CVE-2026-89551 (GCVE-0-2026-89551)
Vulnerability from cvelistv5
Published
2026-09-11 19:44
Modified
2026-10-19 08:48
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: xdr_buf_trim: clamp buf->len to avoid underflow xdr_buf_trim() trims `len` bytes from the tail of an xdr_buf by walking the tail, pages, and head iovecs. Each per-section step uses min_t() so it never removes more bytes than that section holds, but the final accounting at the fix_len label subtracts the total bytes actually consumed from buf->len without any clamp: fix_len: buf->len -= (len - trim); When the caller has set buf->len to a value smaller than the sum of the iov_lens, (len - trim) can exceed buf->len and the unsigned subtraction wraps to near UINT_MAX. gss_krb5_unwrap_v2() reaches xdr_buf_trim() in exactly that state: buf->head[0].iov_len -= GSS_KRB5_TOK_HDR_LEN + headskip; buf->len = len - (GSS_KRB5_TOK_HDR_LEN + headskip); xdr_buf_trim(buf, ec + GSS_KRB5_TOK_HDR_LEN + tailskip); buf->len is a small wire-derived value while the iov_lens are at page scale, so the per-section loops legitimately consume far more bytes than buf->len records. The wrapped buf->len then propagates as the authoritative stream bound into every downstream XDR decoder. Fix by clamping the decrement so buf->len bottoms out at zero: buf->len -= min_t(unsigned int, buf->len, len - trim); On the normal path where the iov_lens sum to buf->len, (len - trim) is always <= buf->len and the result is identical to before. No callers change behavior outside the underflow case.
References
Impacted products
Vendor Product Version
Linux Linux Version: 4c190e2f913f038c9c91ee63b59cd037260ba353
Version: 4c190e2f913f038c9c91ee63b59cd037260ba353
Version: 4c190e2f913f038c9c91ee63b59cd037260ba353
Version: 4c190e2f913f038c9c91ee63b59cd037260ba353
Version: 4c190e2f913f038c9c91ee63b59cd037260ba353
Version: 4c190e2f913f038c9c91ee63b59cd037260ba353
Version: 4c190e2f913f038c9c91ee63b59cd037260ba353
Version: 4c190e2f913f038c9c91ee63b59cd037260ba353
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    "datePublished": "2026-09-11T19:44:25.327Z",
    "dateReserved": "2026-09-11T19:38:34.723Z",
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buf-\u003elen, so later xdr_read_pages/xdr_shrink_bufhead and NFS XDR decoders read far past the receive buffer into adjacent kernel memory.\\nI:H - xdr_shrink_bufhead() calls xdr_buf_head_shift_right() with a near-UINT_MAX length derived from the wrapped buf-\u003elen, and garbage xdr_stream_pos values can index the svc pages[] array out of bounds, an out-of-bounds write exploitable for control-flow hijacking.\\nA:H - Those unbounded XDR copies and the inconsistent xdr_buf (wrapped length versus iov_lens) oops or panic nfsd or the NFS client, and the peer can repeat the request at will.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"4c190e2f913f038c9c91ee63b59cd037260ba353\", \"lessThan\": \"a3d77bcd974b8625d16bddf448cb3a1b5e37049c\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4c190e2f913f038c9c91ee63b59cd037260ba353\", \"lessThan\": \"fa16bbe987b47e771e52eeb1b4540f18d92496ac\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4c190e2f913f038c9c91ee63b59cd037260ba353\", \"lessThan\": \"a924ac4c78afab71bf82641afa3b62e0c4a8b55e\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4c190e2f913f038c9c91ee63b59cd037260ba353\", \"lessThan\": \"4bf59cb0ea5b0ddfbc46a1dc2fa78fc8b9986ce4\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4c190e2f913f038c9c91ee63b59cd037260ba353\", \"lessThan\": \"e6267cccd7b05cc514e57f2160aa8db85f5c2701\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4c190e2f913f038c9c91ee63b59cd037260ba353\", \"lessThan\": \"ad0cce80d4af2f74674e8b635d97aa3880e83da8\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4c190e2f913f038c9c91ee63b59cd037260ba353\", \"lessThan\": \"85e9602650e9df07190abe817cee3b4d9bc3df17\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4c190e2f913f038c9c91ee63b59cd037260ba353\", \"lessThan\": \"3f491306dcb673ff5e78e1044ba450c58978774e\", \"versionType\": \"git\"}], \"programFiles\": [\"net/sunrpc/xdr.