Source: cve@mitre.org
MIME buffer overflow in email clients, e.g. Solaris mailtool and Outlook.
Critical vulnerability discovered in 1997, CVE-1999-0004, allows for remote code execution via a buffer overflow in email clients. Successful exploitation grants attackers complete control over the compromised system, potentially leading to data breaches and system compromise.
Step 1: Payload Creation: An attacker crafts a malicious email message. This email contains a MIME-encoded section with a specially crafted header or content. The malicious content is designed to be larger than the buffer allocated by the vulnerable email client.
Step 2: Email Delivery: The attacker sends the crafted email to a target user. The email is delivered to the target's email server and subsequently retrieved by the vulnerable email client.
Step 3: Email Parsing: The vulnerable email client parses the received email, including the MIME-encoded section. The client attempts to decode and store the MIME data in a buffer.
Step 4: Buffer Overflow: Due to the oversized malicious content, the buffer overflows. The overflowing data overwrites adjacent memory locations, including the stack.
Step 5: Code Execution: The overwritten memory locations contain critical program data, including the return address. The attacker's crafted payload overwrites the return address with the address of their injected malicious code. When the function returns, control is transferred to the attacker's code.
Step 6: System Compromise: The attacker's code executes, granting them control over the compromised system. This can include installing malware, stealing data, or gaining further access to the network.
The vulnerability stems from a buffer overflow in how email clients, such as Solaris mailtool and early versions of Outlook, handle MIME (Multipurpose Internet Mail Extensions) encoded data. Specifically, the flaw lies in the parsing and processing of MIME headers and content. When a malicious email containing an overly long MIME header or content section is received, the email client attempts to store this data in a fixed-size buffer. Due to inadequate bounds checking, the oversized data overwrites adjacent memory locations, including the stack, potentially overwriting critical program data or control flow instructions. This allows an attacker to inject and execute arbitrary code, achieving remote code execution.
While specific APT groups are not directly linked to this CVE, the nature of the vulnerability makes it attractive to various threat actors. The potential for remote code execution allows for a wide range of malicious activities, including initial access for ransomware or data theft. The age of the vulnerability means it's more likely to be used in opportunistic attacks or targeted attacks against legacy systems. This CVE is not listed in the CISA KEV at this time.
Network Intrusion Detection Systems (IDS) can be configured to detect suspicious MIME headers or content lengths exceeding expected values.
Email security gateways can be configured to filter out emails with excessively long MIME headers or content sections.
Endpoint Detection and Response (EDR) solutions can monitor for suspicious process behavior, such as the execution of shellcode or the creation of unexpected files after an email is opened.
Forensic analysis of email client logs can reveal the receipt of malicious emails and the subsequent actions taken by the client.
Memory analysis of email client processes can reveal evidence of buffer overflows and injected code.
Ensure all email clients are updated to the latest versions. This is the primary and most effective mitigation strategy.
Implement a robust email security gateway to scan incoming emails for malicious content, including oversized MIME headers and content sections.
Employ a defense-in-depth strategy, including network segmentation, intrusion detection systems, and endpoint security solutions.
Regularly audit and patch all systems, especially those running legacy software.
Educate users about the risks of opening suspicious emails and attachments.