{"id":"CVE-2026-89550","state":"PUBLISHED","title":"SUNRPC: svcauth_gss: enforce krb5 token minimum length","description":"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 > 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()'s `shift %= buf->len`\npath can divide by zero when buf->len 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 <= GSS_KRB5_TOK_HDR_LEN)\n            goto unwrap_failed;","publishedAt":"2026-09-11T19:44:24.572Z","updatedAt":"2026-10-30T12:32:09.952Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"2188232509f1559cb8fcb0c9a4b1e04317fa0f15","versionType":"git"},{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd","versionType":"git"},{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"dd6afc6cab8c5d387d1ed2f069562ef7bdadd651","versionType":"git"},{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"de942dd8c2c8358bcad04ce44271954c48924423","versionType":"git"},{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"2eed1e6a976a44015c3ee78841fe336796e2b21c","versionType":"git"},{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"a919c5c88769cf8fb3ec071e6078d830bf512489","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sunrpc/auth_gss/svcauth_gss.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.18","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.109","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sunrpc/auth_gss/svcauth_gss.c"]}],"references":["https://git.kernel.org/stable/c/2188232509f1559cb8fcb0c9a4b1e04317fa0f15","https://git.kernel.org/stable/c/0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd","https://git.kernel.org/stable/c/dd6afc6cab8c5d387d1ed2f069562ef7bdadd651","https://git.kernel.org/stable/c/de942dd8c2c8358bcad04ce44271954c48924423","https://git.kernel.org/stable/c/2eed1e6a976a44015c3ee78841fe336796e2b21c","https://git.kernel.org/stable/c/a919c5c88769cf8fb3ec071e6078d830bf512489"],"weaknesses":[],"ingestedAt":"2026-10-30T12:50:04.827Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89550.json","commit":"1f312381e38164a43607eebab851b151dd16861e","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89550","state":"PUBLISHED","datePublished":"2026-09-11T19:44:24.572Z","dateUpdated":"2026-10-30T12:32:09.952Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.723Z"},"containers":{"cna":{"title":"SUNRPC: svcauth_gss: enforce krb5 token minimum length","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 > 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()'s `shift %= buf->len`\npath can divide by zero when buf->len 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 <= GSS_KRB5_TOK_HDR_LEN)\n            goto unwrap_failed;"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"2188232509f1559cb8fcb0c9a4b1e04317fa0f15","versionType":"git"},{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd","versionType":"git"},{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"dd6afc6cab8c5d387d1ed2f069562ef7bdadd651","versionType":"git"},{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"de942dd8c2c8358bcad04ce44271954c48924423","versionType":"git"},{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"2eed1e6a976a44015c3ee78841fe336796e2b21c","versionType":"git"},{"version":"7c9fdcfb1b64c47ed618c103b617af3f86e1239c","status":"affected","lessThan":"a919c5c88769cf8fb3ec071e6078d830bf512489","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sunrpc/auth_gss/svcauth_gss.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.18","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.18","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.109","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sunrpc/auth_gss/svcauth_gss.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/2188232509f1559cb8fcb0c9a4b1e04317fa0f15"},{"url":"https://git.kernel.org/stable/c/0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd"},{"url":"https://git.kernel.org/stable/c/dd6afc6cab8c5d387d1ed2f069562ef7bdadd651"},{"url":"https://git.kernel.org/stable/c/de942dd8c2c8358bcad04ce44271954c48924423"},{"url":"https://git.kernel.org/stable/c/2eed1e6a976a44015c3ee78841fe336796e2b21c"},{"url":"https://git.kernel.org/stable/c/a919c5c88769cf8fb3ec071e6078d830bf512489"}],"metrics":[{"cvssV3_1":{"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"},"scenarios":[{"lang":"en","value":"AV:N - svcauth_gss_unwrap_priv() is reached from in-kernel nfsd over TCP/2049 (svc_authenticate → 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's 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->len 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."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:32:09.952Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.18","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.18","versionEndExcluding":"6.6.157"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.18","versionEndExcluding":"6.12.109"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.18","versionEndExcluding":"6.18.50"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.18","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.18","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-89550","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T19:23:48.643149Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:26:43.119Z"}}]}}}