CVE-2017-1000099 in cURL
Summary
by MITRE
When asking to get a file from a file:// URL, libcurl provides a feature that outputs meta-data about the file using HTTP-like headers. The code doing this would send the wrong buffer to the user (stdout or the application's provide callback), which could lead to other private data from the heap to get inadvertently displayed. The wrong buffer was an uninitialized memory area allocated on the heap and if it turned out to not contain any zero byte, it would continue and display the data following that buffer in memory.
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Analysis
by VulDB Data Team • 01/09/2021
The vulnerability identified as CVE-2017-1000099 resides within the libcurl library's handling of file:// URLs, specifically when retrieving file metadata through HTTP-like headers. This flaw represents a classic heap-based information disclosure vulnerability that exploits improper buffer management during file metadata retrieval operations. The vulnerability stems from libcurl's implementation of the FILE protocol handler which allows applications to fetch file information via URL schemes, creating a potential attack surface where sensitive data might be inadvertently exposed.
The technical flaw manifests in the improper handling of memory buffers when processing file metadata responses. When libcurl encounters a file:// URL request, it attempts to provide metadata information using HTTP-like headers, but the implementation contains a critical error in buffer management. The code incorrectly directs output to either stdout or an application-provided callback function, but the buffer being sent contains uninitialized memory from the heap. This uninitialized memory area, allocated on the heap, may contain remnants of previous operations or sensitive data that was previously stored in that memory location.
The operational impact of this vulnerability extends beyond simple information disclosure, as it can potentially expose private data from the heap memory space. The vulnerability's behavior depends on the contents of the uninitialized memory buffer, specifically whether it contains zero bytes to terminate the data display. When the buffer does not contain a zero byte, the memory display continues beyond the intended buffer boundaries, potentially revealing sensitive information from adjacent memory locations. This could include remnants of passwords, cryptographic keys, session tokens, or other confidential data that was previously stored in the heap memory.
This vulnerability aligns with CWE-125: Out-of-bounds Read, which describes situations where applications read data past the boundaries of allocated buffers. The flaw also connects to ATT&CK technique T1005: Data from Local System, as it enables adversaries to extract sensitive information from the target system through memory disclosure mechanisms. The issue represents a memory safety vulnerability that could be exploited by attackers who control the file system or have the ability to influence the heap memory layout, potentially leading to more severe consequences including credential theft or privilege escalation.
Mitigation strategies for CVE-2017-1000099 involve updating to libcurl versions that have patched the buffer management issue, specifically libcurl version 7.54.1 and later. Organizations should also implement proper input validation for file:// URL handling and consider disabling file protocol support in applications that do not require it. Additional defensive measures include monitoring for unusual memory access patterns and implementing memory sanitization techniques to prevent uninitialized memory from containing sensitive data. The patch addresses the core issue by ensuring that the correct buffer is used for output operations and by properly initializing memory areas before use.