Stack Corruption via File Descriptor Overflow in libnv

CVE-2026-39457 is a stack corruption vulnerability in libnv's socket data exchange mechanism. The library uses select(2) to monitor file descriptors without validating that descriptor values fall within the FD_SETSIZE limit (1024). When an attacker forces a vulnerable application to allocate file descriptors beyond this threshold—through descriptor exhaustion or inheritance from parent processes—the oversized file descriptor set overflows the stack buffer. This is particularly critical in setuid-root applications where stack corruption can lead to privilege escalation. Any libnv-dependent software handling untrusted network data or running with elevated privileges is at risk, especially in multi-process environments where descriptor leakage is common.

While Casky.ai currently shows zero matching skills for this specific CVE, the underlying attack pattern aligns with resource manipulation and memory corruption detection capabilities within Claude AI's extended reasoning framework. In practice, security practitioners using Casky would identify precursor activities through: (1) Anomalous file descriptor allocation patterns via system call monitoring, (2) Stack-based memory access violations during socket operations, and (3) Privilege escalation attempts following libnv function calls in setuid contexts. A practitioner investigating this vulnerability would correlate suspicious descriptor exhaustion with crashes in setuid processes, then trace execution back to libnv socket handling code. Casky's integration of MITRE ATT&CK techniques—particularly Resource Hijacking and Exploitation for Privilege Escalation—would help contextualize these technical indicators within a broader threat model, even as new skills are developed to specifically address this CWE-121 stack buffer overflow variant.