CVE-2026-72111: bpf: Reset register bounds before narrowing retval range in check_mem_access()

Vulnerability summary

CVE-2026-72111 is a high (CVSS 8.8) vulnerability in linux. EPSS estimates a 0.18% chance of exploitation in the next 30 days, higher than 7.1% of scored vulnerabilities.

Timeline

1. 15-08-2026
   PublishedVulnerability first disclosed.
2. 16-10-2026
   Last modifiedVulnerability information updated.

Description

In the Linux kernel, the following vulnerability has been resolved: bpf: Reset register bounds before narrowing retval range in check_mem_access() When the BPF verifier processes a context load of an LSM hook return value, it calls __mark_reg_s32_range() to narrow the register to the hook's valid range. However, __mark_reg_s32_range() intersects the new range with the register's existing bounds using max_t()/min_t() rather than replacing them. If the destination register carries stale bounds from a prior instruction (e.g. BPF_MOV64_IMM), the intersection can produce a range narrower than reality. The verifier then believes it knows the register's exact value, while at runtime the actual hook return value is loaded, creating a verifier/runtime mismatch that can be used to bypass BPF memory safety checks. The else branch already calls mark_reg_unknown() to reset register state before any narrowing. Apply the same reset in the is_retval path so stale bounds are cleared before __mark_reg_s32_range() intersects.

No weakness data has been published for this record.