{"id":"CVE-2026-90039","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: Guard admin state-revocation walks with NFSD_NET_UP\n\nWriting to /proc/fs/nfsd/unlock_filesystem, or sending the\nNFSD_CMD_UNLOCK_FILESYSTEM or NFSD_CMD_UNLOCK_EXPO…","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: Guard admin state-revocation walks with NFSD_NET_UP\n\nWriting to /proc/fs/nfsd/unlock_filesystem, or sending the\nNFSD_CMD_UNLOCK_FILESYSTEM or NFSD_CMD_UNLOCK_EXPO…","severity":"medium","vendor":"Linux","product":"Linux","affected":["Linux >= 1ac3629bf012592cb0320e52a1cceb319a05ad17 < 104a51265042b4424085741c963cb858ac29ec0b","Linux >= 1ac3629bf012592cb0320e52a1cceb319a05ad17 < 0146467a2fce845cb6629979c3e9c58dd3d3a6a3","Linux >= 1ac3629bf012592cb0320e52a1cceb319a05ad17 < 2f3e6638aebc0ab8afb8b4e9816ea9a1cad85378","Linux 6.9"],"published":"2026-09-16","updated":"2026-09-21","sourceUpdated":"2026-09-21T14:17:28.123","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-90039","references":[{"url":"https://git.kernel.org/stable/c/0146467a2fce845cb6629979c3e9c58dd3d3a6a3","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/104a51265042b4424085741c963cb858ac29ec0b","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/2f3e6638aebc0ab8afb8b4e9816ea9a1cad85378","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/73bf459d696ecf207a9037bf9bb70c51a459469e","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-90039.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-90039"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2535180"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-90039"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-90039"},{"url":"https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-90039.mbox"},{"url":"https://kernelcve.org/list/?q=CVE-2026-90039"}],"tags":["nvd","cve.org","csaf","vex","red-hat"],"epss":0.00191,"epssPercentile":0.0873,"ingestedAt":"2026-09-16T10:53:53.930Z","cvss":5.5,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","cvssSource":"vendor","cwe":["CWE-476"],"slug":"CVE-2026-90039","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: Guard admin state-revocation walks with NFSD_NET_UP\n\nWriting to /proc/fs/nfsd/unlock_filesystem, or sending the\nNFSD_CMD_UNLOCK_FILESYSTEM or NFSD_CMD_UNLOCK_EXPORT netlink command,\nwalks the NFSv4 client hash tables to revoke open state and cancel\nasync COPY operations.  All three handlers gate that walk on\nnn->nfsd_serv, but a listener added via portlist or netlink\nlistener_set sets nn->nfsd_serv before any nfsd thread starts.\nnfsd_startup_net() has not yet allocated nn->conf_id_hashtbl, so the\nwalkers dereference a NULL table.  A local administrator with\nCAP_SYS_ADMIN can crash the kernel this way without ever starting the\nserver.\n\nnn->nfsd_serv is set when the service is created, which precedes\ntable allocation.  NFSD_NET_UP instead brackets the window where the\ntables are live: set at the end of nfsd_startup_net() and cleared in\nnfsd_shutdown_net() after they are freed, both under nfsd_mutex.\nGating the three unlock paths on NFSD_NET_UP fixes the startup-time\nNULL dereference while preserving the earlier post-shutdown\nuse-after-free fix.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-10-23 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-90039.json)","depth":"sunlit","depthScore":30,"depthScoreParts":{"impact":30.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":228705,"id":"CVE-2026-90039","ts":1792844923942,"field":"cvss","old":null,"new":"5.5"},{"seq":228704,"id":"CVE-2026-90039","ts":1792844923942,"field":"severity","old":"none","new":"medium"}]}