CVE-2026-89579
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
A vulnerability in the Linux kernel BPF bloom filter sizing and indexing on 32-bit kernels has been fixed. When the bitmap reaches the U32_MAX fallback case, an arithmetic error causes under-allocation, and negative bit offsets allow writes past the allocated object. This enables local privilege escalation on a 32-bit x86 kernel by a process with CAP_BPF.
Risk Assessment
A local attacker with CAP_BPF can exploit this vulnerability to write past allocated memory and escalate privileges on the system. This affects organizations running 32-bit x86 Linux kernels with BPF enabled.
Recommendation
Update the Linux kernel to a version containing the fix that computes the bitset size using (u64)bitset_mask + 1 and splits the hash into a word pointer and in-word bit number. If updating is not possible, restrict granting CAP_BPF to trusted processes.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS