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SUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2

Type: advisorySource: Official CVE List1 source record

In the Linux kernel, the following vulnerability has been resolved: SUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2 gss_krb5_verify_mic_v2() reads the token ID at ptr[0..1], the flags byte at ptr[2], and padding at ptr[3..7], then passes ptr + GSS_KRB5_TOK_HDR_LEN and cksum_len to gss_krb5_mic_build_sg(). None of these accesses check read_token->len first. The minimum safe token size is GSS_KRB5_TOK_HDR_LEN (16) plus ctx->krb5e->cksum_len (12-24, depending on the enctype). All callers accept shorter tokens from the wire: - gss_unwrap_resp_integ() enforces only an upper bound (offset + len <= rcv_buf->len) before allocating mic.data = kmalloc(len) and passing it to gss_verify_mic(). A malicious NFS server can therefore supply a short checksum opaque, producing a small slab allocation that the Kerberos MIC verifier reads past. - gss_validate() enforces only len <= RPC_MAX_AUTH_SIZE (400) before passing the wire-supplied length to gss_validate_seqno_mic(), which constructs a mic xdr_netobj and calls gss_verify_mic(). - svcauth_gss_verify_header() enforces only checksum.len >= XDR_UNIT (4 bytes) before dispatching to gss_verify_mic(). - svcauth_gss_unwrap_integ() checks only that the checksum fits in gsd->gsd_scratch. Add a length guard at the top of gss_krb5_verify_mic_v2(), before any ptr[] access or scatterlist construction. Well-formed MIC tokens from gss_krb5_get_mic_v2() already have exactly GSS_KRB5_TOK_HDR_LEN + cksum_len bytes, so valid traffic is unaf

Announced Source revision 1
Original source ↗

CVE-2026-89537

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-2026-89537

Linux

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

Affected versions
Not stated in this record
Fixed versions
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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": "de9c17eb4a912c9028f7b470eb80815144883b26",
        "lessThan": "b2e9e10f5a536befcdce64d3e6946dff42fb823e",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "de9c17eb4a912c9028f7b470eb80815144883b26",
        "lessThan": "997577c52487181226775db3755079a3ba1d52b9",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "de9c17eb4a912c9028f7b470eb80815144883b26",
        "lessThan": "996dd15f60121bdd7896b4554458f8806d608063",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "de9c17eb4a912c9028f7b470eb80815144883b26",
        "lessThan": "7a946b2e7207f968902f2147ab9b30726f82f7ab",
        "versionType": "git"
      },
      {
        "status": "affected",
        "version": "de9c17eb4a912c9028f7b470eb80815144883b26",
        "lessThan": "b94f6719dcd9f7a609bc5f459f85795900e77d25",
        "versionType": "git"
      }
    ],
    "programFiles": [
      "net/sunrpc/auth_gss/gss_krb5_unseal.c"
    ],
    "defaultStatus": "unaffected"
  },
  {
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "vendor": "Linux",
    "product": "Linux",
    "versions": [
      {
        "status": "affected",
        "version": "2.6.35"
      },
      {
        "status": "unaffected",
        "version": "0",
        "lessThan": "2.6.35",
        "versionType": "semver"
      },
      {
        "status": "unaffected",
        "version": "6.6.160",
        "versionType": "semver",
        "lessThanOrEqual": "6.6.*"
      },
      {
        "status": "unaffected",
        "version": "6.12.114",
        "versionType": "semver",
        "lessThanOrEqual": "6.12.*"
      },
      {
        "status": "unaffected",
        "version": "6.18.57",
        "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": [
      "net/sunrpc/auth_gss/gss_krb5_unseal.c"
    ],
    "defaultStatus": "affected"
  }
]
Related CVEs
CVE-2026-89537

Source reference: /cveMetadata/cveId

Publisher severity

critical

Source reference: /containers/cna/metrics

Event
#46674 · Revision 1
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Publisher date
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