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CVE-2026-89579
bpf: Harden bloom filter sizing and indexing on 32-bit kernels
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem kernel/bpf. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89579 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
kernel/bpf/bloom_filter.c
- What this is
- BPF [GENERAL] (Safe Dynamic Programs and Tools)MAINTAINERS section matched on kernel/bpf/ · bpf@vger.kernel.org · Supported
Check it on the machine
grep -wE 'CONFIG_BPF|CONFIG_BPF_SYSCALL' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switches
- CONFIG_BPF, CONFIG_BPF_SYSCALL
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-11 (37 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 5.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- kernel/bpf
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.16 | 6.1.188 | a6183bc683f9 |
| 5.16 | 6.6.157 | 80551bf8912c |
| 5.16 | 6.12.109 | 3b7a13eccfcf |
| 5.16 | 6.18.50 | 272fcb4ba6fa |
| 5.16 | 7.2.4 | dff481e12b3f |
| 5.16 | 7.3 | 11c1e836710d |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bug is reached only via local bpf(2) syscalls: BPF_MAP_CREATE of BPF_MAP_TYPE_BLOOM_FILTER, then BPF_MAP_UPDATE_ELEM/LOOKUP_ELEM which call bloom_map_push_elem/peek_elem. Per kernel CNA guidance BPF is Local, not network-reachable.
- AC:LAttack complexity, low
- On a 32-bit kernel the attacker deterministically forces the U32_MAX bitmap fallback with a large max_entries so BITS_TO_BYTES wraps and under-allocates; BPF_F_ZERO_SEED and chosen values then drive set_bit/test_bit to selected out-of-bounds indexes with no race or uncontrolled layout.
- PR:LPrivileges required, low
- Creating a bloom-filter map requires CAP_BPF in map_create_alloc (bpf_token_capable). Per kernel guidance this is Low because CAP_BPF is obtainable via user namespaces and BPF token delegation, not only init-namespace root.
- UI:NUser interaction, none
- The attacker creates the undersized bloom map and issues lookup/update syscalls from their own process; no victim action such as mounting a filesystem or opening a file is required.
- S:UScope, unchanged
- The out-of-bounds bit set/test corrupts kernel heap around the undersized bloom object on the same host. This is standard kernel memory corruption and privilege escalation, not a VM escape or IOMMU boundary bypass.
- C:HConfidentiality impact, high
- With bitset_mask==U32_MAX and a near-empty allocation, bloom_map_peek_elem's test_bit is an out-of-bounds kernel bit-read oracle, and the matching OOB writes enable heap disclosure; kernel guidance rates such memory corruption as High confidentiality impact.
- I:HIntegrity impact, high
- bloom_map_push_elem's set_bit writes past (and on 32-bit x86, before) the allocated object across a huge range, a controllable OOB write. The fix commit documents local privilege escalation from CAP_BPF on 32-bit x86.
- A:HAvailability impact, high
- The same unbounded set_bit/test_bit indexes unmapped pages around the undersized kmalloc object and reliably produces a kernel oops or panic, which is High availability impact per kernel guidance.