */ - res = -1; #endif return res; } +int ast_safe_execvp(int dualfork, const char *file, char *const argv[]) +{ + pid_t pid = safe_exec_prep(dualfork); + + if (pid == 0) { + execvp(file, argv); + _exit(1); + /* noreturn from _exit */ + } + + return safe_exec_wait(pid); +} + +int ast_safe_system(const char *s) +{ + pid_t pid = safe_exec_prep(0); + + if (pid == 0) { + execl("/bin/sh", "/bin/sh", "-c", s, (char *) NULL); + _exit(1); + /* noreturn from _exit */ + } + + return safe_exec_wait(pid); +} + /*! * \brief enable or disable a logging level to a specified console */ diff --git a/res/res_monitor.c b/res/res_monitor.c index d5e2bf2ca1..8bddf0262d 100644 --- a/res/res_monitor.c +++ b/res/res_monitor.c @@ -61,17 +61,17 @@ ASTERISK_REGISTER_FILE() - optional, if not set, defaults to wav + Optional. If not set, defaults to wav - if set, changes the filename used to the one specified. + If set, changes the filename used to the one specified.