CVE-2000-0319 in Sendmail
Summary
by MITRE
mail.local in Sendmail 8.10.x does not properly identify the .\n string which identifies the end of message text, which allows a remote attacker to cause a denial of service or corrupt mailboxes via a message line that is 2047 characters long and ends in .\n.
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Analysis
by VulDB Data Team • 10/16/2025
The vulnerability identified as CVE-2000-0319 represents a critical buffer handling flaw within the mail.local component of Sendmail version 8.10.x series. This issue stems from improper parsing of message boundaries where the system fails to correctly identify the terminating sequence that denotes the end of message text. The flaw specifically manifests when processing email messages containing lines that are exactly 2047 characters long and conclude with a period character. This particular string sequence triggers a condition where the mail processing daemon becomes unable to properly terminate message parsing, creating a scenario that can lead to either complete service disruption or mailbox corruption.
The technical root cause of this vulnerability aligns with CWE-122, which describes buffer overflow conditions where insufficient bounds checking allows for improper memory manipulation. In this case, the mail.local component employs a flawed parsing algorithm that does not adequately validate message line terminators, particularly when encountering the specific 2047-character line ending with a period. The vulnerability operates at the protocol level where email message boundaries are not properly handled, creating a condition that can be exploited by remote attackers without requiring authentication or special privileges. This type of flaw represents a classic example of improper input validation where the system assumes standard message formatting without accounting for edge cases that could trigger memory corruption or parsing errors.
The operational impact of this vulnerability extends beyond simple denial of service to include potential mailbox corruption that could result in data loss or message integrity issues. When an attacker crafts a malicious email message with the specific 2047-character line ending in a period, the mail.local daemon processes this input and fails to properly terminate the message parsing sequence. This condition can cause the daemon to either enter an infinite loop, consume excessive system resources, or corrupt internal data structures that maintain mailbox state information. The vulnerability affects the core mail processing functionality and can potentially impact multiple users if the mail server processes the malicious message through standard mail queue processing mechanisms. The attack vector is particularly dangerous because it requires minimal input complexity and can be executed remotely, making it an attractive target for automated exploitation tools.
Mitigation strategies for this vulnerability involve immediate patching of Sendmail installations to versions that properly handle message boundary conditions and implement proper input validation for message line terminators. System administrators should also consider implementing message filtering rules that can detect and reject messages containing lines of exactly 2047 characters, particularly when such lines end with period characters. Network-level firewalls can be configured to block suspicious message patterns, though this approach may impact legitimate email traffic. The vulnerability demonstrates the importance of robust input validation and boundary checking in mail processing systems, and aligns with ATT&CK technique T1499.004 which covers network denial of service attacks. Organizations should also implement monitoring and alerting for unusual mail processing behavior that could indicate exploitation attempts, as the vulnerability can be used to create persistent service disruption conditions that may go unnoticed for extended periods.