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nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref

Type: advisorySource: Official CVE List1 source record

In the Linux kernel, the following vulnerability has been resolved: nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref When CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return success with fh_dentry and fh_export both NULL if fh_verify() returns nfserr_stale and putfh->no_verify is true. The NFSD4_FH_FOREIGN flag is set, but the compound dispatch loop only uses this flag to bypass the nfserr_nofilehandle check -- it does not prevent subsequent ops from running with a NULL fh_dentry. A remote client can exploit this by crafting a COMPOUND that includes an inter-SSC COPY (which causes check_if_stalefh_allowed() to set no_verify=true on the saved PUTFH) with an additional op inserted between the source PUTFH and SAVEFH. For example, SETATTR calls fh_want_write() which dereferences fh_export->ex_path.mnt without calling fh_verify() first, causing a NULL pointer dereference in the nfsd kthread. Fix this by gating the dispatch loop: when NFSD4_FH_FOREIGN is set and fh_dentry is NULL, only OP_SAVEFH (needed for the inter-SSC flow) and ops with ALLOWED_WITHOUT_FH (which don't need a resolved filehandle) may proceed. All other ops receive nfserr_stale, per RFC 7862 Section 15.2.3 which specifies that foreign filehandle validation is deferred to the consuming operation and NFS4ERR_STALE returned at that point.

Announced Group revision 1
Original source ↗

CVE-2026-89696

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-89696

Linux

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
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Linux

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
        "lessThan": "ffdc844e673d2bcb2af8c8c3eef8cdea59d0bf32",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
        "lessThan": "00c84f4eec715e501efc080a5670114189e42507",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
        "lessThan": "2d9846fd1c767920fddd4bde30eb35cd2969df13",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
        "lessThan": "977e6f006a7a3ffc4216ae6034f768f8de6fd138",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
        "lessThan": "35f248bd40b47b229d4999581df45b97daadd977",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
        "lessThan": "311f7d926630940650447cbd1c932b076b40a6c4",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
        "lessThan": "bf4d338dc8625d70c7f2cb0657d66851a7ac9154",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "b9e8638e3d9ed8334f1f7071e081860aac37e83e",
        "lessThan": "c59738a00aa51b16adc1b5ceb7c80877168efb4d",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "fs/nfsd/nfs4proc.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "5.6"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "5.6",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "5.10.270",
        "versionType": "semver",
        "lessThanOrEqual": "5.10.*"
      },
      {
        "status": "unaffected",
        "version": "5.15.221",
        "versionType": "semver",
        "lessThanOrEqual": "5.15.*"
      },
      {
        "status": "unaffected",
        "version": "6.1.188",
        "versionType": "semver",
        "lessThanOrEqual": "6.1.*"
      },
      {
        "status": "unaffected",
        "version": "6.6.157",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.109",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.50",
        "versionType": "semver",
        "lessThanOrEqual": "6.18.*"
      },
      {
        "status": "unaffected",
        "version": "7.2.4",
        "versionType": "semver",
        "lessThanOrEqual": "7.2.*"
      },
      {
        "status": "unaffected",
        "version": "7.3",
        "versionType": "original_commit_for_fix",
        "lessThanOrEqual": "*"
      }
    ],
    "programFiles": [
      "fs/nfsd/nfs4proc.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-89696

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#35180 · Revision 1
Added to Heist Feed
Publisher date
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Revision history

  1. CVE-2026-89696 · Revision 1Source updated