Bug 2536158 (CVE-2026-93127)

Summary: CVE-2026-93127 kernel: bpf: Drop scalar id on sign-extending narrowing stack fills
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's Berkeley Packet Filter (BPF) subsystem. Incorrect handling of scalar identifiers during sign-extending and zero-extending stack operations can lead to a discrepancy between the BPF verifier's understanding of a register's value and its actual runtime value. This vulnerability could allow a local attacker to achieve an out-of-bounds memory access, potentially leading to information disclosure or denial of service.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-09-17 16:41:01 UTC 
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)).
Comment 1 gkamathe 2026-09-18 17:19:46 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-93127.mbox