CVE-2010-3493 in Python
Summary
by MITRE
Multiple race conditions in smtpd.py in the smtpd module in Python 2.6, 2.7, 3.1, and 3.2 alpha allow remote attackers to cause a denial of service (daemon outage) by establishing and then immediately closing a TCP connection, leading to the accept function having an unexpected return value of None, an unexpected value of None for the address, or an ECONNABORTED, EAGAIN, or EWOULDBLOCK error, or the getpeername function having an ENOTCONN error, a related issue to CVE-2010-3492.
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Analysis
by VulDB Data Team • 09/27/2021
The vulnerability described in CVE-2010-3493 represents a critical race condition flaw within Python's smtpd module that affects versions 2.6, 2.7, 3.1, and 3.2 alpha releases. This issue specifically targets the smtpd.py implementation which serves as an SMTP server daemon functionality within Python's standard library. The vulnerability arises from improper handling of concurrent TCP connection operations within the socket accept and getpeername functions, creating exploitable conditions that can be leveraged by remote attackers to disrupt service availability.
The technical flaw manifests through multiple race conditions that occur during the TCP connection handling process within the smtpd module. When a remote attacker establishes a TCP connection and immediately closes it, the underlying accept function can return unexpected values including None instead of a valid socket object, or the address parameter may contain None values rather than the expected connection details. Additionally, the system may encounter ECONNABORTED, EAGAIN, or EWOULDBLOCK error conditions that are not properly handled, while the getpeername function can trigger ENOTCONN errors when attempting to retrieve peer connection information. These race conditions create a cascade of failure states that can lead to daemon instability and complete service outage.
The operational impact of this vulnerability extends beyond simple denial of service to potentially compromise the entire SMTP daemon functionality that relies on Python's smtpd module. Attackers can exploit this weakness by repeatedly establishing and closing connections in rapid succession, causing the daemon to enter an inconsistent state where it cannot properly handle legitimate incoming connections. This creates a persistent availability issue that affects email services, mail servers, and any applications that depend on Python's built-in SMTP server capabilities. The vulnerability particularly affects systems running Python-based mail servers where the smtpd module is actively used to process incoming email traffic.
Mitigation strategies for CVE-2010-3493 require immediate patching of affected Python versions to address the race condition vulnerabilities in the smtpd module. Organizations should prioritize upgrading to patched versions of Python 2.6, 2.7, 3.1, and 3.2 where the race conditions have been properly resolved. Network-level protections such as connection rate limiting and implementing proper firewall rules can help reduce the impact of exploitation attempts while awaiting patches. Security monitoring should include detection of unusual connection patterns and rapid connection establishment and termination that may indicate exploitation attempts. This vulnerability aligns with CWE-362, which catalogs race conditions as a fundamental security weakness, and represents a specific implementation issue that falls under the ATT&CK technique of denial of service through resource exhaustion and daemon instability. Organizations should also consider implementing intrusion detection systems that can identify patterns consistent with this specific exploitation method and maintain comprehensive backup and recovery procedures for critical mail services that rely on affected Python versions.