CVE-2025-15366 identifies a command injection vulnerability in the imaplib module of CPython, the core Python implementation maintained by the Python Software Foundation. The vulnerability arises because imaplib improperly handles user-supplied commands containing newline characters, allowing attackers to inject additional IMAP commands. This is classified under CWE-77, which concerns improper neutralization of special elements used in commands. The flaw enables an attacker with authenticated access and high privileges to manipulate the IMAP command stream by injecting newline characters that split commands, potentially executing unintended commands on the IMAP server. The vulnerability affects all versions of CPython prior to the fix, as indicated by the affectedVersions field. The CVSS 4.0 base score is 5.9 (medium severity), reflecting network attack vector, low attack complexity, partial confidentiality and integrity impact, and requiring privileges but no user interaction. No known exploits have been reported in the wild, and no official patches are linked yet. The mitigation strategy involves rejecting or sanitizing commands containing control characters, especially newlines, to prevent command injection. Given Python's extensive use in email clients, servers, and automation scripts that interact with IMAP servers, this vulnerability could be leveraged to manipulate email sessions or exfiltrate data if exploited.

The vulnerability can lead to unauthorized command execution within IMAP sessions, potentially allowing attackers to manipulate email retrieval, deletion, or mailbox state. This compromises the confidentiality and integrity of email data. Since exploitation requires authenticated access with high privileges, the risk is somewhat limited to insiders or compromised accounts. However, in environments where Python scripts or applications handle untrusted IMAP commands, the vulnerability could be exploited to escalate privileges or disrupt email services. Organizations relying on Python-based email clients, automated email processing, or server-side IMAP interactions may face data breaches, service disruptions, or unauthorized data manipulation. The lack of user interaction requirement increases the risk of automated exploitation once credentials are obtained. Although no availability impact is noted, integrity and confidentiality impacts are significant enough to warrant attention. The medium severity score reflects these factors, but the widespread use of Python and email infrastructure increases the potential attack surface globally.

1. Immediately apply any official patches or updates released by the Python Software Foundation addressing CVE-2025-15366. 2. Implement strict input validation and sanitization in all applications using imaplib, explicitly rejecting or escaping control characters such as newlines in IMAP commands. 3. Restrict IMAP access to trusted users and enforce strong authentication mechanisms to reduce the risk of credential compromise. 4. Monitor IMAP traffic for anomalous command sequences that may indicate injection attempts. 5. Employ network segmentation and least privilege principles to limit the impact of a compromised account. 6. Review and audit Python scripts and applications interacting with IMAP servers to ensure they do not pass untrusted input directly to imaplib commands. 7. Consider using alternative libraries or wrappers that have implemented robust input sanitization if immediate patching is not feasible. 8. Educate developers and administrators about the risks of command injection and secure coding practices related to IMAP command handling.