CVE-2026-63951

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-63951", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T07:54:57.023Z", "datePublished": "2026-07-19T14:55:44.105Z", "dateUpdated": "2026-08-05T12:37:36.330Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:37:36.330Z"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nzram: fix use-after-free in zram_writeback_endio\n\nA crash was observed in zram_writeback_endio due to a NULL pointer\ndereference in wake_up. The root cause is a race condition between the\nbio completion handler (zram_writeback_endio) and the writeback task.\n\nIn zram_writeback_endio, wake_up() is called on &wb_ctl->done_wait after\nreleasing wb_ctl->done_lock. This creates a race window where the\nwriteback task can see num_inflight become 0, return, and free wb_ctl\nbefore zram_writeback_endio calls wake_up().\n\nCPU 0 (zram_writeback_endio) CPU 1 (writeback_store)\n============================ ============================\n zram_writeback_slots\n zram_submit_wb_request\n zram_submit_wb_request\n wait_event(wb_ctl->done_wait)\nspin_lock(&wb_ctl->done_lock);\nlist_add(&req->entry, &wb_ctl->done_reqs);\nspin_unlock(&wb_ctl->done_lock);\nwake_up(&wb_ctl->done_wait);\n zram_complete_done_reqs\nspin_lock(&wb_ctl->done_lock);\nlist_add(&req->entry, &wb_ctl->done_reqs);\nspin_unlock(&wb_ctl->done_lock);\n while (num_inflight) > 0)\n spin_lock(&wb_ctl->done_lock);\n list_del(&req->entry);\n spin_unlock(&wb_ctl->done_lock);\n // num_inflight becomes 0\n atomic_dec(num_inflight);\n\n // Leave zram_writeback_slots\n // Free wb_ctl\n release_wb_ctl(wb_ctl);\n// UAF crash!\nwake_up(&wb_ctl->done_wait);\n\nThis patch fixes this race by using RCU. By protecting wb_ctl with\nrcu_read_lock() in zram_writeback_endio and using kfree_rcu() to free it,\nwe ensure that wb_ctl remains valid during the execution of\nzram_writeback_endio."}], "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 code runs only in the zram writeback path (`writeback_store` \u2192 `zram_writeback_slots` \u2192 `zram_submit_wb_request` \u2192 `zram_writeback_endio`), reachable via local sysfs writes or system daemons that invoke the same sysfs interface; there is no network, Bluetooth, or physical-device entry point.\nAC:L - This is a use-after-free race between batched bio completion handlers and writeback teardown; with default `writeback_batch_size` of 32 the attacker can drive concurrent inflight bios and repeatedly trigger writeback (directly as root or indirectly on Android via memory-pressure-driven `mmd` maintenance), controlling both sides of the race.\nPR:L - On Android phones\u2014the highest-impact deployment\u2014an unprivileged app can induce memory pressure that causes the memory management daemon to invoke `/sys/block/zram0/writeback` without attacker root; alternatively a local admin can write the sysfs attribute directly, but no capability beyond a basic local user is required in the primary mobile scenario.\nUI:N - Exploitation requires no victim interaction beyond normal system operation; automated writeback on memory pressure or attacker-initiated sysfs writeback proceeds without the user mounting filesystems, opening files, or taking deliberate action.\nS:U - Successful exploitation corrupts kernel heap memory and can lead to privilege escalation or kernel crash, but does not cross a VM, IOMMU, or sandbox security boundary beyond standard kernel compromise.\nC:H - The bug is a slab use-after-free on `struct zram_wb_ctl`; `wake_up()` operates on a freed `wait_queue_head_t`, enabling arbitrary kernel memory reads through heap reuse and controlled corruption of wait-queue state.\nI:H - Use-after-free on a kmalloc'd control structure allows heap spraying and corruption of `wait_queue_head_t` and adjacent slab objects, providing a plausible path to arbitrary kernel writes and code execution.\nA:H - A production crash was already observed as a NULL pointer dereference in `wake_up()` during the race, and the underlying use-after-free can reliably cause kernel oops/panic even when not fully weaponized for code execution."}]}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["drivers/block/zram/zram_drv.c"], "versions": [{"version": "f405066a1f0db818270f49a5e96be329bcabde1e", "lessThan": "ebe2cbefc86291fa7f386447a81995640df4e2fd", "status": "affected", "versionType": "git"}, {"version": "f405066a1f0db818270f49a5e96be329bcabde1e", "lessThan": "bf62f69574b19720ae5fbbbcdf24a0c4e3e05e43", "status": "affected", "versionType": "git"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["drivers/block/zram/zram_drv.c"], "versions": [{"version": "6.19", "status": "affected"}, {"version": "0", "lessThan": "6.19", "status": "unaffected", "versionType": "semver"}, {"version": "7.0.12", "lessThanOrEqual": "7.0.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.1", "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": "6.19", "versionEndExcluding": "7.0.12"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "7.1"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/ebe2cbefc86291fa7f386447a81995640df4e2fd"}, {"url": "https://git.kernel.org/stable/c/bf62f69574b19720ae5fbbbcdf24a0c4e3e05e43"}], "title": "zram: fix use-after-free in zram_writeback_endio", "x_generator": {"engine": "bippy-1.2.0"}}}}

