7.8

CVE-2026-63809: linux Out-of-bounds Write

CVSS: 7.8v3.1HighAwaiting analysis
AliasesUBUNTU-CVE-2026-63809DEBIAN-CVE-2026-63809
Published 19-07-2026Last modified 19-10-2026
Open JSON

Vulnerability summary

CVE-2026-63809 is a high (CVSS 7.8) Out-of-bounds Write vulnerability in linux. EPSS estimates a 0.15% chance of exploitation in the next 30 days, higher than 4.1% of scored vulnerabilities.

Overall risk
31/100
0100
Medium · default modelHow is this calculated?
CVSS score
7.8/10
010
High · v3.1 (CVE.org)
EPSS score
0.15%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 33 · Related 32
MGASA-2026-0312OPENSUSE-SU-2026:11339-1OPENSUSE-SU-2026:21555-1SUSE-SU-2026:23066-1SUSE-SU-2026:23068-1SUSE-SU-2026:23193-1

Timeline

  1. 19-07-2026
    PublishedVulnerability first disclosed.
  2. 19-10-2026
    Last modifiedVulnerability information updated.

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: <TASK> ? __cgroup_bpf_run_filter_sysctl+0x626/0xc30 __cgroup_bpf_run_filter_sysctl+0x74d/0xc30 ? __pfx___cgroup_bpf_run_filter_sysctl+0x10/0x10 ? srso_return_thunk+0x5/0x5f ? __kvmalloc_node_noprof+0x345/0x870 ? proc_sys_call_handler+0x250/0x480 ? srso_return_thunk+0x5/0x5f proc_sys_call_handler+0x3a2/0x480 ? __pfx_proc_sys_call_handler+0x10/0x10 ? srso_return_thunk+0x5/0x5f ? selinux_file_permission+0x39f/0x500 ? srso_return_thunk+0x5/0x5f ? lock_is_held_type+0x9e/0x120 vfs_write+0x98e/0x1000 ... </TASK> With this fix applied on top of the same test setup, rerunning the reproducer with fail-nth=1 yields no corresponding Oops reports.

CVSS metrics

5 scores · 4 sources · 2 versions

EPSS trend

Probability

0.15%

Chance of exploitation in the next 30 days

Percentile

4%

Versus all other CVEs

30-day change

0.00 pp

From 0.15% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.15%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Ubuntu157 products
  • linuxAll versions (No fix recorded) | < 5.15.0-198.208 | < 6.8.0-147.147 | < 7.0.0-31.31
  • linux-allwinner-5.19All versions (No fix recorded)
  • linux-awsAll versions (No fix recorded) | < 5.15.0-1117.124 | < 6.8.0-1067.70 | < 7.0.0-1012.12
  • linux-aws-5.0All versions (No fix recorded)
  • linux-aws-5.11All versions (No fix recorded)
Debian1 product
  • linux< 6.1.177-1 | < 6.12.95-1 | < 7.1.3-1
Linux1 product
  • linux≥ b7925acd82926ebbf94a0f0783a3961f4e558856, < d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e | ≥ 4508943794efdd94171549c0bd52810e2f4ad9fe, < 77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2 | ≥ 4508943794efdd94171549c0bd52810e2f4ad9fe, < e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2 | ≥ 4508943794efdd94171549c0bd52810e2f4ad9fe, < 81fc9a13acae99966232f0e055eb2e445263b89a | ≥ 4508943794efdd94171549c0bd52810e2f4ad9fe, < 838fe9c28121777c59a9406710a68fcf77bb8017 | ≥ 4508943794efdd94171549c0bd52810e2f4ad9fe, < 65bd0c0afb0e1bf3287458e342429b069624f7d4 | ≥ 4508943794efdd94171549c0bd52810e2f4ad9fe, < 70df4de46577fab5e25418f014583155a147c902 | ≥ 4508943794efdd94171549c0bd52810e2f4ad9fe, < 4c21b5927d4364bfe7365f2700da5fea0ed0d004 | 66258ab303588936ee1ee0794d9a271be24f73cb | ≥ 5.10.20, < 5.10.260 | ≥ 5.11.3, < 5.12 | 5.12

3 vendors · 159 products

References

32 links
Show all 32 references