zabbix CVE-2013-6824

Vulnerability description
-------------------------

Zabbix agent is vulnerable to remote command execution from the Zabbix server in some cases.

Please use CVE-2013-6824 to refer to this vulnerability.

This vulnerability has been reported by Recurity Labs Team.

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Details
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If a flexible (accepting parameters) user parameter is configured in the agent, including a newline in the parameters will execute newline section as a separate command even if UnsafeUserParameters are disabled.
This type of attack is only possible from Zabbix server or Zabbix proxy systems that are explicitly allowed in the agent configuration. Only flexible user parameters are vulnerable, static ones are not.

For example, a user parameter as the following would accept some prameters:

UserParameter=vfs.dir.size[*],du -s -B 1 "${1:-/tmp}" | cut -f1

The following would result in the 'id' command being executed:

echo -e "vfs.dir.size[/nid/n]" | nc localhost 10050

patch:
[php]
Index: src/libs/zbxsysinfo/sysinfo.c
===================================================================
--- src/libs/zbxsysinfo/sysinfo.c (revision 40346)
+++ src/libs/zbxsysinfo/sysinfo.c (working copy)
@@ -320,13 +320,49 @@
test_parameter(commands[i].key, PROCESS_TEST | PROCESS_USE_TEST_PARAM);
}

+static int zbx_check_user_parameter(const char *param, char *error, int max_err_len)
+{
+ const char suppressed_chars[] = "//'/"`*?[]{}~$!&;()<>|#@/n", *c;
+ char *buf = NULL;
+ int buf_alloc = 128, buf_offset = 0;
+
+ if (0 != CONFIG_UNSAFE_USER_PARAMETERS)
+ return SUCCEED;
+
+ for (c = suppressed_chars; '/0' != *c; c++)
+ {
+ if (NULL == strchr(param, *c))
+ continue;
+
+ buf = zbx_malloc(buf, buf_alloc);
+
+ for (c = suppressed_chars; '/0' != *c; c++)
+ {
+ if (c != suppressed_chars)
+ zbx_strcpy_alloc(&buf, &buf_alloc, &buf_offset, ", ");
+
+ if (0 != isprint(*c))
+ zbx_chrcpy_alloc(&buf, &buf_alloc, &buf_offset, *c);
+ else
+ zbx_snprintf_alloc(&buf, &buf_alloc, &buf_offset, 5, "0x%02x", *c);
+ }
+
+ zbx_snprintf(error, max_err_len, "special characters /"%s/" are not allowed in the parameters", buf);
+
+ zbx_free(buf);
+
+ return FAIL;
+ }
+
+ return SUCCEED;
+}
+
static int replace_param(const char *cmd, const char *param, char *out, int outlen, char *error, int max_err_len)
{
int ret = SUCCEED;
char buf[MAX_STRING_LEN];
char command[MAX_STRING_LEN];
register char *pl, *pr;
- const char suppressed_chars[] = "//'/"`*?[]{}~$!&;()<>|#@/0", *c;

assert(out);

@@ -357,23 +393,10 @@
{
get_param(param, (int)(pr[1] - '0'), buf, MAX_STRING_LEN);

- if (0 == CONFIG_UNSAFE_USER_PARAMETERS)
- {
- for (c = suppressed_chars; '/0' != *c; c++)
- if (NULL != strchr(buf, *c))
- {
- zbx_snprintf(error, max_err_len, "Special characters '%s'"
- " are not allowed in the parameters",
- suppressed_chars);
- ret = FAIL;
- break;
- }
- }
+ if (SUCCEED != (ret = zbx_check_user_parameter(buf, error, max_err_len)))
+ break;
}

- if (FAIL == ret)
- break;
-
zbx_strlcat(out, buf, outlen);
outlen -= MIN((int)strlen(buf), (int)outlen);[/php]