CVE-2024-50072 x86/bugs: Use code segment selector for VERW operand
A local attacker can trigger a general protection fault and crash the system by executing specific 32-bit operations when VERW-based CPU mitigations are enabled.
- 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-2024-50072?
CVE-2024-50072 is a medium-severity denial of service vulnerability in Linux kernel, published on 29 Oct 2024. 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:
x86/bugs: Use code segment selector for VERW operand
Robert Gill reported below #GP in 32-bit mode when dosemu software was executing vm86() system call:
general protection fault: 0000 [#1] PREEMPT SMP CPU: 4 PID: 4610 Comm: dosemu.bin Not tainted 6.6.21-gentoo-x86 #1 Hardware name: Dell Inc. PowerEdge 1950/0H723K, BIOS 2.7.0 10/30/2010 EIP: restore_all_switch_stack+0xbe/0xcf EAX: 00000000 EBX: 00000000 ECX: 00000000 EDX: 00000000 ESI: 00000000 EDI: 00000000 EBP: 00000000 ESP: ff8affdc DS: 0000 ES: 0000 FS: 0000 GS: 0033 SS: 0068 EFLAGS: 00010046 CR0: 80050033 CR2: 00c2101c CR3: 04b6d000 CR4: 000406d0 Call Trace: show_regs+0x70/0x78 die_addr+0x29/0x70 exc_general_protection+0x13c/0x348 exc_bounds+0x98/0x98 handle_exception+0x14d/0x14d exc_bounds+0x98/0x98 restore_all_switch_stack+0xbe/0xcf exc_bounds+0x98/0x98 restore_all_switch_stack+0xbe/0xcf
This only happens in 32-bit mode when VERW based mitigations like MDS/RFDS are enabled. This is because segment registers with an arbitrary user value can result in #GP when executing VERW. Intel SDM vol. 2C documents the following behavior for VERW instruction:
#GP(0) - If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.
CLEAR_CPU_BUFFERS macro executes VERW instruction before returning to user space. Use %cs selector to reference VERW operand. This ensures VERW will not #GP for an arbitrary user %ds.
[ mingo: Fixed the SOB chain. ]
Which versions are affected by CVE-2024-50072?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-50072?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2024-50072 being exploited?
There is no known exploitation of CVE-2024-50072 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-52077, AZL-52141, BELL-CVE-2024-50072, DEBIAN-CVE-2024-50072, GHSA-643h-952w-33f5, UBUNTU-CVE-2024-50072.