Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-06-24T00:00:00 kernel: bpf: Enforce regsafe base id consistency for BPF_ADD_CONST scalars 6.4 CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H CWE-386

In the Linux kernel, the following vulnerability has been resolved: bpf: Enforce regsafe base id consistency for BPF_ADD_CONST scalars When regsafe() compares two scalar registers that both carry BPF_ADD_CONST, check_scalar_ids() maps their full compound id (aka base | BPF_ADD_CONST flag) as one idmap entry. However, it never verifies that the underlying base ids, that is, with the flag stripped are consistent with existing idmap mappings. This allows construction of two verifier states where the old state has R3 = R2 + 10 (both sharing base id A) while the current state has R3 = R4 + 10 (base id C, unrelated to R2). The idmap creates two independent entries: A->B (for R2) and A|flag->C|flag (for R3), without catching that A->C conflicts with A->B. State pruning then incorrectly succeeds. Fix this by additionally verifying base ID mapping consistency whenever BPF_ADD_CONST is set: after mapping the compound ids, also invoke check_ids() on the base IDs (flag bits stripped). This ensures that if A was already mapped to B from comparing the source register, any ADD_CONST derivative must also derive from B, not an unrelated C.

A flaw was found in the Linux kernel's Berkeley Packet Filter (BPF) verifier. This vulnerability occurs due to inconsistent base ID mapping when the `regsafe()` function compares scalar registers with `BPF_ADD_CONST` values. This inconsistency allows the BPF verifier to incorrectly succeed in state pruning, which could enable a bypass of its security mechanisms. Such a bypass may lead to unexpected system behavior or potentially allow an attacker to execute unauthorized operations.

This CVE has been rated as Moderate because eBPF (and XDP) is restricted to root-only on Red Hat Enterprise Linux. Red Hat Enterprise Linux 10 Fix deferred kernel Red Hat Enterprise Linux 6 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel Red Hat Enterprise Linux 7 Not affected kernel-rt Red Hat Enterprise Linux 8 Not affected kernel Red Hat Enterprise Linux 8 Not affected kernel-rt Red Hat Enterprise Linux 9 Fix deferred kernel Red Hat Enterprise Linux 9 Fix deferred kernel-rt https://www.cve.org/CVERecord?id=CVE-2026-53081 https://nvd.nist.gov/vuln/detail/CVE-2026-53081 https://lore.kernel.org/linux-cve-announce/2026062407-CVE-2026-53081-4676@gregkh/T