{"id":"CVE-2026-89689","title":"nfsd: don't free session slots that are still in use","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: don't free session slots that are still in use\n\nnfsd4_sequence() can free the very slot it is currently processing.\nWhen the session shrinker has reduced se_targe…","severity":"critical","cvss":9.8,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","cwe":["CWE-825"],"vendor":"Linux","product":"Linux","affected":["Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 < 72d40b103bb03f0124d3a3c8f71a30cbafaf6afa","Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 < b449b134e7762ddf98653a4b1d3e76d2d212ea64","Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 < f5d22e372f4ac3eb287037a488c29691d52a6330","Linux 6.14"],"published":"2026-09-11","updated":"2026-10-19","sourceUpdated":"2026-10-19T08:51:02.559Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-89689","references":[{"url":"https://git.kernel.org/stable/c/72d40b103bb03f0124d3a3c8f71a30cbafaf6afa"},{"url":"https://git.kernel.org/stable/c/b449b134e7762ddf98653a4b1d3e76d2d212ea64"},{"url":"https://git.kernel.org/stable/c/f5d22e372f4ac3eb287037a488c29691d52a6330"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89689.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-89689"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2532497"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89689"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89689"},{"url":"https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89689.mbox"},{"url":"https://access.redhat.com/errata/RHSA-2026:83207"}],"tags":["cve.org","csaf","vex","red-hat","score-dispute"],"epss":0.00614,"epssPercentile":0.492,"patched":["10base_smtv","enterprise_linux_appstream_v_10","enterprise_linux_baseos_v_10","enterprise_linux_codeready_linux_builder_v_10","enterprise_linux_hidden_v_10","enterprise_linux_real_time_for_nfv_v_10","enterprise_linux_real_time_v_10"],"scores":{"cna":9.8,"vendor":7},"ingestedAt":"2026-09-14T15:23:07.473Z","slug":"CVE-2026-89689","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: don't free session slots that are still in use\n\nnfsd4_sequence() can free the very slot it is currently processing.\nWhen the session shrinker has reduced se_target_maxslots below\nse_fchannel.maxreqs, the shrink path checks three conditions before\ncalling free_session_slots():\n\n  1. se_target_maxslots < maxreqs  (shrink was advertised)\n  2. slot->sl_generation == se_slot_gen  (slot is up-to-date)\n  3. seq->maxslots <= se_target_maxslots  (client acknowledges)\n\nHowever, seq->slotid is never checked against se_target_maxslots.\nA client using a slot in the range [se_target_maxslots, maxreqs) can\nsatisfy all three conditions: its slot has the current generation\n(set by a prior SEQUENCE), and it sends sa_highest_slotid <=\nse_target_maxslots to acknowledge the reduction.\n\nfree_session_slots() then kfrees every slot at index >=\nse_target_maxslots, including the caller's own slot. The function\ncontinues to write sl_seqid, sl_flags, sl_generation, and stores the\ndangling pointer in cstate->slot. Later, nfsd4_store_cache_entry()\ncopies up to maxresp_cached bytes of the compound reply into the freed\nsl_data[] array, corrupting whatever slab object now occupies that\naddress.\n\nAdditionally, a concurrent thread processing SEQUENCE on a different\nhigh-numbered slot can have its slot freed out from under it.\nNFSD4_SLOT_INUSE is set under nn->client_lock before the lock is\nreleased, so any concurrent thread past SEQUENCE will have its slot\nmarked. However, free_session_slots() does not check NFSD4_SLOT_INUSE\nbefore freeing.\n\nFix both problems by:\n 1. Checking that the current request's slotid is below the shrink\n    boundary.\n 2. Scanning slots in the to-be-freed range for NFSD4_SLOT_INUSE and\n    deferring the shrink if any are active.\n\n## Affected\n\n- `Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 < 72d40b103bb03f0124d3a3c8f71a30cbafaf6afa`\n- `Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 < b449b134e7762ddf98653a4b1d3e76d2d212ea64`\n- `Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 < f5d22e372f4ac3eb287037a488c29691d52a6330`\n- `Linux 6.14`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **RHSA-2026:83207** · Red Hat · fixed in: 10Base-SMTV, Red Hat Enterprise Linux AppStream (v. 10), Red Hat Enterprise Linux BaseOS (v. 10), Red Hat Enterprise Linux CodeReady Linux Builder (v. 10), Red Hat Enterprise Linux Hidden (v. 10), Red Hat Enterprise Linux Real Time for NFV (v. 10), … · released 2026-10-15 · [advisory](https://access.redhat.com/errata/RHSA-2026:83207)\n- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 6 · updated 2026-10-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89689.json)","depth":"midnight","depthScore":54,"depthScoreParts":{"impact":53.9,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":224616,"id":"CVE-2026-89689","ts":1792401438400,"field":"cvss","old":"7","new":"9.8"},{"seq":224615,"id":"CVE-2026-89689","ts":1792401438400,"field":"severity","old":"high","new":"critical"},{"seq":203900,"id":"CVE-2026-89689","ts":1789490217562,"field":"cvss","old":"7.4","new":"7"},{"seq":202980,"id":"CVE-2026-89689","ts":1789403733211,"field":"cvss","old":"9.8","new":"7.4"},{"seq":202979,"id":"CVE-2026-89689","ts":1789403733211,"field":"severity","old":"critical","new":"high"},{"seq":197738,"id":"CVE-2026-89689","ts":1789384318634,"field":"cvss","old":"7.4","new":"9.8"},{"seq":197737,"id":"CVE-2026-89689","ts":1789384318634,"field":"severity","old":"high","new":"critical"},{"seq":183675,"id":"CVE-2026-89689","ts":1789356676898,"field":"cvss","old":"9.8","new":"7.4"},{"seq":183674,"id":"CVE-2026-89689","ts":1789356676898,"field":"severity","old":"critical","new":"high"},{"seq":153568,"id":"CVE-2026-89689","ts":1789285351317,"field":"cvss","old":null,"new":"9.8"},{"seq":153567,"id":"CVE-2026-89689","ts":1789285351317,"field":"severity","old":"none","new":"critical"},{"seq":147165,"id":"CVE-2026-89689","ts":1789270198173,"field":"cvss","old":null,"new":"7.4"},{"seq":147164,"id":"CVE-2026-89689","ts":1789270198173,"field":"severity","old":"none","new":"high"},{"seq":108910,"id":"CVE-2026-89689","ts":1789183729504,"field":"cvss","old":null,"new":"7.4"},{"seq":108909,"id":"CVE-2026-89689","ts":1789183729504,"field":"severity","old":"none","new":"high"}]}