{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-63802", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T07:54:57.013Z", "datePublished": "2026-07-19T12:02:08.020Z", "dateUpdated": "2026-08-17T04:51:07.787Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-17T04:51:07.787Z"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nblk-cgroup: fix UAF in __blkcg_rstat_flush()\n\nWhen multiple blkgs in the same blkcg are released concurrently,\na use-after-free can occur. The race happens when one blkg's\n__blkcg_rstat_flush() removes another blkg's iostat entries via\nllist_del_all(). The second blkg sees an empty list and proceeds\nto free itself while the first is still iterating over its entries.\n\nMove the flush from __blkg_release() (RCU callback) to blkg_release()\n(before call_rcu). This ensures the RCU grace period waits for any\nconcurrent flush's rcu_read_lock() section to complete before freeing."}], "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 - Exploitation requires local cgroup management (rmdir on cgroupfs) and concurrent block I/O to populate per-blkcg rstat lists; the vulnerable code is in the block cgroup teardown path, not in any network protocol handler.\nAC:L - The attacker controls both sides of the race by issuing I/O on multiple block devices to create multiple blkgs with pending stats, then concurrently destroying the cgroup to trigger parallel blkg_release() calls on multiple CPUs.\nPR:L - Triggering cgroup deletion and block I/O requires only delegated cgroup write access or namespace/container root (CAP_SYS_ADMIN in a user namespace), not init-namespace root; this is routinely available in containers, Kubernetes pods, and systemd user cgroup hierarchies.\nUI:N - No victim interaction is required; the attacker programmatically performs I/O and cgroup teardown from their own process or container.\nS:U - The UAF corrupts kernel heap memory within the same kernel security domain; it does not inherently cross a VM, container, or IOMMU boundary without a separate privilege-escalation step.\nC:H - The use-after-free dereferences freed blkg structures and associated iostat data during list iteration, enabling arbitrary kernel memory read primitives typical of slab UAF bugs.\nI:H - UAF on kmalloc-allocated blkg objects allows heap grooming and write through dangling pointers, which can be leveraged for arbitrary kernel memory modification or code execution.\nA:H - Concurrent use-after-free during blkg teardown can cause immediate kernel oops/panic from accessing freed memory, and repeated triggering enables reliable denial of service."}]}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["block/blk-cgroup.c"], "versions": [{"version": "20cb1c2fb7568a6054c55defe044311397e01ddb", "lessThan": "96e545410c4f74c89d496c1d5d9ef8d08f14368b", "status": "affected", "versionType": "git"}, {"version": "20cb1c2fb7568a6054c55defe044311397e01ddb", "lessThan": "bbebd9425cad3573d1527441753899b926525a0f", "status": "affected", "versionType": "git"}, {"version": "20cb1c2fb7568a6054c55defe044311397e01ddb", "lessThan": "5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6", "status": "affected", "versionType": "git"}, {"version": "20cb1c2fb7568a6054c55defe044311397e01ddb", "lessThan": "afebe44facc48a61761e885bbb7f0380d4a603ec", "status": "affected", "versionType": "git"}, {"version": "20cb1c2fb7568a6054c55defe044311397e01ddb", "lessThan": "0ab5ee5a1badb58cbb2242617cb01a4972b1f2a2", "status": "affected", "versionType": "git"}, {"version": "0f6090d90f627d8c58f939067d6c6821ce1b3c68", "status": "affected", "versionType": "git"}, {"version": "6.3.9", "lessThan": "6.4", "status": "affected", "versionType": "semver"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["block/blk-cgroup.c"], "versions": [{"version": "6.4", "status": "affected"}, {"version": "0", "lessThan": "6.4", "status": "unaffected", "versionType": "semver"}, {"version": "6.6.144", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.12.95", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.18.38", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.1.3", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.2", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "6.6.144"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "6.12.95"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "6.18.38"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "7.1.3"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "7.2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3.9"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/96e545410c4f74c89d496c1d5d9ef8d08f14368b"}, {"url": "https://git.kernel.org/stable/c/bbebd9425cad3573d1527441753899b926525a0f"}, {"url": "https://git.kernel.org/stable/c/5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6"}, {"url": "https://git.kernel.org/stable/c/afebe44facc48a61761e885bbb7f0380d4a603ec"}, {"url": "https://git.kernel.org/stable/c/0ab5ee5a1badb58cbb2242617cb01a4972b1f2a2"}], "title": "blk-cgroup: fix UAF in __blkcg_rstat_flush()", "x_generator": {"engine": "bippy-1.2.0"}}}}

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The race happens when one blkg's\n__blkcg_rstat_flush() removes another blkg's iostat entries via\nllist_del_all(). The second blkg sees an empty list and proceeds\nto free itself while the first is still iterating over its entries.\n\nMove the flush from __blkg_release() (RCU callback) to blkg_release()\n(before call_rcu). This ensures the RCU grace period waits for any\nconcurrent flush's rcu_read_lock() section to complete before freeing."}], "id": "CVE-2026-63802", "lastModified": "2026-08-17T05:17:16.727", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 7.8, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 5.9, "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary"}]}, "published": "2026-07-19T12:16:52.847", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/0ab5ee5a1badb58cbb2242617cb01a4972b1f2a2"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/5e5b7f2ef854936e95dceb6a2fdfefcb7152d2c6"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/96e545410c4f74c89d496c1d5d9ef8d08f14368b"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/afebe44facc48a61761e885bbb7f0380d4a603ec"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/bbebd9425cad3573d1527441753899b926525a0f"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-416"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: blk-cgroup: fix UAF in __blkcg_rstat_flush()", "id": "2502251", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2502251"}, "csaw": false, "cvss3": {"cvss3_base_score": "7.0", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H", "status": "draft"}, "cwe": "CWE-825", "details": ["In the Linux kernel, the following vulnerability has been resolved:\nblk-cgroup: fix UAF in __blkcg_rstat_flush()\nWhen multiple blkgs in the same blkcg are released concurrently,\na use-after-free can occur. The race happens when one blkg's\n__blkcg_rstat_flush() removes another blkg's iostat entries via\nllist_del_all(). The second blkg sees an empty list and proceeds\nto free itself while the first is still iterating over its entries.\nMove the flush from __blkg_release() (RCU callback) to blkg_release()\n(before call_rcu). This ensures the RCU grace period waits for any\nconcurrent flush's rcu_read_lock() section to complete before freeing.", "A flaw was found in the Linux kernel's block input/output control group (blk-cgroup) component. This vulnerability, a Use-After-Free (UAF), occurs when multiple block control groups are released at the same time. A race condition allows one group to remove another's entries while it is still in use, leading to premature memory deallocation. This can result in system instability or a denial of service."], "name": "CVE-2026-63802", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Out of support scope", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2026-07-19T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-63802\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-63802\nhttps://lore.kernel.org/linux-cve-announce/2026071901-CVE-2026-63802-1c53@gregkh/T"], "threat_severity": "Moderate"}

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