CVE-2017-1000100 in macOS
Summary
by MITRE
When doing a TFTP transfer and curl/libcurl is given a URL that contains a very long file name (longer than about 515 bytes), the file name is truncated to fit within the buffer boundaries, but the buffer size is still wrongly updated to use the untruncated length. This too large value is then used in the sendto() call, making curl attempt to send more data than what is actually put into the buffer. The endto() function will then read beyond the end of the heap based buffer. A malicious HTTP(S) server could redirect a vulnerable libcurl-using client to a crafted TFTP URL (if the client hasn't restricted which protocols it allows redirects to) and trick it to send private memory contents to a remote server over UDP. Limit curl's redirect protocols with --proto-redir and libcurl's with CURLOPT_REDIR_PROTOCOLS.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 01/21/2021
The vulnerability identified as CVE-2017-1000100 represents a critical buffer overflow condition within the libcurl library that manifests during TFTP (Trivial File Transfer Protocol) operations. This flaw exists in the way curl handles file names that exceed approximately 515 bytes in length when processing TFTP URLs. The underlying issue stems from improper buffer management where the system correctly truncates the excessively long file name to fit within predetermined buffer boundaries but fails to update the associated buffer size metadata accordingly. This discrepancy creates a scenario where the application maintains an incorrect buffer size indicator while the actual data remains truncated, leading to a fundamental mismatch between expected and actual memory boundaries.
The technical exploitation of this vulnerability occurs through a carefully crafted TFTP URL that leverages the buffer overflow condition to cause memory corruption. When curl processes such a URL, the incorrect buffer size value is subsequently passed to the sendto() system call, which attempts to transmit more data than what was actually stored in the allocated buffer space. This fundamental mismatch results in the sendto() function reading beyond the legitimate heap-based buffer boundaries, potentially accessing and transmitting arbitrary memory contents from the process's heap. The vulnerability is particularly dangerous because it can be triggered remotely through HTTP(S) server redirection, where a malicious server can redirect a vulnerable curl client to a specially crafted TFTP URL without requiring any user interaction beyond the initial request.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable information disclosure attacks that could expose sensitive data from the victim's memory space. Attackers can exploit this weakness by crafting malicious HTTP(S) responses that redirect vulnerable clients to malicious TFTP servers, allowing them to harvest private memory contents such as authentication tokens, session data, or other sensitive information. The vulnerability affects any application that uses the vulnerable version of libcurl and has not implemented proper protocol restriction measures. This makes it particularly concerning for web applications, automated systems, and network clients that may follow redirects without proper protocol validation, as these systems could unknowingly become vectors for information leakage.
Security mitigations for CVE-2017-1000100 primarily focus on two key approaches that align with established security best practices. The first and most effective mitigation involves restricting protocol redirection behavior through the use of curl's --proto-redir command-line option or libcurl's CURLOPT_REDIR_PROTOCOLS function, which prevents automatic redirection to potentially dangerous protocols like TFTP. This approach directly addresses the attack vector by eliminating the possibility of malicious servers redirecting vulnerable clients to TFTP URLs. Additionally, users should upgrade to patched versions of libcurl where the buffer management logic has been corrected to properly synchronize buffer size metadata with actual data content, ensuring that buffer overflow conditions cannot occur due to size mismatches. This vulnerability aligns with CWE-121 and CWE-122 categories related to buffer overflow conditions, and the attack pattern corresponds to techniques found in the ATT&CK framework under T1059 for command and scripting interpreter and T1566 for credential access through network protocols.