CVE-2026-93127 bpf: Drop scalar id on sign-extending narrowing stack fills
A flaw in the Linux kernel BPF verifier allows out-of-bounds memory access due to incorrect scalar ID handling during sign-extending loads, potentially enabling privilege escalation.
- 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-2026-93127?
CVE-2026-93127 is a high-severity memory corruption 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:
bpf: Drop scalar id on sign-extending narrowing stack fills
When a spilled scalar is filled back with a sign-extending narrowing load (BPF_MEMSX), check_stack_read_fixed_off() copies the spilled register including its scalar id, but coerce_reg_to_size_sx() then sign-extends the filled register's value. If the same slot is also filled with a plain zero-extending load (BPF_MEM), both destination registers share the id yet hold different values. A later 'if <zext-reg> == const' then refines the sign-extended register through sync_linked_regs() to a value it does not have at runtime (e.g. the verifier believes 0x80000000 while the register is 0xffffffff80000000), which can be turned into an out-of-bounds access.
Drop the shared scalar id at the sign-extension site in check_mem_access() when sign extension actually changes the value, mirroring the BPF_MOVSX handling in check_alu_op() (no_sext = reg_umax < 2^(size*8-1)).
Which versions are affected by CVE-2026-93127?
How do I fix CVE-2026-93127?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-93127 being exploited?
There is no known exploitation of CVE-2026-93127 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-93127, GHSA-6crf-588f-8r2f, UBUNTU-CVE-2026-93127.