{}

{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Linux", "programFiles": ["drivers/block/zram/zram_drv.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"lessThan": "ebe2cbefc86291fa7f386447a81995640df4e2fd", "status": "affected", "version": "f405066a1f0db818270f49a5e96be329bcabde1e", "versionType": "git"}, {"lessThan": "bf62f69574b19720ae5fbbbcdf24a0c4e3e05e43", "status": "affected", "version": "f405066a1f0db818270f49a5e96be329bcabde1e", "versionType": "git"}]}, {"defaultStatus": "affected", "product": "Linux", "programFiles": ["drivers/block/zram/zram_drv.c"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"status": "affected", "version": "6.19"}, {"lessThan": "6.19", "status": "unaffected", "version": "0", "versionType": "semver"}, {"lessThanOrEqual": "7.0.*", "status": "unaffected", "version": "7.0.12", "versionType": "semver"}, {"lessThanOrEqual": "*", "status": "unaffected", "version": "7.1", "versionType": "original_commit_for_fix"}]}], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "matchCriteriaId": "9161A938-0FA8-44BC-95FE-C5A271601AB3", "versionEndExcluding": "7.0.12", "versionStartIncluding": "6.19", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:*", "matchCriteriaId": "B1EF7059-E670-45F4-B422-54C40FA86390", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:*", "matchCriteriaId": "0D38F0BF-A728-4133-A358-D44A2F7EE6D6", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc3:*:*:*:*:*:*", "matchCriteriaId": "EC732D08-5F7B-46D9-B154-E60C7F4F0A97", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc4:*:*:*:*:*:*", "matchCriteriaId": "E5910A9D-F60A-409A-B486-FE66BFEBA9B9", "vulnerable": true}, {"criteria": "cpe:2.3:o:linux:linux_kernel:7.1:rc5:*:*:*:*:*:*", "matchCriteriaId": "81DFF19E-9CF8-49C6-8C36-1E4038622933", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nzram: fix use-after-free in zram_writeback_endio\n\nA crash was observed in zram_writeback_endio due to a NULL pointer\ndereference in wake_up. The root cause is a race condition between the\nbio completion handler (zram_writeback_endio) and the writeback task.\n\nIn zram_writeback_endio, wake_up() is called on &wb_ctl->done_wait after\nreleasing wb_ctl->done_lock. This creates a race window where the\nwriteback task can see num_inflight become 0, return, and free wb_ctl\nbefore zram_writeback_endio calls wake_up().\n\nCPU 0 (zram_writeback_endio) CPU 1 (writeback_store)\n============================ ============================\n zram_writeback_slots\n zram_submit_wb_request\n zram_submit_wb_request\n wait_event(wb_ctl->done_wait)\nspin_lock(&wb_ctl->done_lock);\nlist_add(&req->entry, &wb_ctl->done_reqs);\nspin_unlock(&wb_ctl->done_lock);\nwake_up(&wb_ctl->done_wait);\n zram_complete_done_reqs\nspin_lock(&wb_ctl->done_lock);\nlist_add(&req->entry, &wb_ctl->done_reqs);\nspin_unlock(&wb_ctl->done_lock);\n while (num_inflight) > 0)\n spin_lock(&wb_ctl->done_lock);\n list_del(&req->entry);\n spin_unlock(&wb_ctl->done_lock);\n // num_inflight becomes 0\n atomic_dec(num_inflight);\n\n // Leave zram_writeback_slots\n // Free wb_ctl\n release_wb_ctl(wb_ctl);\n// UAF crash!\nwake_up(&wb_ctl->done_wait);\n\nThis patch fixes this race by using RCU. By protecting wb_ctl with\nrcu_read_lock() in zram_writeback_endio and using kfree_rcu() to free it,\nwe ensure that wb_ctl remains valid during the execution of\nzram_writeback_endio."}], "id": "CVE-2026-63951", "lastModified": "2026-10-30T14:32:36.153", "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": "2026-07-19T16:17:13.837", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/bf62f69574b19720ae5fbbbcdf24a0c4e3e05e43"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/ebe2cbefc86291fa7f386447a81995640df4e2fd"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-416"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: zram: fix use-after-free in zram_writeback_endio", "id": "2502400", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2502400"}, "csaw": false, "cwe": "CWE-476", "details": ["A flaw was found in the Linux kernel's zram module. A race condition exists in the zram_writeback_endio function, which handles writeback completions. This race condition can lead to a use-after-free vulnerability, causing a system crash and resulting in a Denial of Service (DoS)."], "name": "CVE-2026-63951", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "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": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not 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-2026-63951\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-63951\nhttps://lore.kernel.org/linux-cve-announce/2026071955-CVE-2026-63951-ab46@gregkh/T"]}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[f405066a1f0db818270f49a5e96be329bcabde1e,ebe2cbefc86291fa7f386447a81995640df4e2fd)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[f405066a1f0db818270f49a5e96be329bcabde1e,bf62f69574b19720ae5fbbbcdf24a0c4e3e05e43)"}}], "enrichment": {"confidence": 99.0, "confidence_source": "inferred", "scores": [{"score": 99.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux_kernel", "vendor": "linux"}, {"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "6.19"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[0,6.19)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "semver", "value": "[7.0.12,7.1.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[7.1,*]"}}], "enrichment": {"confidence": 99.0, "confidence_source": "inferred", "scores": [{"score": 99.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux_kernel", "vendor": "linux"}], "created": "2026-07-21T06:00:01.942384+00:00", "updated": "2026-10-30T17:45:15.038367+00:00", "vendors": ["linux", "linux$PRODUCT$linux_kernel"]}