CVE-2026-89695 (GCVE-0-2026-89695)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-10-19 08:51
VLAI
Title
nfsd: cap decoded POSIX ACL count to bound sort cost
Summary
In the Linux kernel, the following vulnerability has been resolved: nfsd: cap decoded POSIX ACL count to bound sort cost nfsd4_decode_posixacl() reads a u32 entry count off the wire and passes it straight to posix_acl_alloc() and sort_pacl_range(). The latter is an O(n^2) bubble sort, so a client-chosen count drives unbounded CPU in the server's compound processing path. nfsd4_decode_posixacl() xdr_stream_decode_u32(&count) /* uncapped u32 */ posix_acl_alloc(count, GFP_KERNEL) sort_pacl_range(*acl, 0, count - 1) /* O(n^2) bubble sort */ The encoder side in the same file already rejects ACLs whose a_count exceeds NFS_ACL_MAX_ENTRIES, but the decoder introduced in commit 5fc51dfc2eb1 ("NFSD: Add support for XDR decoding POSIX draft ACLs") omitted the symmetric check. Fix by rejecting a wire count greater than NFS_ACL_MAX_ENTRIES with nfserr_inval, before any allocation, so the sort is bounded by NFS_ACL_MAX_ENTRIES^2 comparisons. While we're in here, also fix the nfserr_resource return if posix_acl_alloc() fails. That's not a legal error code for v4.1+. Change it to return nfserr_jukebox as that's more appropriate for memory allocation failures.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6971 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 5fc51dfc2eb160bd7ab3251ab1767cacf9c8bf05 , < ea14d71d6ecb925673761bcf79f781f7dc9042cc (git)
Affected: 5fc51dfc2eb160bd7ab3251ab1767cacf9c8bf05 , < 4bc1108e876153a2dd6d874052b99182c3603135 (git)
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Linux Linux Affected: 7.0
Unaffected: 0 , < 7.0 (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4xdr.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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          "vendor": "Linux",
          "versions": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.4",
                  "versionStartIncluding": "7.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "7.0",
                  "vulnerable": true
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              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: cap decoded POSIX ACL count to bound sort cost\n\nnfsd4_decode_posixacl() reads a u32 entry count off the wire and passes\nit straight to posix_acl_alloc() and sort_pacl_range(). The latter is\nan O(n^2) bubble sort, so a client-chosen count drives unbounded CPU in\nthe server\u0027s compound processing path.\n\n    nfsd4_decode_posixacl()\n      xdr_stream_decode_u32(\u0026count)       /* uncapped u32 */\n      posix_acl_alloc(count, GFP_KERNEL)\n      sort_pacl_range(*acl, 0, count - 1) /* O(n^2) bubble sort */\n\nThe encoder side in the same file already rejects ACLs whose a_count\nexceeds NFS_ACL_MAX_ENTRIES, but the decoder introduced in commit\n5fc51dfc2eb1 (\"NFSD: Add support for XDR decoding POSIX draft ACLs\")\nomitted the symmetric check.\n\nFix by rejecting a wire count greater than NFS_ACL_MAX_ENTRIES with\nnfserr_inval, before any allocation, so the sort is bounded by\nNFS_ACL_MAX_ENTRIES^2 comparisons.\n\nWhile we\u0027re in here, also fix the nfserr_resource return if\nposix_acl_alloc() fails. That\u0027s not a legal error code for v4.1+. Change\nit to return nfserr_jukebox as that\u0027s more appropriate for memory\nallocation failures."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The flaw is in nfsd\u0027s NFSv4 XDR decoder (nfsd4_decode_posixacl in fs/nfsd/nfs4xdr.c), reached when a remote client sends COMPOUND SETATTR, CREATE, or OPEN with POSIX draft ACL fattrs over TCP/2049.\nAC:L - The attacker supplies the u32 ACL count and reverse-sorted ACE payload on the wire; decode then runs sort_pacl_range() deterministically with no race, victim state, or memory-layout dependency.\nPR:N - nfsd4_decode_posixacl() runs during COMPOUND XDR decode before SEQUENCE, filehandle, export, or setattr checks; under AUTH_SYS, the common NFS flavor, RPC credentials are attacker-asserted and no secret is verified.\nUI:N - nfsd worker threads decode and sort the attacker\u0027s COMPOUND automatically; no local user or administrator action is required.\nS:U - Impact stays inside the host kernel\u0027s nfsd thread pool; this is not a VM escape, IOMMU bypass, or other cross-authority boundary.