CVE-2025-15366 is a command injection vulnerability classified under CWE-77, affecting the imaplib module of the Python Software Foundation's CPython implementation. The flaw occurs because the imaplib module improperly neutralizes special elements used in commands, specifically allowing user-controlled input containing newline characters to inject additional IMAP commands. This can lead to unauthorized execution of arbitrary IMAP commands within the context of an authenticated session. The vulnerability requires an attacker to have high privileges and partial authentication to the IMAP service, but does not require user interaction. The CVSS 4.0 score is 5.9 (medium severity), reflecting network attack vector, low attack complexity, partial authentication, and significant impact on confidentiality and integrity. The vulnerability does not affect availability and does not require user interaction. No known exploits have been reported in the wild as of now. The mitigation strategy involves rejecting or sanitizing commands that contain control characters such as newlines to prevent command injection. Since imaplib is widely used in Python applications for email handling, this vulnerability could affect a broad range of software relying on Python for IMAP communication, especially those processing untrusted input. The lack of a patch link suggests that a fix may be forthcoming or that users must implement input validation themselves.

For European organizations, this vulnerability poses a risk primarily to confidentiality and integrity of email communications handled via Python-based IMAP clients or services. Successful exploitation could allow attackers to execute unauthorized IMAP commands, potentially leading to unauthorized access to email data, manipulation of mailbox contents, or disruption of email workflows. Organizations in sectors such as finance, government, healthcare, and technology, which often rely on Python for backend services and email processing, may face increased risk. The requirement for partial authentication and high privileges limits exposure to some extent but does not eliminate risk, especially in environments with weak credential management or insider threats. The absence of known exploits reduces immediate risk but should not lead to complacency. Failure to mitigate could result in data breaches, regulatory non-compliance (e.g., GDPR), and reputational damage.

European organizations should implement strict input validation and sanitization for any user-controlled data passed to the imaplib module, specifically rejecting or escaping control characters such as newlines that enable command injection. Review and update Python dependencies to the latest CPython versions once patches are released. Employ network segmentation and access controls to limit IMAP service exposure and restrict high privilege accounts. Monitor IMAP logs for unusual command patterns indicative of injection attempts. Incorporate multi-factor authentication to reduce risk from compromised credentials. Conduct code audits on internal applications using imaplib to ensure secure handling of IMAP commands. Engage with Python Software Foundation updates and security advisories to apply fixes promptly. Consider deploying runtime application self-protection (RASP) or intrusion detection systems tailored to detect anomalous IMAP activity.