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CVE-2026-89679 (GCVE-0-2026-89679)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-09-13 06:33
VLAI
Title
nfsd: fix null dereference in nfsd4_setattr for deleg timestamp attrs
Summary
In the Linux kernel, the following vulnerability has been resolved: nfsd: fix null dereference in nfsd4_setattr for deleg timestamp attrs When a SETATTR request includes FATTR4_WORD2_TIME_DELEG_ACCESS or FATTR4_WORD2_TIME_DELEG_MODIFY in the attribute bitmap, nfsd4_setattr() sets deleg_attrs=true and calls nfs4_preprocess_stateid_op() to validate the stateid. If the client supplies the NFSv4 "one stateid" (all-0xFF bytes), check_special_stateids() returns nfs_ok without populating the output nfs4_stid pointer, because the special-stateid path in nfs4_preprocess_stateid_op() jumps to done: with s==NULL, and the "if (s)" block that would set *cstid is skipped. The local variable `st` remains NULL. Back in nfsd4_setattr(), the if (deleg_attrs) block then unconditionally dereferences st->sc_type (at offset 4 from NULL), causing a kernel oops. This is remotely triggerable by any NFSv4 client: send COMPOUND [PUTROOTFH, SETATTR(ONE_STATEID, {bmval2=FATTR4_WORD2_TIME_DELEG_ACCESS, ...})]. No authentication, delegation, or prior state is required. Fix by adding a NULL check before the dereference. A special stateid is not a delegation stateid, so the existing nfserr_bad_stateid return value is already correct; we only need to guard the pointer dereference itself.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 7e13f4f8d27dc02fb88666f603c53ca749d56f92 , < 3c5119b799a7f57db332b2c31e806de16c869f0f (git)
Affected: 7e13f4f8d27dc02fb88666f603c53ca749d56f92 , < 3c896db123892256fd39af0ee8c2d02c63539983 (git)
Affected: 7e13f4f8d27dc02fb88666f603c53ca749d56f92 , < fe456c8c0931bb3e8a03d429920e87fd85747fba (git)
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Linux Linux Affected: 6.14
Unaffected: 0 , < 6.14 (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
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      "affected": [
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4proc.c"
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix null dereference in nfsd4_setattr for deleg timestamp attrs\n\nWhen a SETATTR request includes FATTR4_WORD2_TIME_DELEG_ACCESS or\nFATTR4_WORD2_TIME_DELEG_MODIFY in the attribute bitmap, nfsd4_setattr()\nsets deleg_attrs=true and calls nfs4_preprocess_stateid_op() to validate\nthe stateid.\n\nIf the client supplies the NFSv4 \"one stateid\" (all-0xFF bytes),\ncheck_special_stateids() returns nfs_ok without populating the output\nnfs4_stid pointer, because the special-stateid path in\nnfs4_preprocess_stateid_op() jumps to done: with s==NULL, and the\n\"if (s)\" block that would set *cstid is skipped. The local variable `st`\nremains NULL.\n\nBack in nfsd4_setattr(), the if (deleg_attrs) block then unconditionally\ndereferences st-\u003esc_type (at offset 4 from NULL), causing a kernel oops.\n\nThis is remotely triggerable by any NFSv4 client: send COMPOUND [PUTROOTFH,\nSETATTR(ONE_STATEID, {bmval2=FATTR4_WORD2_TIME_DELEG_ACCESS, ...})].\nNo authentication, delegation, or prior state is required.\n\nFix by adding a NULL check before the dereference. A special stateid is\nnot a delegation stateid, so the existing nfserr_bad_stateid return value\nis already correct; we only need to guard the pointer dereference itself."
        }
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              "value": "AV:N - nfsd is the in-kernel NFSv4 server; nfsd4_setattr() is reached from NFSPROC4_COMPOUND over TCP/2049. A remote peer triggers it with PUTROOTFH then SETATTR; no local access to the server is required.\nAC:L - COMPOUND [PUTROOTFH, SETATTR(ONE_STATEID, FATTR4_WORD2_TIME_DELEG_ACCESS)] makes check_special_stateids() return nfs_ok with st still NULL, then nfsd4_setattr() unconditionally reads st-\u003esc_type. The crash is deterministic; no race, special layout, or rare config is required.\nPR:N - The NULL deref runs in nfsd4_setattr() before nfsd_setattr()/nfsd_permission and needs no NFSv4 session, delegation, or prior state (v4.0 COMPOUND). Default AUTH_SYS/AUTH_NULL credentials are self-asserted, so any host that can reach the NFS port can trigger it.\nUI:N - The attacker sends the crafted NFSv4 COMPOUND themselves; no victim must mount an export, open a file, or otherwise interact.\nS:U - The NULL dereference oopses an nfsd thread on the NFS server. Impact stays inside that kernel\u0027s security authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:N - This is a pure NULL-pointer read of st-\u003esc_type at offset 4 from NULL. It oopses without leaking kernel memory or providing an information-disclosure primitive.\nI:N - The bug only reads through a NULL nfs4_stid pointer; it does not write memory, corrupt adjacent objects, or yield a control-flow hijack. A remote NFS client cannot map the NULL page.\nA:H - The NULL dereference causes a kernel oops in the nfsd thread. Repeated requests can exhaust nfsd threads or panic the host (panic_on_oops), denying NFS service and taking down the server."
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          "url": "https://git.kernel.org/stable/c/3c896db123892256fd39af0ee8c2d02c63539983"
        },
        {
          "url": "https://git.kernel.org/stable/c/fe456c8c0931bb3e8a03d429920e87fd85747fba"
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    "datePublished": "2026-09-11T19:46:02.833Z",
    "dateReserved": "2026-09-11T19:38:34.747Z",
    "dateUpdated": "2026-09-13T06:33:02.395Z",
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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-13T06:51:54+00:00",
      "cve": "CVE-2026-89679",
      "id": "CVE-2026-89679",
      "initial_release_date": "2026-09-11T19:46:02.833000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel nfsd: Denial of Service via specially crafted SETATTR request",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89679.json",
      "version": "3"
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    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-16T00:00:24Z",
      "cve": "CVE-2026-89679",
      "id": "CVE-2026-89679",
      "initial_release_date": "2026-09-12T16:23:48Z",
      "product_status:known_not_affected": "353",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89679",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89679.json",
      "version": "5"
    }
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}



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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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