CVE-2026-89984 perf/x86/intel: Fix kernel address leakages in LBR stack
Local attackers can leak kernel memory addresses via Intel LBR stack filtering flaws, aiding privilege escalation or bypassing KASLR.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89984?
CVE-2026-89984 is a vulnerability in Linux, published on 16 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
perf/x86/intel: Fix kernel address leakages in LBR stack
Before Arch LBR gained CPL filtering support, a user-only branch stack could still contain kernel addresses. As a result, kernel branch records may be exposed to user space even when PERF_SAMPLE_BRANCH_USER is requested.
For example, on Intel Tiger Lake, the following command can still report SYSRET/ERET entries with kernel-space from addresses:
$ ./perf record -e cycles:p -o - --branch-filter any,save_type,u -- \ ./perf bench syscall basic --loop 1000 | \ ./perf script -i - --fields brstack|tr ' ' '\n'| \ grep -E '0x[89a-f][0-9a-f]{15}'
Total time: 0.000 [sec]
0.219000 usecs/op 4,566,210 ops/sec [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.551 MB - ] 0xffffffff93c001c8/0x7f12a2b1d647/P/-/-/16959/SYSRET/- 0xffffffff93c001c8/0x7f12a2b1d5c2/P/-/-/17535/SYSRET/- 0xffffffff93c01928/0x7f12a2861000/P/-/-/6719/ERET/- 0xffffffff93c01928/0x7f12a297a000/P/-/-/8575/ERET/-
The problem is that intel_pmu_lbr_filter() does not fully validate the privilege level of sampled entries. It filters some mismatches based on the branch type and the to address, but it does not reject entries whose from address violates the requested branch privilege filter.
Fix this by extending software filtering to validate both from and to addresses against br_sel. Any LBR entry contains kernel address does not match the requested user filter is dropped. This prevents kernel addresses from appearing in user-only branch stacks.
Which versions are affected by CVE-2026-89984?
How do I fix CVE-2026-89984?
Apply the vendor's patch.
Is CVE-2026-89984 being exploited?
There is no known exploitation of CVE-2026-89984 in the wild and no public exploit code.
Sources
Also known as AZL-101672, BELL-CVE-2026-89984, DEBIAN-CVE-2026-89984, GHSA-jjjc-8r8p-gw7x, UBUNTU-CVE-2026-89984.