Exim Mail Transfer Agent (MTA) Improper Input Validation
CVE-2019-10149 is a critical-severity improper neutralization of special elements used in an OS command vulnerability in exim, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected exim versions: 4.92. The record does not name a fixed version, so check the vendor advisory. CISA added it to the Known Exploited Vulnerabilities catalogue on January 10, 2022, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Check which version of exim you run against the affected versions below, and install the vendor's latest release.
- CISA's required action: Apply updates per vendor instructions.
- Read the advisory on exim.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Exim | exim | 4.92 | Not stated |
| Canonical | Ubuntu Linux | 18.04; 18.10 | Not stated |
| Debian | Debian Linux | 9.0 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.8 | Critical | NVD |
| CVSS 3.0 | 9.0 | Critical | CNA (redhat.com) |
| CVSS 2.0 | 10.0 | High | NVD |
Official description
A flaw was found in Exim versions 4.87 to 4.91 (inclusive). Improper validation of recipient address in deliver_message() function in /src/deliver.c may lead to remote command execution.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Neutralization of Special Elements used in an OS Command
The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command before it is sent to a downstream component.
How developers prevent this class of flaw
- If at all possible, use library calls rather than external processes to recreate the desired functionality.
- For any data that will be used to generate a command to be executed, keep as much of that data out of external control as possible. For example, in web applications, this may require storing the data locally in the session's state instead of sending it out to the client in a hidden form field.
- For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
More Improper Neutralization of Special Elements used in an OS Command vulnerabilities (CWE-78)
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- openwall.com/lists/oss-security/2019/06/05/3Mailing List, Third Party Advisory
Third-party and government advisories
- lists.opensuse.org/opensuse-security-announce/2019-06/msg00020.htmlMailing List, Third Party Advisory
- seclists.org/fulldisclosure/2019/Jun/16Mailing List, Third Party Advisory
- openwall.com/lists/oss-security/2019/06/05/2Mailing List, Third Party Advisory
- openwall.com/lists/oss-security/2019/07/25/6Mailing List, Third Party Advisory
- openwall.com/lists/oss-security/2019/07/25/7Mailing List, Third Party Advisory
- openwall.com/lists/oss-security/2019/07/26/4Mailing List, Third Party Advisory
- openwall.com/lists/oss-security/2021/05/04/7Mailing List, Third Party Advisory
- bugzilla.redhat.com/show_bug.cgi?id=CVE-2019-10149Issue Tracking, Third Party Advisory
- seclists.org/bugtraq/2019/Jun/5Mailing List, Third Party Advisory
- security.gentoo.org/glsa/201906-01Third Party Advisory
- usn.ubuntu.com/4010-1/Third Party Advisory
- debian.org/security/2019/dsa-4456Third Party Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-10149US Government Resource
Technical write-ups (may include proof of concept)
- packetstormsecurity.com/files/153218/Exim-4.9.1-Remote-Command-Execution.htmlExploit, Third Party Advisory, VDB Entry
- packetstormsecurity.com/files/153312/Exim-4.91-Local-Privilege-Escalation.htmlExploit, Third Party Advisory, VDB Entry
- packetstormsecurity.com/files/154198/Exim-4.91-Local-Privilege-Escalation.htmlExploit, Third Party Advisory, VDB Entry
- openwall.com/lists/oss-security/2019/06/05/4Exploit, Mailing List
- openwall.com/lists/oss-security/2019/06/06/1Exploit, Mailing List, Third Party Advisory
Other vulnerabilities in exim
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