CVE-2025-11468 is a vulnerability identified in the Python Software Foundation's CPython implementation, specifically affecting versions 0 through 3.15.0a1. The issue arises during the folding of long comments in email headers when those comments contain exclusively unfoldable characters. In such cases, the folding process fails to preserve parentheses, which are critical for maintaining the structural integrity of the email header. This improper handling can be exploited to inject additional headers into email messages if the email addresses involved are user-controlled and not properly sanitized. The vulnerability is particularly relevant in contexts where Python scripts or applications parse, generate, or manipulate email headers, such as automated mailing systems or email clients built on CPython. The CVSS 4.0 base score is 5.7, indicating a medium severity level. The vector indicates network attack vector (AV:N), low attack complexity (AC:L), but requires privileges (PR:H) and user interaction (UI:P). The vulnerability impacts the integrity and confidentiality of email communications by enabling header injection, which can facilitate spoofing, phishing, or bypassing email security controls. No known exploits have been reported in the wild as of the publication date. The vulnerability was reserved in October 2025 and published in January 2026, with no patch links currently provided, suggesting that fixes may be forthcoming or in development.

For European organizations, this vulnerability poses a moderate risk primarily to those relying on CPython for email processing, automation, or client applications. Successful exploitation could allow attackers to inject malicious headers into emails, potentially enabling phishing campaigns, spoofing of sender addresses, or evasion of spam filters. This could undermine trust in email communications, lead to data leakage, or facilitate further social engineering attacks. Sectors such as finance, government, healthcare, and critical infrastructure, which heavily depend on secure email communications, are particularly at risk. The requirement for high privileges and user interaction reduces the likelihood of widespread automated exploitation but does not eliminate targeted attacks. Organizations with inadequate input sanitization in email-related Python code are especially vulnerable. The impact on confidentiality and integrity is significant, while availability impact is minimal. Given the widespread use of Python across Europe, the vulnerability could affect a broad range of applications and services.

Organizations should proactively monitor for updates from the Python Software Foundation and apply patches promptly once available. Until patches are released, developers should audit and sanitize all user-controlled inputs used in email headers to prevent injection of malicious content. Employ strict validation and escaping of email addresses and header fields in Python applications. Consider implementing additional email security controls such as SPF, DKIM, and DMARC to detect and mitigate spoofed emails. Use email libraries or frameworks that have been verified to handle header folding securely. Conduct code reviews and penetration testing focused on email handling components. Limit privileges of processes handling email generation to reduce exploitation impact. Educate developers and security teams about this specific vulnerability to ensure awareness and readiness.