August 9, 2025 — A essential vulnerability within the Linux kernel, recognized as CVE-2025-38236, has uncovered a flaw that would permit attackers to escalate privileges from throughout the Chrome renderer sandbox on Linux techniques.
Google Undertaking Zero researcher Jann Horn Found the bug impacts Linux kernels model 6.9 and above, stemming from the obscure MSG_OOB (out-of-band) function in UNIX area sockets.
This discovering underscores the dangers posed by esoteric kernel options and highlights gaps in browser sandbox safety.
Uncovering the MSG_OOB Vulnerability
The vulnerability, recognized throughout a code overview in early June, originates from a flaw within the MSG_OOB implementation, launched in Linux 5.15 in 2021.
Although not often used exterior particular Oracle merchandise, MSG_OOB was enabled by default in kernels supporting UNIX sockets and was accessible inside Chrome’s renderer sandbox as a consequence of unfiltered syscall flags.
The bug allows a use-after-free (UAF) situation, which Horn demonstrated will be triggered with a easy sequence of socket operations, probably permitting attackers to control kernel reminiscence and achieve elevated privileges.
The Linux kernel has since been patched, and Chrome has blocked MSG_OOB messages in its renderer sandbox to mitigate the problem.
Horn’s exploit, detailed on Google Undertaking Zero’s bug tracker, exhibits how an attacker may escalate from native code execution within the Chrome renderer sandbox to kernel-level management on a Debian Trixie system operating x86-64 structure.
By exploiting a UAF, the assault leverages a learn primitive to repeat arbitrary kernel reminiscence to person house, navigating usercopy hardening restrictions.
Methods like reallocating freed reminiscence as pipe pages or kernel stacks, mixed with web page desk manipulation and mprotect() for delay injection, allow exact reminiscence corruption.
Notably, the exploit makes use of Debian’s CONFIG_RANDOMIZE_KSTACK_OFFSET function, turning a safety mitigation into a bonus for aligning reminiscence targets.
Challenges in Fuzzing and Sandbox Design
The vulnerability was initially noticed throughout Horn’s overview of a brand new kernel function, with a associated subject later caught by Google’s syzkaller fuzzing device in August 2024.
The primary bug required six syscalls to set off, whereas a second, extra complicated subject discovered by Horn wanted eight, revealing the issue fuzzers face in exploring complicated kernel knowledge constructions like socket buffers (SKBs).
Horn means that fuzzers may enhance by focusing on particular kernel subsystems to raised uncover such vulnerabilities.
The exploit additionally exposes the intensive kernel interfaces accessible in Chrome’s Linux renderer sandbox, together with nameless VMAs, UNIX sockets, pipes, and syscalls like sendmsg() and mprotect().
Many of those interfaces are pointless for renderer performance, unnecessarily increasing the assault floor.
Previous Chrome vulnerabilities involving futex(), memfd_create(), and pipe2() additional spotlight how obscure kernel options can introduce dangers when uncovered in sandboxes.
Horn’s findings additionally query the effectiveness of probabilistic mitigations, like per-syscall stack randomization, towards attackers with arbitrary learn primitives, as these will be bypassed by repeatedly checking randomization outcomes.
The invention requires stricter sandbox restrictions and a reevaluation of kernel options uncovered to unprivileged processes.
Horn plans a deeper evaluation of Chrome’s Linux renderer sandbox in a future report. Linux customers are urged to use the most recent kernel patches, and builders ought to scrutinize esoteric kernel options in core system interfaces.
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