Cloudanix VulnDB

CVE-2026-93164

None

CVSS

—

EPSS

0.2%

Published

Sep 17, 2026

CISA due date

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Cloudanix analysis

Schedule a fix SSVC: Track

A Linux kernel bug in debugging features could let certain tracing operations overwrite memory areas that programs rely on, leading to crashes or wrong results.

Exploitation
Local Privilege
Attacker needs
Low Privilege
Complexity
Moderate
Impact
Data Tampering
Component
OS kernel
Class
Memory Corruption
Remediation
Upgrade
Effort
Medium
Patch risk
Low

What it actually does

The optimized uprobe implementation on x86 used a 5-byte NOP that placed a call instruction inside the redzone, allowing the stored return address to overwrite user data that applications may keep there without adjusting RSP.

Why it matters to the business

Systems relying on uprobes or uretprobes for tracing or performance monitoring could experience crashes, data corruption, or unreliable probe results, potentially affecting observability tooling and requiring kernel updates.

How an attack unfolds

An attacker with the ability to place probes on functions would trigger the uprobe path; when the INT3 is hit the trampoline call would clobber the redzone, leading to memory corruption or crashes in affected user code.

How to fix it

Update the Linux kernel to a version containing the nop10-based uprobe optimization and the associated is_prefix_bad and error code changes.

How to confirm the fix worked

Confirm the kernel version includes the nop10 transformation and that uprobe performance metrics show the nop10 variant; verify syscall error returns -EPROTO when called from the trampoline.

Typical attack path

  1. Install an optimized uprobe on a target function using the 5-byte NOP sequence
  2. Trigger execution that hits the INT3 breakpoint
  3. Execute the call from within the redzone without RSP adjustment
  4. Observe corruption of user data or subsequent crashes

How to detect it

Look in kernel logs for uprobe-related faults or redzone corruption symptoms; examine probe installation paths and any associated crashes around uprobe trampolines.

What your security team should do

  • Prioritize kernel updates on systems using uprobes or BPF tracing
  • Monitor for crashes or unexpected behavior in applications with active probes
  • Test probe workloads after upgrade to confirm stability

The record

In the Linux kernel, the following vulnerability has been resolved: uprobes/x86: Move optimized uprobe from nop5 to nop10 Andrii reported an issue with optimized uprobes [1] that can clobber redzone area with call instruction storing return address on stack where user code may keep temporary data without adjusting rsp. Fixing this by moving the optimized uprobes on top of 10-bytes nop instruction, so we can squeeze another instruction to escape the redzone area before doing the call, like: lea -0x80(%rsp), %rsp call tramp Note the lea instruction is used to adjust the rsp register without changing the flags. We use nop10 and following transformation to optimized instructions above and back as suggested by Peterz [2]. Optimize path (int3_update_optimize): 1) Initial state after set_swbp() installed the uprobe: cc 2e 0f 1f 84 00 00 00 00 00 From offset 0 this is INT3 followed by the tail of the original 10-byte NOP. After a previous unoptimization bytes 5..9 may still contain the old call instruction, which remains valid for threads already there. 2) Rewrite the LEA tail and call displacement: cc [8d 64 24 80 e8 d0 d1 d2 d3] From offset 0 this traps on the uprobe INT3. Bytes 1..9 are not executable entry points while byte 0 is trapped. 3) Publish the first LEA byte: [48] 8d 64 24 80 e8 d0 d1 d2 d3 From offset 0 this is: lea -0x80(%rsp), %rsp call <uprobe-trampoline> Unoptimize path (int3_update_unoptimize): 1) Initial optimized state: 48 8d 64 24 80 e8 d0 d1 d2 d3 Same as 3) above. 2) Trap new entries before restoring the NOP bytes: [cc] 8d 64 24 80 e8 d0 d1 d2 d3 From offset 0 this traps. A thread that had already executed the LEA can still reach the intact CALL at offset 5. 3) Restore bytes 1..4 of the original NOP while keeping byte 0 trapped and byte 5 as CALL. cc [2e 0f 1f 84] e8 d0 d1 d2 d3 From offset 0 this still traps. Offset 5 is still the CALL for any thread that was already past the first LEA byte. 4) Publish the first byte of the original NOP: [66] 2e 0f 1f 84 e8 d0 d1 d2 d3 From offset 0 this is the restored 10-byte NOP; the CALL opcode and displacement are now only NOP operands. Offset 5 still decodes as CALL for a thread that was already there. Tthere is only a single target uprobe-trampoline for the given nop10 instruction address, so the CALL instruction will not be changed across unoptimization/optimization cycles. Therefore, any task that is preempted at the CALL instruction is guaranteed to observe that CALL and not anything else. Note as explained in [2] we need to use following nop10: PF1 PF2 ESC NOPL MOD SIB DISP32 NOP10: 0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00 -- cs nopw 0x00000000(%rax,%rax,1) which means we need to allow 0x2e prefix which maps to INAT_PFX_CS attribute in is_prefix_bad function. Also changing the uprobe syscall error when called out of uprobe trampoline to -EPROTO, so we are able to detect the fixed kernel. The optimized uprobe performance stays the same: uprobe-nop : 3.129 ± 0.013M/s uprobe-push : 3.045 ± 0.006M/s uprobe-ret : 1.095 ± 0.004M/s --> uprobe-nop10 : 7.170 ± 0.020M/s uretprobe-nop : 2.143 ± 0.021M/s uretprobe-push : 2.090 ± 0.000M/s uretprobe-ret : 0.942 ± 0.000M/s --> uretprobe-nop10: 3.381 ± 0.003M/s usdt-nop : 3.245 ± 0.004M/s --> usdt-nop10 : 7.256 ± 0.023M/s [1] https://lore.kernel.org/bpf/20260509003146.976844-1-andrii@kernel.org/ [2] https://lore.kernel.org/bpf/20260518104306.GU3102624@noisy.programming.kicks-ass.net/#t

Affected packages

Ecosystem Package Introduced Fixed