{"id":"CVE-2026-79979","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-79979","generatedAt":"2026-10-28T10:36:27.871Z","title":"This defeats the isolation that CONFIG_USERSPACE is meant to enforce, allowing information disclosure and memory corruption up to full compromise of the system.","description":"The arm64 MMU backend invalidates a single virtual address from the TLB with invalidate_tlb_page() in arch/arm64/core/mmu.c, which issued TLBI VAE1{IS} with an operand of virt >> 12. That operand encodes the ASID in bits [63:48], so the invalidation only ever matched ASID 0 (the kernel page tables) and global entries. Memory domains, however, are allocated ASIDs starting at 1 in arch_mem_domain_init(), and every domain-private leaf created by private_map() is mapped with MT_NG, i.e. non-global. A domain's cached translation therefore survived the invalidation.\n\nAll callers of invalidate_tlb_page() are demand-paging paths. When the eviction algorithm reclaims a frame, page_frame_prepare_locked() in kernel/mmu.c calls arch_mem_page_out(), which marks the kernel leaf invalid, propagates the invalid descriptor into every domain via sync_domains(), and then flushes only ASID 0. do_page_fault() immediately reuses the very same page frame for the incoming mapping through arch_mem_page_in(). A user thread that had already touched the evicted page — a k_mem_partition added with arch_mem_domain_partition_add(), or its own stack mapped by map_thread_stack() — retains a valid EL0 read/write translation to that physical frame under its own ASID.\n\nUnprivileged code running in a user thread can drive memory pressure to force eviction and then keep accessing the stale address, obtaining read and write access to whatever the kernel subsequently placed in that frame: supervisor data, another memory domain's partition, or another thread's stack. This defeats the isolation that CONFIG_USERSPACE is meant to enforce, allowing information disclosure and memory corruption up to full compromise of the system.\n\nThe fix switches the implementation to TLBI VAAE1{IS}, which matches every ASID and both global and non-global entries, so no domain-tagged translation survives a page out, dirty-bit update or access-flag clear. Exploitation requires an arm64 build with both CONFIG_USERSPACE and CONFIG_DEMAND_PAGING enabled, an active backing store, and at least one demand-paged page that is also privately mapped into a user memory domain. The same commit additionally stops globalize_table() from stripping EL0 permission and non-global attributes off domain-private leaves during paging synchronization, which previously caused user threads to lose access to their own partitions and stacks.","published":"2026-10-23T20:17:28.000Z","lastModified":"2026-10-26T13:52:22.000Z","status":"Awaiting Analysis","sourceIdentifier":"vulnerabilities@zephyrproject.org","cvss":{"version":"3.1","score":7.8,"severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H"},"cwe":["CWE-416"],"affected":[],"epss":{"score":0.00103,"percentile":0.00966,"date":"2026-10-27","history":[{"date":"2026-10-24","score":0.00144,"percentile":0.03352}]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.10%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[{"kind":"new","label":"New CVE","at":"2026-10-23T20:17:28.000Z","detail":{"score":"7.8","severity":"HIGH","publishedAt":"2026-10-23T20:17:27.783Z"},"summary":"New CVE, high severity (CVSS 7.8)."}],"references":[{"url":"https://github.com/zephyrproject-rtos/zephyr/commit/d732e9f808f16911d06769b3f756246f3528669f","source":"vulnerabilities@zephyrproject.org"},{"url":"https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-6pqm-hfxf-48qv","source":"vulnerabilities@zephyrproject.org"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-79979","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}