CVE-2016-2090 in libbsd
Summary
by MITRE
Off-by-one vulnerability in the fgetwln function in libbsd before 0.8.2 allows attackers to have unspecified impact via unknown vectors, which trigger a heap-based buffer overflow.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/13/2026
The CVE-2016-2090 vulnerability represents a critical heap-based buffer overflow flaw within the fgetwln function of the libbsd library version 0.8.1 and earlier. This vulnerability stems from an off-by-one error that occurs during the processing of wide character input streams, specifically when reading lines from file descriptors using wide character functions. The flaw manifests in the memory management routines where the function fails to properly account for the null termination character when calculating buffer boundaries, leading to an overwrite condition in heap-allocated memory regions.
The technical implementation of this vulnerability involves the fgetwln function's handling of wide character input where it attempts to read a line of wide characters from a file descriptor while maintaining internal buffer boundaries. When processing input data, the function calculates the required buffer size but incorrectly includes or excludes the null terminator in its boundary calculations, creating a condition where subsequent memory writes can exceed the allocated buffer space. This off-by-one error allows attackers to write data beyond the intended buffer limits, potentially corrupting adjacent heap metadata or other program data structures. The vulnerability's impact is particularly concerning because it operates within the heap memory space, making exploitation more complex but potentially more dangerous than stack-based overflows.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can enable attackers to achieve arbitrary code execution or cause application crashes and denial of service conditions. When exploited successfully, the heap-based buffer overflow can corrupt heap metadata structures such as chunk headers, free lists, or other critical memory management data, leading to unpredictable program behavior or complete system compromise. The unspecified impact mentioned in the vulnerability description reflects the difficulty in determining exact exploitation vectors, as the flaw could potentially be leveraged through multiple attack scenarios including crafted input files, network-based attacks, or privilege escalation opportunities. This vulnerability particularly affects systems that rely heavily on libbsd for wide character string operations and could be especially problematic in server applications, daemons, or any software that processes untrusted input through the fgetwln function.
Mitigation strategies for CVE-2016-2090 primarily focus on updating to libbsd version 0.8.2 or later, where the off-by-one error has been corrected through proper buffer boundary calculations. System administrators should prioritize patching affected systems, particularly those running applications that utilize the vulnerable function, and implement monitoring for any unusual memory allocation patterns or heap corruption indicators. The vulnerability aligns with CWE-121, heap-based buffer overflow, and can be mapped to ATT&CK technique T1059.007 for command and scripting interpreter, as exploitation may involve crafting malicious input to trigger the vulnerable code path. Additional defensive measures include implementing address space layout randomization, stack canaries, and heap hardening techniques, though the most effective approach remains the immediate application of the vendor-provided security patch to eliminate the root cause of the vulnerability.