CVE-2025-21756: Exploiting a Linux Kernel Vulnerability via vsock
2025-04-30
A researcher discovered a simple Linux kernel vulnerability, CVE-2025-21756, in a KernelCTF submission, allowing privilege escalation via vsock. The exploit centers on a Use After Free (UAF) issue, fixed with only a few lines of code. The researcher analyzed the patch, identified the vulnerability, and attempted a cross-cache attack. However, AppArmor prevented direct exploitation. They cleverly used vsock_diag_dump as a side channel to bypass kASLR and leak kernel addresses. Finally, a carefully crafted ROP chain was used to call `commit_creds` and gain root privileges. The journey was challenging, providing valuable kernel security knowledge.
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