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CVE-2026-89550 (GCVE-0-2026-89550)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:44 – Updated: 2026-09-14 12:00
VLAI
Title
SUNRPC: svcauth_gss: enforce krb5 token minimum length
Summary
In the Linux kernel, the following vulnerability has been resolved: SUNRPC: svcauth_gss: enforce krb5 token minimum length svcauth_gss_unwrap_priv() validates only an upper bound on the wire-supplied opaque length before handing the buffer to gss_unwrap(): if (len > xdr_stream_remaining(xdr)) goto unwrap_failed; offset = xdr_stream_pos(xdr); ... maj_stat = gss_unwrap(ctx, offset, offset + len, buf); The wire value `len` flows unchanged as the upper bound into the krb5 unwrap path, so a len in [0, 16] passes this check and is handed to gss_unwrap(). For a krb5 v2 context that lands in gss_krb5_unwrap_v2(), which reads the 16-byte RFC 4121 token header fields at ptr+4 and ptr+6 and then calls rotate_left() before any integrity check. With a sub-header length the header reads run past the token, and _rotate_left()'s `shift %= buf->len` path can divide by zero when buf->len has been driven to zero by the truncated token. A header-only token (len == 16) is equally invalid: with a non-zero RRC field and the opaque blob ending at the XDR buffer boundary, rotate_left() builds a zero-length subbuffer, reaching the same division. Reject the token at the server entry point before it reaches the krb5 unwrap core. A valid sealed RFC 4121 token must contain the 16-byte header plus at least some encrypted payload. Fix by adding a minimum-length check immediately after the existing upper-bound check: if (len <= GSS_KRB5_TOK_HDR_LEN) goto unwrap_failed;
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 7c9fdcfb1b64c47ed618c103b617af3f86e1239c , < 0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd (git)
Affected: 7c9fdcfb1b64c47ed618c103b617af3f86e1239c , < dd6afc6cab8c5d387d1ed2f069562ef7bdadd651 (git)
Affected: 7c9fdcfb1b64c47ed618c103b617af3f86e1239c , < de942dd8c2c8358bcad04ce44271954c48924423 (git)
Affected: 7c9fdcfb1b64c47ed618c103b617af3f86e1239c , < 2eed1e6a976a44015c3ee78841fe336796e2b21c (git)
Affected: 7c9fdcfb1b64c47ed618c103b617af3f86e1239c , < a919c5c88769cf8fb3ec071e6078d830bf512489 (git)
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Linux Linux Affected: 2.6.18
Unaffected: 0 , < 2.6.18 (semver)
Unaffected: 6.6.157 , ≤ 6.6.* (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)
guessed Create a notification for this product.
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sunrpc/auth_gss/svcauth_gss.c"
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              "status": "unaffected",
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: svcauth_gss: enforce krb5 token minimum length\n\nsvcauth_gss_unwrap_priv() validates only an upper bound on the\nwire-supplied opaque length before handing the buffer to\ngss_unwrap():\n\n    if (len \u003e xdr_stream_remaining(xdr))\n            goto unwrap_failed;\n    offset = xdr_stream_pos(xdr);\n    ...\n    maj_stat = gss_unwrap(ctx, offset, offset + len, buf);\n\nThe wire value `len` flows unchanged as the upper bound into the\nkrb5 unwrap path, so a len in [0, 16] passes this check and is\nhanded to gss_unwrap(). For a krb5 v2 context that lands in\ngss_krb5_unwrap_v2(), which reads the 16-byte RFC 4121 token\nheader fields at ptr+4 and ptr+6 and then calls rotate_left()\nbefore any integrity check. With a sub-header length the header\nreads run past the token, and _rotate_left()\u0027s `shift %= buf-\u003elen`\npath can divide by zero when buf-\u003elen has been driven to zero by\nthe truncated token. A header-only token (len == 16) is equally\ninvalid: with a non-zero RRC field and the opaque blob ending at\nthe XDR buffer boundary, rotate_left() builds a zero-length\nsubbuffer, reaching the same division.\n\nReject the token at the server entry point before it reaches the\nkrb5 unwrap core. A valid sealed RFC 4121 token must contain\nthe 16-byte header plus at least some encrypted payload.\n\nFix by adding a minimum-length check immediately after the\nexisting upper-bound check:\n\n    if (len \u003c= GSS_KRB5_TOK_HDR_LEN)\n            goto unwrap_failed;"
        }
      ],
      "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 - svcauth_gss_unwrap_priv() is reached from in-kernel nfsd over TCP/2049 (svc_authenticate \u2192 svcauth_gss_accept) and from the NFSv4.0 RPC_AUTH_GSS callback service, so a remote RPCSEC_GSS peer delivers the short krb5 wrap token over the network.\nAC:L - A single RPCSEC_GSS DATA Call with gc_svc=PRIVACY and opaque length in [0, 16] plus a non-zero RRC in the cleartext RFC 4121 header deterministically hits gss_krb5_unwrap_v2() rotate_left() u32 wrap and shift%=0; no race or attacker-uncontrollable layout is required.\nPR:N - A malicious NFS server that already shares a krb5p GSS context can send a crafted NFSv4.0 GSS callback into the client\u0027s svcauth_gss_unwrap_priv() with no account or capability on the victim. That peer path is the highest-severity reachability.\nUI:N - nfsd unwraps the Call in the service thread with no local user action. On the client, the NFSv4.0 GSS callback path runs from the callback service thread once an NFS/RPCSEC_GSS mount exists; no additional mount, click, or open is required at attack time.\nS:U - The out-of-bounds accesses, divide-by-zero, and underflowed memmove corrupt host kernel SUNRPC/GSS state on the machine processing the RPC. This is ordinary same-host kernel impact, not a VM escape, IOMMU bypass, or other changed-scope boundary.\nC:H - Short tokens make gss_krb5_unwrap_v2() read EC/RRC past the token, and the dead BUG_ON lets unsigned movelen underflow into a ~UINT_MAX-byte memmove that copies kernel memory beyond the receive head; that unbounded read is C:H per kernel CNA memory-corruption guidance.\nI:H - The same underflowed memmove() writes near 4GiB through the RPC receive head, an out-of-bounds write exploitable for control-flow hijack. rotate_left() also ignores xdr_buf_subsegment() failure after u32 wrap and then writes through a subbuf whose length has wrapped.\nA:H - _rotate_left() does shift %= buf-\u003elen on a zero-length subbuffer (header-only token at the XDR boundary), a divide-by-zero oops/panic; the UINT_MAX memmove and wrapped-length rotate loop hang or oops nfsd/callback threads, and the attacker can repeat the RPC to deny service."