\nC:N - The bug only burns CPU while sorting a temporary decoded POSIX ACL; it does not read kernel or file contents, and a failed posix_acl_alloc() returns an NFS error without leaking memory.\nI:N - sort_pacl_range() only reorders the attacker\u0027s own temporary ACL buffer, which is discarded on error; no kernel memory is corrupted and no on-disk ACL is applied without later authorization.\nA:H - A client-chosen ACE count, practically hundreds of thousands within the 4MiB RPC payload, drives an un-preempted O(n^2) bubble sort in an nfsd thread, stalling the finite nfsd pool so repeated requests fully deny NFS service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:51:08.488Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/ea14d71d6ecb925673761bcf79f781f7dc9042cc"
        },
        {
          "url": "https://git.kernel.org/stable/c/4bc1108e876153a2dd6d874052b99182c3603135"
        }
      ],
      "title": "nfsd: cap decoded POSIX ACL count to bound sort cost",
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      }
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89695",
    "datePublished": "2026-09-11T19:46:14.258Z",
    "dateReserved": "2026-09-11T19:38:34.750Z",
    "dateUpdated": "2026-10-19T08:51:08.488Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "date": "2026-11-01",
      "epss": "0.00488",
      "percentile": "0.42013"
    },
    "nvd": {
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        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: cap decoded POSIX ACL count to bound sort cost\n\nnfsd4_decode_posixacl() reads a u32 entry count off the wire and passes\nit straight to posix_acl_alloc() and sort_pacl_range(). The latter is\nan O(n^2) bubble sort, so a client-chosen count drives unbounded CPU in\nthe server\u0027s compound processing path.\n\n    nfsd4_decode_posixacl()\n      xdr_stream_decode_u32(\u0026count)       /* uncapped u32 */\n      posix_acl_alloc(count, GFP_KERNEL)\n      sort_pacl_range(*acl, 0, count - 1) /* O(n^2) bubble sort */\n\nThe encoder side in the same file already rejects ACLs whose a_count\nexceeds NFS_ACL_MAX_ENTRIES, but the decoder introduced in commit\n5fc51dfc2eb1 (\"NFSD: Add support for XDR decoding POSIX draft ACLs\")\nomitted the symmetric check.\n\nFix by rejecting a wire count greater than NFS_ACL_MAX_ENTRIES with\nnfserr_inval, before any allocation, so the sort is bounded by\nNFS_ACL_MAX_ENTRIES^2 comparisons.\n\nWhile we\u0027re in here, also fix the nfserr_resource return if\nposix_acl_alloc() fails. That\u0027s not a legal error code for v4.1+. Change\nit to return nfserr_jukebox as that\u0027s more appropriate for memory\nallocation failures."
          }
        ],
        "id": "CVE-2026-89695",
        "lastModified": "2026-10-19T09:18:08.037",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 7.5,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "NONE",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
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              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
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        "published": "2026-09-11T20:19:56.610",
        "references": [
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            "url": "https://git.kernel.org/stable/c/4bc1108e876153a2dd6d874052b99182c3603135"
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
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      "current_release_date": "2026-10-29T13:59:24+00:00",
      "cve": "CVE-2026-89695",
      "id": "CVE-2026-89695",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "91",
      "product_status:known_not_affected": "187",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: nfsd: cap decoded POSIX ACL count to bound sort cost",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89695.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-10-20T01:03:57Z",
      "cve": "CVE-2026-89695",
      "id": "CVE-2026-89695",
      "initial_release_date": "2026-09-12T16:23:35Z",
      "product_status:known_affected": "0",
      "product_status:known_not_affected": "354",
      "product_status:recommended": "4",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89695",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2026/cve-2026-89695.json",
      "version": "6"
    }
  }
}



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