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"3.9\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"3.9\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.10.270\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15.221\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"6.1.188\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.157\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.12.109\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.12.*\"}, {\"status\": \"unaffected\", \"version\": \"6.18.50\", \"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/xdr.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/a3d77bcd974b8625d16bddf448cb3a1b5e37049c\"}, {\"url\": \"https://git.kernel.org/stable/c/fa16bbe987b47e771e52eeb1b4540f18d92496ac\"}, {\"url\": \"https://git.kernel.org/stable/c/a924ac4c78afab71bf82641afa3b62e0c4a8b55e\"}, {\"url\": \"https://git.kernel.org/stable/c/4bf59cb0ea5b0ddfbc46a1dc2fa78fc8b9986ce4\"}, {\"url\": \"https://git.kernel.org/stable/c/e6267cccd7b05cc514e57f2160aa8db85f5c2701\"}, {\"url\": \"https://git.kernel.org/stable/c/ad0cce80d4af2f74674e8b635d97aa3880e83da8\"}, {\"url\": \"https://git.kernel.org/stable/c/85e9602650e9df07190abe817cee3b4d9bc3df17\"}, {\"url\": \"https://git.kernel.org/stable/c/3f491306dcb673ff5e78e1044ba450c58978774e\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nSUNRPC: xdr_buf_trim: clamp buf-\u003elen to avoid underflow\\n\\nxdr_buf_trim() trims `len` bytes from the tail of an xdr_buf by\\nwalking the tail, pages, and head iovecs.  Each per-section step\\nuses min_t() so it never removes more bytes than that section\\nholds, but the final accounting at the fix_len label subtracts the\\ntotal bytes actually consumed from buf-\u003elen without any clamp:\\n\\n    fix_len:\\n            buf-\u003elen -= (len - trim);\\n\\nWhen the caller has set buf-\u003elen to a value smaller than the sum\\nof the iov_lens, (len - trim) can exceed buf-\u003elen and the unsigned\\nsubtraction wraps to near UINT_MAX.  gss_krb5_unwrap_v2() reaches\\nxdr_buf_trim() in exactly that state:\\n\\n    buf-\u003ehead[0].iov_len -= GSS_KRB5_TOK_HDR_LEN + headskip;\\n    buf-\u003elen = len - (GSS_KRB5_TOK_HDR_LEN + headskip);\\n    xdr_buf_trim(buf, ec + GSS_KRB5_TOK_HDR_LEN + tailskip);\\n\\nbuf-\u003elen is a small wire-derived value while the iov_lens are at\\npage scale, so the per-section loops legitimately consume far more\\nbytes than buf-\u003elen records.  The wrapped buf-\u003elen then propagates\\nas the authoritative stream bound into every downstream XDR\\ndecoder.\\n\\nFix by clamping the decrement so buf-\u003elen bottoms out at zero:\\n\\n    buf-\u003elen -= min_t(unsigned int, buf-\u003elen, len - trim);\\n\\nOn the normal path where the iov_lens sum to buf-\u003elen, (len - trim)\\nis always \u003c= buf-\u003elen and the result is identical to before.  No\\ncallers change behavior outside the underflow case.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.270\", \"versionStartIncluding\": \"3.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.221\", \"versionStartIncluding\": \"3.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.188\", \"versionStartIncluding\": \"3.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.157\", \"versionStartIncluding\": \"3.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.12.109\", \"versionStartIncluding\": \"3.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.18.50\", \"versionStartIncluding\": \"3.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"7.2.4\", \"versionStartIncluding\": \"3.9\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"7.3\", \"versionStartIncluding\": \"3.9\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-10-19T08:48:44.059Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-89551\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-10-19T08:48:44.059Z\", \"dateReserved\": \"2026-09-11T19:38:34.723Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2026-09-11T19:44:25.327Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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