Vulnerability record · CVE-2026-93127 · published 17 September 2026
CVE-2026-93127: In the Linux kernel, the following vulnerability has been resolved: bpf: Drop scalar id on sign-extending nar…
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)).
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)).
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
References
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Source: NIST National Vulnerability Database (record CVE-2026-93127), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.
