Vulnerabilities > CVE-2020-8015 - Link Following vulnerability in Exim
Attack vector
LOCAL Attack complexity
LOW Privileges required
NONE Confidentiality impact
COMPLETE Integrity impact
COMPLETE Availability impact
COMPLETE Summary
A UNIX Symbolic Link (Symlink) Following vulnerability in the packaging of exim in openSUSE Factory allows local attackers to escalate from user mail to root. This issue affects: openSUSE Factory exim versions prior to 4.93.0.4-3.1.
Vulnerable Configurations
Common Weakness Enumeration (CWE)
Common Attack Pattern Enumeration and Classification (CAPEC)
- Symlink Attack An attacker positions a symbolic link in such a manner that the targeted user or application accesses the link's endpoint, assuming that it is accessing a file with the link's name. The endpoint file may be either output or input. If the file is output, the result is that the endpoint is modified, instead of a file at the intended location. Modifications to the endpoint file may include appending, overwriting, corrupting, changing permissions, or other modifications. In some variants of this attack the attacker may be able to control the change to a file while in other cases they cannot. The former is especially damaging since the attacker may be able to grant themselves increased privileges or insert false information, but the latter can also be damaging as it can expose sensitive information or corrupt or destroy vital system or application files. Alternatively, the endpoint file may serve as input to the targeted application. This can be used to feed malformed input into the target or to cause the target to process different information, possibly allowing the attacker to control the actions of the target or to cause the target to expose information to the attacker. Moreover, the actions taken on the endpoint file are undertaken with the permissions of the targeted user or application, which may exceed the permissions that the attacker would normally have.
- Accessing, Modifying or Executing Executable Files An attack of this type exploits a system's configuration that allows an attacker to either directly access an executable file, for example through shell access; or in a possible worst case allows an attacker to upload a file and then execute it. Web servers, ftp servers, and message oriented middleware systems which have many integration points are particularly vulnerable, because both the programmers and the administrators must be in synch regarding the interfaces and the correct privileges for each interface.
- Leverage Executable Code in Non-Executable Files An attack of this type exploits a system's trust in configuration and resource files, when the executable loads the resource (such as an image file or configuration file) the attacker has modified the file to either execute malicious code directly or manipulate the target process (e.g. application server) to execute based on the malicious configuration parameters. Since systems are increasingly interrelated mashing up resources from local and remote sources the possibility of this attack occurring is high. The attack can be directed at a client system, such as causing buffer overrun through loading seemingly benign image files, as in Microsoft Security Bulletin MS04-028 where specially crafted JPEG files could cause a buffer overrun once loaded into the browser. Another example targets clients reading pdf files. In this case the attacker simply appends javascript to the end of a legitimate url for a pdf (http://www.gnucitizen.org/blog/danger-danger-danger/) http://path/to/pdf/file.pdf#whatever_name_you_want=javascript:your_code_here The client assumes that they are reading a pdf, but the attacker has modified the resource and loaded executable javascript into the client's browser process. The attack can also target server processes. The attacker edits the resource or configuration file, for example a web.xml file used to configure security permissions for a J2EE app server, adding role name "public" grants all users with the public role the ability to use the administration functionality. The server trusts its configuration file to be correct, but when they are manipulated, the attacker gains full control.
- Manipulating Input to File System Calls An attacker manipulates inputs to the target software which the target software passes to file system calls in the OS. The goal is to gain access to, and perhaps modify, areas of the file system that the target software did not intend to be accessible.
