CVE-2020-15955 Vulnerability Analysis & Exploit Details

CVE-2020-15955 Vulnerability Summary

CVE-2020-15955: In s/qmail through 4.0.07, an active MitM can inject arbitrary plaintext commands into a STARTTLS encrypted session between an SMTP client and s/qmail. This allows e-mail messages and user credentials to be sent to the MitM attacker.

Exploit Prediction Scoring System (EPSS)

The EPSS score estimates the probability that this vulnerability will be exploited in the near future.

EPSS Score: 0.13% (probability of exploit)

EPSS Percentile: 49.45% (lower percentile = lower relative risk)
This vulnerability is less risky than approximately 50.55% of others.

CVE-2020-15955 References

External References

• https://nostarttls.secvuln.info/
• https://www.fehcom.de/sqmail/sqmail.html

CWE Common Weakness Enumeration

CAPEC Common Attack Pattern Enumeration and Classification

• LDAP Injection CAPEC-136 An attacker manipulates or crafts an LDAP query for the purpose of undermining the security of the target. Some applications use user input to create LDAP queries that are processed by an LDAP server. For example, a user might provide their username during authentication and the username might be inserted in an LDAP query during the authentication process. An attacker could use this input to inject additional commands into an LDAP query that could disclose sensitive information. For example, entering a * in the aforementioned query might return information about all users on the system. This attack is very similar to an SQL injection attack in that it manipulates a query to gather additional information or coerce a particular return value.
• Command Delimiters CAPEC-15 An attack of this type exploits a programs' vulnerabilities that allows an attacker's commands to be concatenated onto a legitimate command with the intent of targeting other resources such as the file system or database. The system that uses a filter or denylist input validation, as opposed to allowlist validation is vulnerable to an attacker who predicts delimiters (or combinations of delimiters) not present in the filter or denylist. As with other injection attacks, the attacker uses the command delimiter payload as an entry point to tunnel through the application and activate additional attacks through SQL queries, shell commands, network scanning, and so on.
• IMAP/SMTP Command Injection CAPEC-183 An adversary exploits weaknesses in input validation on web-mail servers to execute commands on the IMAP/SMTP server. Web-mail servers often sit between the Internet and the IMAP or SMTP mail server. User requests are received by the web-mail servers which then query the back-end mail server for the requested information and return this response to the user. In an IMAP/SMTP command injection attack, mail-server commands are embedded in parts of the request sent to the web-mail server. If the web-mail server fails to adequately sanitize these requests, these commands are then sent to the back-end mail server when it is queried by the web-mail server, where the commands are then executed. This attack can be especially dangerous since administrators may assume that the back-end server is protected against direct Internet access and therefore may not secure it adequately against the execution of malicious commands.
• Command Injection CAPEC-248 An adversary looking to execute a command of their choosing, injects new items into an existing command thus modifying interpretation away from what was intended. Commands in this context are often standalone strings that are interpreted by a downstream component and cause specific responses. This type of attack is possible when untrusted values are used to build these command strings. Weaknesses in input validation or command construction can enable the attack and lead to successful exploitation.
• Manipulating Writeable Terminal Devices CAPEC-40 This attack exploits terminal devices that allow themselves to be written to by other users. The attacker sends command strings to the target terminal device hoping that the target user will hit enter and thereby execute the malicious command with their privileges. The attacker can send the results (such as copying /etc/passwd) to a known directory and collect once the attack has succeeded.
• Exploiting Multiple Input Interpretation Layers CAPEC-43 An attacker supplies the target software with input data that contains sequences of special characters designed to bypass input validation logic. This exploit relies on the target making multiples passes over the input data and processing a "layer" of special characters with each pass. In this manner, the attacker can disguise input that would otherwise be rejected as invalid by concealing it with layers of special/escape characters that are stripped off by subsequent processing steps. The goal is to first discover cases where the input validation layer executes before one or more parsing layers. That is, user input may go through the following logic in an application: <parser1> --> <input validator> --> <parser2>. In such cases, the attacker will need to provide input that will pass through the input validator, but after passing through parser2, will be converted into something that the input validator was supposed to stop.
• Manipulating Writeable Configuration Files CAPEC-75 Generally these are manually edited files that are not in the preview of the system administrators, any ability on the attackers' behalf to modify these files, for example in a CVS repository, gives unauthorized access directly to the application, the same as authorized users.
• Manipulating Web Input to File System Calls CAPEC-76 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.

Other 5 Recently Published CVEs Vulnerabilities

• CVE-2024-43107 – Improper Certificate Validation (CWE-295) in the Gallagher Milestone Integration Plugin (MIP) permits unauthenticated messages (e.g. alarm events) ...
• CVE-2024-41724 – Improper Certificate Validation (CWE-295) in the Gallagher Command Centre SALTO integration allowed an attacker to spoof the SALTO server. Thi...
• CVE-2025-2133 – A vulnerability classified as problematic was found in ftcms 2.1. Affected by this vulnerability is an unknown functionality of the file /admin/ind...
• CVE-2025-2132 – A vulnerability classified as critical has been found in ftcms 2.1. Affected is an unknown function of the file /admin/index.php/web/ajax_all_lists...
• CVE-2025-2131 – A vulnerability was found in dayrui XunRuiCMS up to 4.6.3. It has been rated as problematic. This issue affects some unknown processing of the comp...