# CVE-2026-89579

## Summary

- **CVE ID:** CVE-2026-89579
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

bpf: Harden bloom filter sizing and indexing on 32-bit kernels

bloom_map_alloc() has two 32-bit-specific problems when the computed
bitmap reaches the U32_MAX fallback case.

First, BITS_TO_BYTES(U32_MAX) is evaluated with 32-bit arithmetic. The
addition performed by DIV_ROUND_UP wraps, so the map allocates only the
fixed-size bloom filter object while keeping bitset_mask == U32_MAX.
Subsequent updates can then write past the allocated object.

Second, fixing only the allocation size is not sufficient. The bloom hash
is a u32, but set_bit() takes a signed long bit number and x86 test_bit()
eventually feeds the index to variable_test_bit(long, ...). On 32-bit
kernels, hashes in [0x80000000, U32_MAX] therefore become negative bit
offsets. x86 bt/bts with a memory operand interpret those offsets relative
to the supplied base, so a map with bitset_mask == U32_MAX can read or
write before bloom->bitset even after allocating the full 512 MiB bitmap.

Keep the U32_MAX fallback, but split each hash into a word pointer and an
in-word bit number before calling test_bit() or set_bit(). The bitops
argument is then always in [0, BITS_PER_LONG - 1], while BIT_WORD(h) still
selects the intended word in the full bitmap.

Compute the bitset size from (u64)bitset_mask + 1 before passing the final
size to bpf_map_area_alloc(). This fixes the original under-allocation and
keeps the allocated storage consistent with the addressable bitset.

Exploitation note: local privilege escalation is possible on a 32-bit x86
kernel using the under-allocation bug from a binary with CAP_BPF.

## Affected Products

- Linux — Linux (9330986c03006ab1d33d243b7cfe598a7a3c1baa)
- Linux — Linux (5.16)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (6.1.188)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/3b7a13eccfcf97714ffc1ca6aa663d66d4a30e29)
- [CNA](https://git.kernel.org/stable/c/272fcb4ba6fab678db0eb966dc81c4c804bef64a)
- [CNA](https://git.kernel.org/stable/c/dff481e12b3f127739f6a4ea7cef2c25dc12e056)
- [CNA](https://git.kernel.org/stable/c/11c1e836710dcba03e50454a4eedfdbaf8d3050e)
- [CNA](https://git.kernel.org/stable/c/a6183bc683f97f4317f7e84939ca7fff37c5688b)
- [CNA](https://git.kernel.org/stable/c/80551bf8912c42d1e3d55eec6fa3c40f306c3de8)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.17%
- **EPSS Percentile:** 6.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._