Nessus
NASL family SMTP problems NASL id EXIM_4_93.NASL description According to its banner, the version of Exim running on the remote host is prior to 4.93. It is, therefore, potentially affected by a privilege escalation vulnerability. A flaw exists in the UNIX symbolic link that could allow an attacker to execute to escalate from the mail user to root. last seen 2020-04-14 modified 2020-04-10 plugin id 135311 published 2020-04-10 reporter This script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof. source https://www.tenable.com/plugins/nessus/135311 title Exim < 4.93 Privilege Escalation vulnerability code # # (C) Tenable Network Security, Inc. # include('compat.inc'); if (description) { script_id(135311); script_version("1.3"); script_set_attribute(attribute:"plugin_modification_date", value:"2020/04/13"); script_cve_id("CVE-2020-8015"); script_xref(name:"IAVA", value:"2020-A-0131"); script_name(english:"Exim < 4.93 Privilege Escalation vulnerability"); script_summary(english:"Checks the version of the SMTP banner."); script_set_attribute(attribute:"synopsis", value: "The remote mail server is potentially affected by a privilege escalation vulnerability."); script_set_attribute(attribute:"description", value: "According to its banner, the version of Exim running on the remote host is prior to 4.93. It is, therefore, potentially affected by a privilege escalation vulnerability. A flaw exists in the UNIX symbolic link that could allow an attacker to execute to escalate from the mail user to root."); # https://bugzilla.suse.com/show_bug.cgi?id=1154183 script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?f294b9cf"); # https://access.redhat.com/security/cve/cve-2020-8015 script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?cc28c77b"); # https://vulmon.com/vulnerabilitydetails?qid=CVE-2020-8015 script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?728dbb7f"); script_set_attribute(attribute:"solution", value: "Upgrade to Exim 4.93 or later."); script_set_cvss_base_vector("CVSS2#AV:L/AC:L/Au:N/C:C/I:C/A:C"); script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C"); script_set_cvss3_base_vector("CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"); script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C"); script_set_attribute(attribute:"cvss_score_source", value:"CVE-2020-8015"); script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available"); script_set_attribute(attribute:"vuln_publication_date", value:"2020/04/01"); script_set_attribute(attribute:"patch_publication_date", value:"2020/04/10"); script_set_attribute(attribute:"plugin_publication_date", value:"2020/04/10"); script_set_attribute(attribute:"potential_vulnerability", value:"true"); script_set_attribute(attribute:"plugin_type", value:"remote"); script_set_attribute(attribute:"cpe", value:"cpe:/a:exim:exim"); script_set_attribute(attribute:"stig_severity", value:"I"); script_end_attributes(); script_category(ACT_GATHER_INFO); script_family(english:"SMTP problems"); script_copyright(english:"This script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof."); script_dependencies("smtpserver_detect.nasl"); script_require_keys("Settings/ParanoidReport"); script_require_ports("Services/smtp", 25); exit(0); } include("audit.inc"); include("global_settings.inc"); include("misc_func.inc"); include("smtp_func.inc"); if (report_paranoia < 2) audit(AUDIT_PARANOID); port = get_service(svc:"smtp", default:25, exit_on_fail:TRUE); banner = get_smtp_banner(port:port); if (!banner) audit(AUDIT_NO_BANNER, port); if ("Exim" >!< banner) audit(AUDIT_NOT_LISTEN, 'Exim', port); matches = pregmatch(pattern:"220.*Exim ([0-9\._]+)", string:banner); if (isnull(matches)) audit(AUDIT_SERVICE_VER_FAIL, 'Exim', port); version = matches[1]; # Underscore was added to the vesion version = ereg_replace(string:version, pattern:'_', replace:'.'); if (ver_compare(ver:version, fix:'4.93', strict:FALSE) < 0) { report = '\n Banner : ' + banner + '\n Installed version : ' + version + '\n Fixed version : 4.93'; security_report_v4(port:port, severity:SECURITY_HOLE, extra:report); } else audit(AUDIT_LISTEN_NOT_VULN, 'Exim', port, version);NASL family SuSE Local Security Checks NASL id OPENSUSE-2020-491.NASL description This update for exim fixes the following issues : - CVE-2020-8015: Fixed a local privilege escalation from user mail to root (boo#1154183). last seen 2020-04-16 modified 2020-04-10 plugin id 135386 published 2020-04-10 reporter This script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof. source https://www.tenable.com/plugins/nessus/135386 title openSUSE Security Update : exim (openSUSE-2020-491)