CVE-2026-93207 (GCVE-0-2026-93207)
Vulnerability from cvelistv5
Published
2026-09-24 15:10
Modified
2026-10-19 09:07
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: SUNRPC: Zero rpc_gss_wire_cred at svcauth_gss_decode_credbody() entry svcauth_gss_decode_credbody() writes the caller's rpc_gss_wire_cred field by field and assigns gc_ctx.len only on the success tail. The caller storage is svcdata->clcred, which lives in the per-svc_rqst gss_svc_data and is reused across requests. Early decode failures leave partially decoded state mixed with residue from the prior request. The trailing body_len tightness check is the sharpest case: xdr_stream_decode_opaque_inline() has already written gc_ctx.data with a borrowed inline pointer into the current request's XDR pages, but gc_ctx.len retains its prior value. Once the request pages are released the pooled clcred carries a dangling pointer paired with a stale length. Zero the caller's rpc_gss_wire_cred at function entry so that every early-return path leaves a deterministic all-zero cred. On the trailing tightness-check path, gc_ctx.len is now zero instead of stale, which neuters length-driven consumers such as gss_svc_searchbyctx() that would otherwise walk the dangling data pointer.
References
Impacted products
Vendor Product Version
Linux Linux Version: b0bc53470d1af01f62a0fe2d405cf56477804863
Version: b0bc53470d1af01f62a0fe2d405cf56477804863
Version: b0bc53470d1af01f62a0fe2d405cf56477804863
Version: b0bc53470d1af01f62a0fe2d405cf56477804863
Version: b0bc53470d1af01f62a0fe2d405cf56477804863
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sunrpc/auth_gss/svcauth_gss.c"
          ],
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        {
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          "product": "Linux",
          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "6.3"
            },
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              "status": "unaffected",
              "version": "0",
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              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.109",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.50",
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            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.157",
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                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.109",
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                  "vulnerable": true
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                  "versionEndExcluding": "6.18.50",
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: Zero rpc_gss_wire_cred at svcauth_gss_decode_credbody() entry\n\nsvcauth_gss_decode_credbody() writes the caller\u0027s\nrpc_gss_wire_cred field by field and assigns gc_ctx.len only on\nthe success tail.  The caller storage is svcdata-\u003eclcred, which\nlives in the per-svc_rqst gss_svc_data and is reused across\nrequests.  Early decode failures leave partially decoded state\nmixed with residue from the prior request.\n\nThe trailing body_len tightness check is the sharpest case:\nxdr_stream_decode_opaque_inline() has already written gc_ctx.data\nwith a borrowed inline pointer into the current request\u0027s XDR\npages, but gc_ctx.len retains its prior value.  Once the request\npages are released the pooled clcred carries a dangling pointer\npaired with a stale length.\n\nZero the caller\u0027s rpc_gss_wire_cred at function entry so that\nevery early-return path leaves a deterministic all-zero cred.\nOn the trailing tightness-check path, gc_ctx.len is now zero\ninstead of stale, which neuters length-driven consumers such as\ngss_svc_searchbyctx() that would otherwise walk the dangling\ndata pointer."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - A remote NFS/SUNRPC peer sends an RPC Call with flavor RPC_AUTH_GSS whose rpc_gss_cred_t fails the body_len tightness check in svcauth_gss_decode_credbody(); those cred bytes arrive on nfsd TCP/UDP 2049 via svc_recv \u2192 svc_tcp_recvfrom/svc_udp_recvfrom \u2192 svc_process \u2192 svc_process_common \u2192 svc_authenticate \u2192 svcauth_gss_accept.\nAC:L - The attacker first sends a well-formed RPCSEC_GSS cred so decode assigns gc_ctx.len, then a second Call where xdr_stream_decode_opaque_inline() succeeds but body_len != XDR_UNIT*5+xdr_align_size(handle_len). Both hit the same nfsd thread\u0027s reused gss_svc_data.clcred; the tightness failure is deterministic with no race.\nPR:N - svcauth_gss_decode_credbody() is the RPC_AUTH_GSS credential decoder inside svcauth_gss_accept(), reached before gss_svc_searchbyctx(), gss_verify_mic(), or nfsd export/client checks. Flavor 6 with auth_rpcgss registered (RPCSEC_GSS_KRB5 defaults y) needs no Kerberos ticket, uid, or capability.\nUI:N - nfsd processes each inbound RPC in the service thread via svc_process with no local user or administrator action; the attacker alone sends the residue-planting Call and the tightness-fail Call.\nS:U - The dangling gc_ctx pointer, consume_skb() of the UDP receive skb, and any later kmemdup of that pointer occur in the host nfsd/SUNRPC kernel. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - On tightness failure, xdr_stream_decode_opaque_inline() writes gc_ctx.data into the UDP in-place skb (svc_udp_recvfrom) while gc_ctx.len stays the prior handle length. svc_udp_release_ctxt() consume_skb() then frees that skb; gss_svc_searchbyctx()\u2192dup_to_netobj() kmemdups handle-\u003elen bytes from the dangling pointer, a UAF read of reclaimed kernel memory.\nI:H - The leftover clcred.gc_ctx is a use-after-free of skb-backed memory with an attacker-chosen stale length planted by the prior GSS handle. Spraying the consumed skb lets length-driven consumers of that netobj treat attacker bytes as kernel objects, so integrity impact is High as for other kernel UAFs.\nA:H - Walking gc_ctx.data after consume_skb() oopses the nfsd thread when the skb is reused or unmapped, and the attacker can repeat tightness-fail Calls to kill service threads or panic the host where panic_on_oops is set."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:07:19.480Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/56b29d62017c7dd1718d060dd5b3a2ce61095d0c"
        },
        {
          "url": "https://git.kernel.org/stable/c/0e18641708eaa8bc3c1ff338cd844aeadbd52bac"
        },
        {
          "url": "https://git.kernel.org/stable/c/e0778464049b0238f2915a40007a4154f86cf351"
        },
        {
          "url": "https://git.kernel.org/stable/c/0fa8a8acae57e6373962741d5b06d13f44aba6a9"
        },
        {
          "url": "https://git.kernel.org/stable/c/11539e8fcce0b0af062ae5fecf7b3676c2f7aeed"
        }
      ],
      "title": "SUNRPC: Zero rpc_gss_wire_cred at svcauth_gss_decode_credbody() entry",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-93207",
    "datePublished": "2026-09-24T15:10:30.942Z",
    "dateReserved": "2026-09-17T16:02:15.093Z",
    "dateUpdated": "2026-10-19T09:07:19.480Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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