CVE-2015-8983 in C Library
Summary
by MITRE
Integer overflow in the _IO_wstr_overflow function in libio/wstrops.c in the GNU C Library (aka glibc or libc6) before 2.22 allows context-dependent attackers to cause a denial of service (application crash) or possibly execute arbitrary code via vectors related to computing a size in bytes, which triggers a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 09/10/2020
The vulnerability identified as CVE-2015-8983 represents a critical integer overflow flaw within the GNU C Library's wide string handling functionality. This issue resides in the _IO_wstr_overflow function located in libio/wstrops.c, affecting glibc versions prior to 2.22. The vulnerability manifests when applications process wide character strings through the standard I/O library, creating a scenario where an attacker can manipulate input data to trigger unintended behavior in the underlying memory management system.
The technical flaw stems from improper integer arithmetic during the calculation of buffer sizes when handling wide character strings. When the _IO_wstr_overflow function processes input data, it computes a size in bytes that should represent the required buffer space for wide character operations. However, due to insufficient bounds checking and overflow handling, this computation can produce a value that exceeds the maximum representable integer, leading to a wraparound condition. This integer overflow directly results in a heap-based buffer overflow, where subsequent memory operations write beyond the allocated buffer boundaries, corrupting adjacent memory regions.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to potentially enable arbitrary code execution. Attackers can exploit this flaw by crafting malicious input that triggers the overflow condition during wide string processing operations. When successful, the heap corruption can lead to application crashes, but more critically, it may allow attackers to manipulate program execution flow through controlled memory corruption. This makes the vulnerability particularly dangerous in applications that process untrusted input through standard I/O functions, as it can be leveraged for privilege escalation or remote code execution depending on the target application's context and privileges.
The vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions, and demonstrates characteristics consistent with ATT&CK technique T1059.007 for command and scripting interpreter. The flaw operates at the system library level, making it particularly insidious as it can affect any application linked against the vulnerable glibc version. The context-dependent nature of the vulnerability means that exploitation requires specific conditions related to the application's use of wide character I/O operations, but once triggered, the impact can be severe. Organizations should prioritize patching systems running glibc versions before 2.22, as this vulnerability has been widely exploited in the wild and represents a significant risk to system integrity and availability. The fix implemented in glibc 2.22 includes proper integer overflow detection and handling within the _IO_wstr_overflow function, ensuring that buffer size calculations cannot produce values that would lead to heap corruption.