CVE-2018-0500 in cURL
Summary
by MITRE
Curl_smtp_escape_eob in lib/smtp.c in curl before 7.61.0 has a heap-based buffer overflow that might be exploitable by an attacker who can control the data that curl transmits over SMTP with certain settings (i.e., use of a nonstandard --limit-rate argument or CURLOPT_BUFFERSIZE value).
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Analysis
by VulDB Data Team • 04/06/2023
The vulnerability identified as CVE-2018-0500 represents a critical heap-based buffer overflow within the curl library's Simple Mail Transfer Protocol implementation. This flaw exists in the Curl_smtp_escape_eob function located in lib/smtp.c and affects curl versions prior to 7.61.0. The vulnerability stems from insufficient bounds checking when processing SMTP data transmission, specifically when handling end-of-block sequences during email transfer operations.
The technical implementation of this vulnerability occurs when curl processes SMTP communications with non-standard configuration parameters such as the --limit-rate argument or CURLOPT_BUFFERSIZE values. The heap-based buffer overflow manifests when the application fails to properly validate the size of data being written to memory buffers during SMTP escape sequence processing. This condition creates a situation where attacker-controlled data can overwrite adjacent memory locations, potentially leading to arbitrary code execution or denial of service conditions. The vulnerability falls under CWE-121 heap-based buffer overflow, which is classified as a critical weakness in memory safety.
The operational impact of CVE-2018-0500 extends beyond simple denial of service scenarios to potentially enable remote code execution within the context of the curl process. Attackers who can influence SMTP data transmission parameters or control the data being sent via SMTP can exploit this vulnerability to overwrite critical memory segments. The attack surface is particularly concerning because curl is widely used across various operating systems and applications for HTTP, FTP, and SMTP operations, making this vulnerability potentially exploitable in numerous contexts. According to ATT&CK framework category T1190, this vulnerability represents a technique for gaining initial access through network service exploitation, while the specific vector aligns with T1203 for exploitation of remote services.
Mitigation strategies for this vulnerability require immediate patching of curl installations to version 7.61.0 or later, which contains the necessary memory bounds checking fixes. Organizations should implement strict input validation for all SMTP data transmission parameters and avoid using non-standard buffer size configurations unless absolutely necessary. Network administrators should monitor SMTP traffic for anomalous patterns that might indicate exploitation attempts, while system administrators should consider implementing application whitelisting policies to restrict curl execution to trusted environments. The fix implemented in curl 7.61.0 addresses the root cause by adding proper bounds checking to the buffer allocation and data writing operations within the SMTP escape sequence processing function, thereby preventing the overflow condition from occurring.