CVE-2026-97399 in glibc
Summary
by MITRE • 09/28/2026
The strncasecmp function in the GNU C Library 2.24 and later optimized for the Power8 architecture may read one byte beyond the input size limit, which may crash a program when that byte is not readable.
This condition may happen when the input strings to the strncasecmp function are attacker controlled in an application and they match all the way up to the edge of their page and the neighbouring page is either not mapped or is not readable.
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Analysis
by VulDB Data Team • 09/28/2026
The GNU C Library version 2.24 introduced performance optimizations for Power8 architecture that inadvertently created a memory safety vulnerability within the strncasecmp function. This specific implementation flaw allows the application to read one byte beyond the specified length limit of the input strings under certain conditions. The root cause lies in how the optimized assembly code handles string comparison boundaries on this particular hardware platform, where loop unrolling or vectorized operations may access memory locations that fall outside the explicitly defined buffer limits if not properly guarded by boundary checks at every iteration step.
This vulnerability manifests when two attacker-controlled strings are passed to strncasecmp and their content matches exactly up to the very end of a memory page. In such scenarios, the function attempts to read an additional byte to complete its comparison logic or due to alignment padding requirements inherent in the Power8 instruction set. If this adjacent byte resides on a neighboring memory page that is either unmapped or marked as non-readable by the operating system's virtual memory manager, the hardware triggers a segmentation fault. This results in an immediate crash of the affected application process rather than returning a comparison result or handling the error gracefully.
From a security perspective, this issue represents a classic out-of-bounds read vulnerability classified under CWE-125: Out-of-bounds Read. The potential impact is primarily denial of service against applications that rely on string comparisons for critical logic paths and do not implement robust exception handling around library calls involving user-supplied data. While the immediate effect is typically a crash, in more complex environments where memory layout can be influenced by an attacker, such out-of-bounds reads could potentially leak sensitive information from adjacent memory regions if those pages happen to contain readable but unintended data. This aligns with ATT&CK technique T1083: File and Directory Discovery, as the vulnerability enables indirect probing of system memory structure through controlled crashes or error messages that reveal page boundaries.
Mitigation strategies should focus on updating the GNU C Library to a patched version where this architectural-specific optimization has been corrected to include proper boundary checks before accessing any byte beyond the specified length. Applications utilizing strncasecmp with untrusted input must also implement defensive programming practices, such as validating string lengths prior to invocation and ensuring that buffers are allocated with sufficient padding or guard pages if possible. Additionally, enabling Address Sanitizer during development testing can help identify similar off-by-one errors in custom code paths before deployment. System administrators should prioritize patching systems running Power8 architecture with vulnerable glibc versions to prevent potential service disruptions caused by maliciously crafted inputs designed to trigger these memory access violations.