CVE-2018-14618 in cURL
Summary
by MITRE
curl before version 7.61.1 is vulnerable to a buffer overrun in the NTLM authentication code. The internal function Curl_ntlm_core_mk_nt_hash multiplies the length of the password by two (SUM) to figure out how large temporary storage area to allocate from the heap. The length value is then subsequently used to iterate over the password and generate output into the allocated storage buffer. On systems with a 32 bit size_t, the math to calculate SUM triggers an integer overflow when the password length exceeds 2GB (2^31 bytes). This integer overflow usually causes a very small buffer to actually get allocated instead of the intended very huge one, making the use of that buffer end up in a heap buffer overflow. (This bug is almost identical to CVE-2017-8816.)
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Analysis
by VulDB Data Team • 05/07/2023
The vulnerability described in CVE-2018-14618 represents a critical buffer overflow flaw within the curl library's NTLM authentication implementation. This issue affects curl versions prior to 7.61.1 and stems from improper handling of password length calculations during the NTLM authentication process. The flaw specifically resides in the internal function Curl_ntlm_core_mk_nt_hash which is responsible for generating NT hash values for authentication purposes. When processing passwords exceeding 2GB in length, the function performs arithmetic operations that trigger integer overflow conditions, fundamentally compromising the memory allocation process.
The technical mechanism of this vulnerability operates through a multiplication operation that calculates the required buffer size by doubling the password length value. This calculation is performed using a 32-bit size_t data type which has inherent limitations in representing very large values. When the password length surpasses the 2^31 byte threshold, the mathematical operation causes an integer overflow that results in a dramatically reduced buffer allocation. Instead of allocating the intended massive buffer for the cryptographic hash computation, the system allocates only a minimal buffer size that is insufficient for the actual data processing. This mismatch between allocated memory and required processing space creates a classic heap buffer overflow condition where subsequent writes to the buffer exceed its boundaries.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to potentially enable arbitrary code execution within applications that utilize curl for network communications. Attackers can exploit this flaw by crafting specially formatted authentication requests with extremely long passwords that trigger the integer overflow condition. The vulnerability is particularly concerning because it affects a widely used network transfer library that is integral to countless applications, from web browsers to enterprise software solutions. The similarity to CVE-2017-8816 demonstrates a recurring pattern in curl's authentication handling code that requires careful attention to integer overflow protections in memory management operations.
This vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions that can lead to buffer overflows and memory corruption. The flaw also maps to ATT&CK technique T1071.004, which covers application layer protocol usage in network communication. The security implications are particularly severe because NTLM authentication is commonly used in enterprise environments for single sign-on systems and internal network authentication. Organizations running affected curl versions are vulnerable to remote exploitation, as the buffer overflow can be triggered through network-based authentication attempts without requiring local system access. The vulnerability demonstrates the critical importance of proper integer overflow protection in cryptographic libraries and authentication systems, where memory management errors can have cascading security consequences.
The recommended mitigation strategy involves upgrading to curl version 7.61.1 or later, which includes fixed implementations that properly handle large password lengths through improved integer overflow protection mechanisms. Security administrators should also consider implementing network segmentation and authentication protocol restrictions to limit exposure while applying patches. Additionally, monitoring network traffic for unusual authentication patterns and implementing intrusion detection systems can help identify potential exploitation attempts. The vulnerability serves as a reminder of the critical need for thorough security testing of memory management functions, particularly in cryptographic and authentication code paths where integer overflows can lead to severe memory corruption vulnerabilities.