CVE-2017-16879 in ncurses
Summary
by MITRE
Stack-based buffer overflow in the _nc_write_entry function in tinfo/write_entry.c in ncurses 6.0 allows attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted terminfo file, as demonstrated by tic.
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Analysis
by VulDB Data Team • 01/11/2023
The vulnerability identified as CVE-2017-16879 represents a critical stack-based buffer overflow within the ncurses library version 6.0, specifically within the _nc_write_entry function located in tinfo/write_entry.c. This flaw exists in the terminal information database handling mechanism that ncurses employs to manage terminal capabilities and characteristics. The vulnerability manifests when the tic utility processes maliciously crafted terminfo files, which are used to compile terminal descriptions into binary format for efficient runtime access. The stack buffer overflow occurs during the parsing and writing operations of terminal entries, creating a potential pathway for remote code execution or system compromise.
The technical implementation of this vulnerability stems from inadequate bounds checking within the _nc_write_entry function where input data from terminfo files is processed without sufficient validation of buffer boundaries. When tic encounters a specially crafted terminfo file containing oversized or malformed data sequences, the function fails to properly validate the size of incoming data against allocated stack buffer space. This allows attackers to overwrite adjacent stack memory locations, potentially corrupting program execution flow and enabling arbitrary code execution. The vulnerability is particularly concerning because it operates at the compilation stage of terminal descriptions, meaning that any application using ncurses could be affected when processing untrusted terminfo data.
The operational impact of CVE-2017-16879 extends beyond simple denial of service scenarios to encompass potential remote code execution capabilities. Attackers can leverage this vulnerability by constructing malicious terminfo files that, when processed by tic, trigger the buffer overflow condition. The vulnerability affects systems where ncurses is used for terminal handling, which includes virtually all unix-like systems and applications that rely on terminal capabilities for user interface elements. The attack vector is particularly dangerous because it can be exploited through legitimate file processing operations, making it difficult to detect and prevent. This vulnerability aligns with CWE-121 stack-based buffer overflow classification and maps to attack techniques in the MITRE ATT&CK framework under privilege escalation and execution categories.
Mitigation strategies for CVE-2017-16879 primarily involve immediate patching of affected ncurses installations to version 6.1 or later, which contains the necessary fixes for the buffer overflow condition. System administrators should also implement strict input validation for any terminfo files that are processed by tic, particularly those received from untrusted sources. Additional defensive measures include restricting tic execution permissions, implementing file integrity monitoring for terminal description files, and establishing secure coding practices that enforce bounds checking in similar buffer manipulation functions. Organizations should also consider implementing network segmentation and access controls to limit exposure of systems that process potentially malicious terminal descriptions. The vulnerability demonstrates the importance of proper input validation and memory safety practices in system libraries that handle user-provided data, reinforcing the need for comprehensive security testing and code review processes in critical infrastructure components.