CVE-2020-12063
Description
For some of the Postfix configurations, the remote user can send e-mails pretending to be someone else (or even using non-existing user name with some homoglyph characters). One of the discussed problems that Postfix params "smtpd_sender_login_maps" and "smtpd_sender_restrictions" looks useless because works only for authorized users and attacker could get round with anonymous sending e-mails to any local user. The described issue should not be considered as security issue, so it is "DISPUTED".
Statement
Red Hat Product Security does not consider this to be a vulnerability. The described problem is problem of possibly incorrect Postfix configuration, but not bug of Postfix itself. Both no way to totally resolve the described in CVE problem, because it is how SMTP protocol designed. Means that SMTP protocol allows some SPAM or forging e-mails and no way to prevent it totally, but if configuring Postfix well, then possible to make it more strict (less SPAM and less forging).
Mitigation
The described problem could be prevented with the usage of the postfix configuration param check_sender_access (part of smtpd_sender_restrictions) for domain names being used for receiving e-mails with param reject_unverified_sender for each of these domains.
The related part of postfix configuration example:
smtpd_sender_login_maps = texthash:/etc/postfix/sender_login
smtpd_sender_restrictions =
check_sender_access texthash:/etc/postfix/sender_access
reject_sender_login_mismatch
reject_unknown_sender_domain
and the content of the file /etc/postfix/sender_access would be:
mail.mydomain.com reject_unverified_sender
and the content of the file /etc/postfix/sender_login would be:
username@mail.mydomain.com username@mail.mydomain.com
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 0 | 5.3 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | Low | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Red Hat CVSS v3 Score Explanation
No security impact. Instead describes some of the Postfix configuration features.
Understanding the Weakness (CWE)
Integrity,Other
Technical Impact: Varies by Context; Unexpected State
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