{"answers":{"affected":"It affects 1 product.","exploited":"There is no known exploitation of CVE-2026-63799 in the wild and no public exploit code.","fix":"Apply the vendor's patch.","what":"CVE-2026-63799 is a high-severity memory corruption vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2026-63799 and fix it if it is affected.\n\nWhat it is: CVE-2026-63799 is a high-severity memory corruption vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.\nExploitation: There is no known exploitation of CVE-2026-63799 in the wild and no public exploit code.\n\nAffected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.\n\nTask:\n1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.\n2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2026-63799/ (Markdown: https://insights.sbomify.com/CVE-2026-63799/index.md)","id":"CVE-2026-63799","markdown":"https://insights.sbomify.com/CVE-2026-63799/index.md","name":"CVE-2026-63799","record":{"aliases":["DEBIAN-CVE-2026-63799","GHSA-2w6g-3pwr-88wc","UBUNTU-CVE-2026-63799"],"analysis":{"component_type":"kernel","fix_type":"patch","impacts":["privilege_escalation","denial_of_service"],"network_reachable":"adjacent_or_local","non_default_config":true,"product_category":"Linux kernel","requires_auth":"low_privilege","summary":"A local attacker can trigger an out-of-bounds bit-clear in the Linux kernel scheduler, potentially causing memory corruption, system crashes, or privilege escalation.","user_interaction":"not_required","vuln_class":"memory_corruption"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"Linux","cpe":[{"product":"linux_kernel","vendor":"linux"}],"cvss":{"score":7.8,"severity":"high","source":"cna","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"},"cwes":[{"id":"CWE-125","name":"Out-of-bounds Read"}],"description":"In the Linux kernel, the following vulnerability has been resolved:\n\nsched/mmcid: Fix OOB clear_bit when CID is MM_CID_UNSET in fixup path\n\nIn mm_cid_fixup_cpus_to_tasks(), when rq-\u003ecurr has the target mm and\nmm_cid.active is set, the CID is checked with cid_in_transit() before\nsetting the transition bit.  In per-CPU mode a newly forked or exec'd\ntask can be running with mm_cid.cid == MM_CID_UNSET because CIDs are\nassigned lazily on schedule-in.  With cid_in_transit() the guard passes\nfor MM_CID_UNSET (no transit bit), converts it to MM_CID_UNSET |\nMM_CID_TRANSIT and stores it back; later mm_cid_schedout() feeds this\nto clear_bit() with MM_CID_UNSET as the bit number, triggering an\nout-of-bounds write.\n\nSymptoms: this is genuine memory corruption, but a bounded out-of-bounds\nwrite, not an arbitrary one.  MM_CID_UNSET is the fixed sentinel BIT(31),\nso once the bad value reaches mm_cid_schedout() the cid_from_transit_cid()\nstrip leaves MM_CID_UNSET, which fails the \"cid \u003c max_cids\" convergence\ntest and falls into mm_drop_cid() -\u003e clear_bit(MM_CID_UNSET,\nmm_cidmask(mm)).  The cid bitmap is embedded in the mm_struct slab object\n(after cpu_bitmap and mm_cpus_allowed) and is only num_possible_cpus()\nbits wide, so clearing bit 31 is a deterministic OOB bit-clear at a\nfixed offset of 2^31 / 8 == 256 MiB past the bitmap base.  The address is\nnot attacker-influenced (fixed sentinel -\u003e fixed offset) and the op only\nclears a single bit; what sits 256 MiB further along the direct map is\nwhatever kernel object happens to live there, so this corrupts one bit of\nunpredictable kernel memory -- it is not an arbitrary-address or\narbitrary-value write.\n\nIt triggers only in per-CPU CID mode, when a CPU is running an active\ntask of the target mm whose cid is still MM_CID_UNSET -- the\nfork()/execve() window before that task's next schedule-in assigns it a\nreal CID -- and a per-CPU -\u003e per-task fixup walks over it (the mode\nfallback driven by a thread exit, sched_mm_cid_exit(), or by the deferred\nmax_cids recompute in mm_cid_work_fn()).\n\nIn practice syzkaller surfaced it as a KASAN use-after-free reported in\n__schedule -\u003e mm_cid_switch_to, where the offending clear_bit() is inlined\nvia mm_cid_schedout() -\u003e mm_drop_cid().\n\nGuard the transition-bit assignment against MM_CID_UNSET, in addition to\nthe existing cid_in_transit() check, so the bit is only set on a genuine\ntask-owned CID.  A CPU-owned (MM_CID_ONCPU) CID of a running active task\nis handled by the cid_on_cpu(pcp-\u003ecid) branch above and never reaches\nthis path, so excluding MM_CID_UNSET (and the already-transitioning case)\nis sufficient.","ecosystems":[],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":true,"headline":"sched/mmcid: Fix OOB clear_bit when CID is MM_CID_UNSET in fixup path","id":"CVE-2026-63799","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":"linux:linux_kernel","products":["linux:linux_kernel"],"type":"memory_corruption","year":"2026"},"n_packages":0,"n_references":2,"next":{"headline":"pNFS: Fix use-after-free in pnfs_update_layout()","id":"CVE-2026-63800"},"packages":[],"prev":{"headline":"irqchip/imgpdc: Fix resource leak, add missing chained handler cleanup on remove","id":"CVE-2026-63798"},"products":["Linux"],"published":"2026-07-19","related":[{"cvss_score":8.8,"headline":"Linux Kernel Out-of-Bounds Write","id":"CVE-2026-53266","kev_date_added":"2026-09-18","published":"2026-06-25"},{"cvss_score":8.8,"headline":"Linux Kernel Improper Input Validation","id":"CVE-2013-6282","kev_date_added":"2022-09-15","published":"2013-11-19"},{"cvss_score":8.4,"headline":"Linux Kernel Heap-Based Buffer Overflow","id":"CVE-2022-0185","kev_date_added":"2024-08-21","published":"2022-02-11"},{"cvss_score":8.4,"headline":"Linux Kernel Privilege Escalation","id":"CVE-2013-2094","kev_date_added":"2022-09-15","published":"2013-05-14"},{"cvss_score":7.8,"headline":"Linux Kernel Unspecified","id":"CVE-2026-53362","kev_date_added":"2026-08-27","published":"2026-07-04"},{"cvss_score":7.8,"headline":"Linux Kernel Missing Initialization of a Variable","id":"CVE-2026-46300","kev_date_added":"2026-10-28","published":"2026-05-23"},{"cvss_score":7.8,"headline":"Linux Kernel Race Condition","id":"CVE-2025-39964","kev_date_added":"2026-09-18","published":"2025-10-13"}],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"US public information, NVD API terms","name":"NVD"},{"class":"attribution","licence":"CWE Terms of Use","name":"CWE (MITRE)"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":null,"exploitation":null,"technical_impact":null},"state":"PUBLISHED","updated":"2026-08-17","vendors":["Linux"]},"summary":"A local attacker can trigger an out-of-bounds bit-clear in the Linux kernel scheduler, potentially causing memory corruption, system crashes, or privilege escalation.","url":"https://insights.sbomify.com/CVE-2026-63799/"}