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CVE-2026-89691 (GCVE-0-2026-89691)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:46 – Updated: 2026-09-13 06:33
VLAI
Title
nfsd: clear opcnt on compound arg release to prevent OOB read
Summary
In the Linux kernel, the following vulnerability has been resolved: nfsd: clear opcnt on compound arg release to prevent OOB read nfsd4_release_compoundargs() resets args->ops to the inline iops[8] array when the dynamically-allocated ops buffer is freed, but leaves args->opcnt at its original value (which can be up to 200 for NFSv4.1+ compounds). If rq_status_counter is stuck at an odd value (which can happen when nfsd_dispatch() hits an error path after setting it odd), the RPC status dumpit handler reads min(opcnt, 16) entries from args->ops[]. Since iops only has 8 elements and is the last field in struct nfsd4_compoundargs, reading indices 8-15 accesses adjacent slab memory and leaks it to userspace via netlink. Zero opcnt unconditionally in nfsd4_release_compoundargs() so stale compound metadata is never exposed through the status interface. [ cel: Remove the kvfree_rcu_mightsleep() sleep from the exposure window ]
Severity
7.1 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: bd9d6a3efa9709e653aafbeb859289feccb8e70c , < 58bcdfb2b2e412088839ae740b1a95154dc0b8d0 (git)
Affected: bd9d6a3efa9709e653aafbeb859289feccb8e70c , < e879148867bd4c4cac42e063ffaffa187dddc6fe (git)
Affected: bd9d6a3efa9709e653aafbeb859289feccb8e70c , < c1a4f7b1848f95302df598217e1c7a1410c2d0c5 (git)
Affected: bd9d6a3efa9709e653aafbeb859289feccb8e70c , < ae4c38555e81563b8dc5eae55ffd70f0ea97aa5a (git)
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Linux Linux Affected: 6.7
Unaffected: 0 , < 6.7 (semver)
Unaffected: 6.12.109 , ≤ 6.12.* (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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{
  "containers": {
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      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4xdr.c"
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              "operator": "OR"
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: clear opcnt on compound arg release to prevent OOB read\n\nnfsd4_release_compoundargs() resets args-\u003eops to the inline iops[8]\narray when the dynamically-allocated ops buffer is freed, but leaves\nargs-\u003eopcnt at its original value (which can be up to 200 for NFSv4.1+\ncompounds).\n\nIf rq_status_counter is stuck at an odd value (which can happen when\nnfsd_dispatch() hits an error path after setting it odd), the RPC\nstatus dumpit handler reads min(opcnt, 16) entries from args-\u003eops[].\nSince iops only has 8 elements and is the last field in struct\nnfsd4_compoundargs, reading indices 8-15 accesses adjacent slab memory\nand leaks it to userspace via netlink.\n\nZero opcnt unconditionally in nfsd4_release_compoundargs() so stale\ncompound metadata is never exposed through the status interface.\n\n[ cel: Remove the kvfree_rcu_mightsleep() sleep from the exposure window ]"
        }
      ],
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
            "version": "3.1"
          },
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              "value": "AV:L - The out-of-bounds read is in nfsd_nl_rpc_status_get_dumpit(), reached only via NFSD_CMD_RPC_STATUS_GET over AF_NETLINK. Remote NFSv4 compounds can leave stale opcnt after nfsd4_release_compoundargs() but never enter dumpit, so exploitation requires local netlink access.\nAC:L - The attacker can send an NFSv4.0 COMPOUND with more than eight ops including OP_CACHEME SETCLIENTID, then a duplicate in-flight RPC so nfsd_cache_lookup() returns RC_DROPIT and leaves rq_status_counter odd. Dumpit then deterministically reads min(opcnt,16) slots from the eight-element iops array; both sides are attacker-controlled.\nPR:L - NFSD_CMD_RPC_STATUS_GET is registered with GENL_CMD_CAP_DUMP and no GENL_ADMIN_PERM, so any unprivileged process in the nfsd network namespace can invoke the dump. Exploitation does not require CAP_NET_ADMIN or init-namespace root.\nUI:N - The attacker issues the netlink dump and the NFSv4 compounds themselves. No separate victim action such as mounting a filesystem or opening a device is required.\nS:U - The slab over-read and netlink leak occur in host-kernel nfsd on the local machine. Impact stays inside one security authority and is not a VM escape, IOMMU bypass, or other cross-boundary breakout.\nC:H - After release, dumpit reads args-\u003eops[8..15].opnum past the trailing iops[8] array in nfsd4_compoundargs and returns those eight u32s via NFSD_A_RPC_STATUS_COMPOUND_OPS. That adjacent-slab out-of-bounds read is Confidentiality High unless limited to a few bytes.\nI:N - dumpit only loads opnum into a stack nfsd_genl_rqstp for netlink. There is no out-of-bounds write, use-after-free, or control-flow hijack primitive.\nA:H - Slots 8-15 are sampled at sizeof(struct nfsd4_op) stride past the kmalloc\u0027d nfsd4_compoundargs object into adjacent or unmapped slab pages, which can oops the dumpit path even if the leak is not turned into a stable read."
            }
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        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-13T06:33:16.050Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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        {
          "url": "https://git.kernel.org/stable/c/ae4c38555e81563b8dc5eae55ffd70f0ea97aa5a"
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    "cveId": "CVE-2026-89691",
    "datePublished": "2026-09-11T19:46:11.284Z",
    "dateReserved": "2026-09-11T19:38:34.749Z",
    "dateUpdated": "2026-09-13T06:33:16.050Z",
    "state": "PUBLISHED"
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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-13T06:52:12+00:00",
      "cve": "CVE-2026-89691",
      "id": "CVE-2026-89691",
      "initial_release_date": "2026-09-11T19:46:11.284000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux Kernel nfsd: Information disclosure via out-of-bounds read in compound argument release",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89691.json",
      "version": "3"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.