{"id":"CVE-2026-43438","state":"PUBLISHED","title":"sched_ext: Remove redundant css_put() in scx_cgroup_init()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nsched_ext: Remove redundant css_put() in scx_cgroup_init()\n\nThe iterator css_for_each_descendant_pre() walks the cgroup hierarchy\nunder cgroup_lock(). It does not increment the reference counts on\nyielded css structs.\n\nAccording to the cgroup documentation, css_put() should only be used\nto release a reference obtained via css_get() or css_tryget_online().\nSince the iterator does not use either of these to acquire a reference,\ncalling css_put() in the error path of scx_cgroup_init() causes a\nrefcount underflow.\n\nRemove the unbalanced css_put() to prevent a potential Use-After-Free\n(UAF) vulnerability.","publishedAt":"2026-05-08T14:22:07.980Z","updatedAt":"2026-08-05T12:27:56.866Z","severity":{"score":7.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"8195136669661fdfe54e9a8923c33b31c92fc1da","status":"affected","lessThan":"cc095cd305fddbe25a968e4a78436ff9476cf0f6","versionType":"git"},{"version":"8195136669661fdfe54e9a8923c33b31c92fc1da","status":"affected","lessThan":"6eaaa67d6998f6c30c462b140db8c062e07ec473","versionType":"git"},{"version":"8195136669661fdfe54e9a8923c33b31c92fc1da","status":"affected","lessThan":"bf50f3285eda8a0173625fcdb5f183f96e1008cd","versionType":"git"},{"version":"8195136669661fdfe54e9a8923c33b31c92fc1da","status":"affected","lessThan":"1336b579f6079fb8520be03624fcd9ba443c930b","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/sched/ext.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.12","versionType":"semver"},{"version":"6.12.78","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.19","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.9","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/sched/ext.c"]}],"references":["https://git.kernel.org/stable/c/cc095cd305fddbe25a968e4a78436ff9476cf0f6","https://git.kernel.org/stable/c/6eaaa67d6998f6c30c462b140db8c062e07ec473","https://git.kernel.org/stable/c/bf50f3285eda8a0173625fcdb5f183f96e1008cd","https://git.kernel.org/stable/c/1336b579f6079fb8520be03624fcd9ba443c930b"],"weaknesses":[],"ingestedAt":"2026-10-29T20:11:57.932Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/43xxx/CVE-2026-43438.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-43438","state":"PUBLISHED","datePublished":"2026-05-08T14:22:07.980Z","dateUpdated":"2026-08-05T12:27:56.866Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-05-01T14:12:56.009Z"},"containers":{"cna":{"title":"sched_ext: Remove redundant css_put() in scx_cgroup_init()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nsched_ext: Remove redundant css_put() in scx_cgroup_init()\n\nThe iterator css_for_each_descendant_pre() walks the cgroup hierarchy\nunder cgroup_lock(). It does not increment the reference counts on\nyielded css structs.\n\nAccording to the cgroup documentation, css_put() should only be used\nto release a reference obtained via css_get() or css_tryget_online().\nSince the iterator does not use either of these to acquire a reference,\ncalling css_put() in the error path of scx_cgroup_init() causes a\nrefcount underflow.\n\nRemove the unbalanced css_put() to prevent a potential Use-After-Free\n(UAF) vulnerability."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"8195136669661fdfe54e9a8923c33b31c92fc1da","status":"affected","lessThan":"cc095cd305fddbe25a968e4a78436ff9476cf0f6","versionType":"git"},{"version":"8195136669661fdfe54e9a8923c33b31c92fc1da","status":"affected","lessThan":"6eaaa67d6998f6c30c462b140db8c062e07ec473","versionType":"git"},{"version":"8195136669661fdfe54e9a8923c33b31c92fc1da","status":"affected","lessThan":"bf50f3285eda8a0173625fcdb5f183f96e1008cd","versionType":"git"},{"version":"8195136669661fdfe54e9a8923c33b31c92fc1da","status":"affected","lessThan":"1336b579f6079fb8520be03624fcd9ba443c930b","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/sched/ext.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.12","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.12","versionType":"semver"},{"version":"6.12.78","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.19","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.9","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/sched/ext.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/cc095cd305fddbe25a968e4a78436ff9476cf0f6"},{"url":"https://git.kernel.org/stable/c/6eaaa67d6998f6c30c462b140db8c062e07ec473"},{"url":"https://git.kernel.org/stable/c/bf50f3285eda8a0173625fcdb5f183f96e1008cd"},{"url":"https://git.kernel.org/stable/c/1336b579f6079fb8520be03624fcd9ba443c930b"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The vulnerable path is reached from local userspace through BPF struct_ops scheduler registration and cgroup state, not by remote packets or adjacent/physical input.\nAC:L - An attacker with the needed BPF access can provide an ops.cgroup_init() callback that succeeds for root and fails for an existing non-root cgroup, directly triggering the bad error path without winning a race.\nPR:L - Loading and attaching sched_ext BPF struct_ops requires local BPF privileges, but these can be delegated via BPF tokens/user-namespace based capability checks in plausible deployments, so this is not necessarily real init-namespace root.\nUI:N - After the attacker has local access and the required BPF ability, exploitation is performed by their own syscalls and does not require a victim user action.\nS:U - The bug corrupts kernel cgroup/scheduler state within the same kernel security authority; it is not a VM escape or another explicit scope boundary crossing.\nC:H - The redundant css_put() can underflow the css refcount and lead to use-after-free of cgroup/task_group state, which is memory corruption that can plausibly enable kernel memory disclosure.\nI:H - A use-after-free in kernel heap-managed scheduler/cgroup objects can plausibly be shaped into arbitrary write or control-flow corruption, so integrity impact is high.\nA:H - Even without full exploitation, the refcount underflow/UAF can corrupt live kernel cgroup state and cause warnings, crashes, or panics."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:27:56.866Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12","versionEndExcluding":"6.12.78"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12","versionEndExcluding":"6.18.19"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12","versionEndExcluding":"6.19.9"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.12","versionEndExcluding":"7.0"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}