{"id":35011,"date":"2019-10-31T22:01:50","date_gmt":"2019-10-31T19:01:50","guid":{"rendered":"https:\/\/prohoster.info\/blog\/kriticheskaya-uyazvimost-v-exim-pozvolyayushhaya-vypolnit-kod-na-servere-s-pravami-root\/"},"modified":"2019-10-31T22:01:50","modified_gmt":"2019-10-31T19:01:50","slug":"kriticheskaya-uyazvimost-v-exim-pozvolyayushhaya-vypolnit-kod-na-servere-s-pravami-root","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/news\/kriticheskaya-uyazvimost-v-exim-pozvolyayushhaya-vypolnit-kod-na-servere-s-pravami-root","title":{"rendered":"A critical vulnerability in Exim allows code execution on the server with root privileges","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

In the Exim mail server identified<\/a><\/noindex> critical vulnerability<\/a><\/noindex> (CVE-2019-10149<\/a><\/noindex>), which can lead to remote code execution on the server with root privileges when processing a specifically formatted request. The vulnerability is present in versions 4.87 through 4.91 inclusive or when compiled with the EXPERIMENTAL_EVENT option.<\/p>\n

In the default configuration, an attack can be executed without complications by a local user, as the ACL 'verify = recipient' applies additional checks for external addresses. A remote attack can occur by altering settings, such as when operating as a secondary MX for another domain, removing the ACL 'verify = recipient', or making specific changes to local_part_suffix. A remote attack is also possible if an attacker can keep a connection to the server open for 7 days (for example, by sending one byte per minute to avoid timeout disconnection). Furthermore, it should not be ruled out that there are simpler vectors for remotely exploiting the issue.<\/p>\n

The vulnerability is caused by incorrect recipient address verification in the deliver_message() function, defined in the file \/src\/deliver.c. By manipulating the address formatting, an attacker can substitute their data into the arguments of a command invoked via the execv() function with root privileges. Exploitation does not require complex techniques used in buffer overflows or memory corruption; it is sufficient to simply substitute characters. <\/p>\n

The issue is related to the use of the following construct for address transformation:<\/p>\n

deliver_localpart = expand_string(
\n string_sprintf('${local_part:%s}', new->address));
\n deliver_domain = expand_string(
\n string_sprintf('${domain:%s}', new->address));<\/p>\n

The function expand_string() is an overly complex machine, including recognizing the command '${run{command arguments}', leading to the execution of an external handler. Thus, for an attack during an SMTP session, a local user only needs to send a command like 'RCPT TO '${username+${run{\u2026}}@localhost'', where localhost is one of the hosts from the local_domains list and username is the name of an existing local user. <\/p>\n

If the server operates as a mail relay, it is sufficient to remotely send the command 'RCPT TO '${run{\u2026}}@relaydomain.com'', where relaydomain.com is one of the hosts listed in the relay_to_domains settings section. Since the privilege drop mode is not applied by default in exim (deliver_drop_privilege = false), commands passed via '${run{\u2026}}' will be executed with root privileges.<\/p>\n

It is noteworthy that the vulnerability was has been closed<\/a><\/noindex> in the February release 4.92 without drawing attention to the fact that the fix could lead to security issues. There is no reason to believe that the Exim developers intentionally concealed the vulnerability, as the issue was resolved during the fix<\/a><\/noindex> for a failure occurring when transmitting incorrect addresses, and the vulnerability was identified by Qualys during an audit of changes in Exim. <\/p>\n

The fix for earlier versions, which continue to be used in distributions, is currently available only in the form of a patch<\/a><\/noindex>. Correction releases for earlier branches to address the issue are scheduled for June 11. Package updates have been prepared for Debian<\/a><\/noindex>, Ubuntu<\/a><\/noindex>, The release of SEMMi Analytics 2.0<\/a><\/noindex>. Arch Linux<\/a><\/noindex> and Alpine<\/a><\/noindex> which deliver version 4.92, in which the issue does not occur. RHEL and CentOS are not affected by the issue, as Exim is not included in their standard package repository.<\/a><\/noindex>, as Exim is not included in their standard package repository.<\/p>\n

<\/a><\/noindex><\/p>\n

Source: opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u0442\u0435\u043b\u0435\u043c, […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-35011","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47Critical vulnerability in Exim allows code execution on the server with root privileges | ProHoster","description":"A critical vulnerability has been identified in the Exim mail 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