CVE-2026-93167 csky: Fix a4/a5 restoration in syscall trace path
A local attacker can cause denial of service by triggering corrupted syscall arguments in the C-SKY architecture trace path.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-93167?
CVE-2026-93167 is a vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
csky: Fix a4/a5 restoration in syscall trace path
The syscall trace path reloads syscall arguments from pt_regs before calling the syscall handler. On C-SKY ABIv2, the 5th and 6th syscall arguments are prepared as stack arguments before invoking syscallid.
The current code adjusts sp before loading LSAVE_A4 and LSAVE_A5. Since those offsets are relative to the original pt_regs base, loading them after changing sp fetches the wrong slots. As a result, traced syscalls that use the 5th or 6th argument may receive corrupted arguments.
This is visible with mmap2(), which takes six arguments. A small PTRACE_SYSCALL reproducer opens a file and maps one page with:
mmap(NULL, 4096, PROT_READ | PROT_EXEC, MAP_PRIVATE, fd, 0)
Before the fix, the traced child fails the mmap and exits with 12. After the fix, the mapping succeeds and the child exits with 0.
Fix the trace path by loading a4/a5 from pt_regs before changing sp.
Tested on: ck860f, linux-4.19.15, C-SKY abiv2
Which versions are affected by CVE-2026-93167?
How do I fix CVE-2026-93167?
Apply the vendor's patch.
Is CVE-2026-93167 being exploited?
There is no known exploitation of CVE-2026-93167 in the wild and no public exploit code.
Sources
Also known as AZL-102876, BELL-CVE-2026-93167, DEBIAN-CVE-2026-93167, GHSA-fgg4-f5v2-253f, UBUNTU-CVE-2026-93167.