            }
          ]
        }
      ],
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        "dateUpdated": "2026-09-14T12:00:53.633Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/dd6afc6cab8c5d387d1ed2f069562ef7bdadd651"
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        },
        {
          "url": "https://git.kernel.org/stable/c/a919c5c88769cf8fb3ec071e6078d830bf512489"
        }
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      "title": "SUNRPC: svcauth_gss: enforce krb5 token minimum length",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89550",
    "datePublished": "2026-09-11T19:44:24.572Z",
    "dateReserved": "2026-09-11T19:38:34.723Z",
    "dateUpdated": "2026-09-14T12:00:53.633Z",
    "state": "PUBLISHED"
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      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "SUNRPC: svcauth_gss: enforce krb5 token minimum length",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-89550.json",
      "version": "2"
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For a krb5 v2 context that lands in\\ngss_krb5_unwrap_v2(), which reads the 16-byte RFC 4121 token\\nheader fields at ptr+4 and ptr+6 and then calls rotate_left()\\nbefore any integrity check. With a sub-header length the header\\nreads run past the token, and _rotate_left()\u0027s `shift %= buf-\u003elen`\\npath can divide by zero when buf-\u003elen has been driven to zero by\\nthe truncated token. A header-only token (len == 16) is equally\\ninvalid: with a non-zero RRC field and the opaque blob ending at\\nthe XDR buffer boundary, rotate_left() builds a zero-length\\nsubbuffer, reaching the same division.\\n\\nReject the token at the server entry point before it reaches the\\nkrb5 unwrap core. A valid sealed RFC 4121 token must contain\\nthe 16-byte header plus at least some encrypted payload.\\n\\nFix by adding a minimum-length check immediately after the\\nexisting upper-bound check:\\n\\n    if (len \u003c= GSS_KRB5_TOK_HDR_LEN)\\n            goto unwrap_failed;\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"net/sunrpc/auth_gss/svcauth_gss.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"7c9fdcfb1b64c47ed618c103b617af3f86e1239c\",\"lessThan\":\"0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"7c9fdcfb1b64c47ed618c103b617af3f86e1239c\",\"lessThan\":\"dd6afc6cab8c5d387d1ed2f069562ef7bdadd651\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"7c9fdcfb1b64c47ed618c103b617af3f86e1239c\",\"lessThan\":\"de942dd8c2c8358bcad04ce44271954c48924423\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"7c9fdcfb1b64c47ed618c103b617af3f86e1239c\",\"lessThan\":\"2eed1e6a976a44015c3ee78841fe336796e2b21c\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"7c9fdcfb1b64c47ed618c103b617af3f86e1239c\",\"lessThan\":\"a919c5c88769cf8fb3ec071e6078d830bf512489\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"net/sunrpc/auth_gss/svcauth_gss.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"2.6.18\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"2.6.18\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.6.157\",\"lessThanOrEqual\":\"6.6.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.109\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.50\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2.4\",\"lessThanOrEqual\":\"7.2.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.3-rc1\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":9.8,\"baseSeverity\":\"CRITICAL\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":3.9,\"impactScore\":5.9}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/2eed1e6a976a44015c3ee78841fe336796e2b21c\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/a919c5c88769cf8fb3ec071e6078d830bf512489\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/dd6afc6cab8c5d387d1ed2f069562ef7bdadd651\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/de942dd8c2c8358bcad04ce44271954c48924423\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-13T06:50:24+00:00",
      "cve": "CVE-2026-89550",
      "id": "CVE-2026-89550",
      "initial_release_date": "2026-09-11T19:44:24.572000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel: Denial of Service in SUNRPC via crafted Kerberos token",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89550.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "critical",
      "current_release_date": "2026-09-13T16:58:42Z",
      "cve": "CVE-2026-89550",
      "id": "CVE-2026-89550",
      "initial_release_date": "2026-09-12T16:26:12Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89550",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89550.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.

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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.
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  • 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.


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