CVE-2026-63809
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- CVE-2026-63809
CVE Details
| Release Date: | 2026-07-19 | |
| Impact: | Moderate | What is this? |
Description
In the Linux kernel, the following vulnerability has been resolved:
bpf: use kvfree() for replaced sysctl write buffer
proc_sys_call_handler() allocates its temporary sysctl buffer with
kvzalloc() and passes it to __cgroup_bpf_run_filter_sysctl(). Since
kvzalloc() may fall back to vmalloc() for large allocations, freeing
that buffer with kfree() is wrong and can corrupt memory.
Use kvfree() to safely handle both kmalloc and kvzalloc()/vmalloc
allocations.
The bug was first flagged by an experimental analysis tool we are
developing for kernel memory-management bugs while analyzing
v6.13-rc1. The tool is still under development and is not yet publicly
available. Manual inspection confirms that the bug is still
present in v7.1-rc5.
Reproduced the bug based on v7.1-rc4 in a QEMU x86_64 guest booted with
KASAN and CONFIG_FAILSLAB enabled. To exercise the replacement path, the
test tree also included the accompanying fix for the stale ret == 1
check in __cgroup_bpf_run_filter_sysctl(). The reproducer confines
failslab injections to the proc_sys_call_handler() range, uses
stacktrace-depth=32, and injects fail-nth=1 while writing 8191 bytes to
/proc/sys/kernel/domainname from a task in the target cgroup. Under
that setup, fail-nth=1 triggered the fault:
BUG: unable to handle page fault for address: ffffeb0200024d48
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: Oops: 0000 SMP KASAN NOPTI
CPU: 2 UID: 0 PID: 209 Comm: repro_proc_sys_ Not tainted 7.1.0-rc4-00686-g97625979a5d4 PREEMPT(lazy)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
RIP: 0010:kfree+0x6e/0x510
...
Call Trace:
See more information about CVE-2026-63809 from MITRE CVE dictionary and NIST NVD
NOTE: The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 metrics
| Base Score: | 7.0 |
| Vector String: | CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H |
| Version: | 3.1 |
| Attack Vector: | Local |
| Attack Complexity: | High |
| Privileges Required: | Low |
| User Interaction: | None |
| Scope: | Unchanged |
| Confidentiality Impact: | High |
| Integrity Impact: | High |
| Availability Impact: | High |
Errata information
| Platform | Errata | Release Date |
| Oracle Linux version 8 (kernel-uek) | ELBA-2026-500163 | 2026-08-11 |
| Oracle Linux version 9 (kernel-uek) | ELBA-2026-500163 | 2026-08-11 |
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