{"id":"CVE-2026-89538","state":"PUBLISHED","title":"SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: Reject krb5 v2 wrap tokens with oversized ec field\n\ngss_krb5_unwrap_v2() sets buf->len to a logical\nlength, which can be much smaller than head[0].iov_len\n(the allocated receive-page capacity).  It then calls\nxdr_buf_trim() with a trim length derived from the 16-bit\n\"extra count\" (ec) field in the Kerberos v2 token header.\n\nThe ec field is authenticated by the post-decrypt memcmp()\nagainst the encrypted header copy, so a randomly-mutated\nvalue is rejected.  However, any peer holding a valid GSS\ncontext can legitimately encrypt a token whose ec exceeds\nthe plaintext length.  Per RFC 4121, such a token is\nstructurally malformed.\n\nAlthough xdr_buf_trim() now clamps the buf->len subtraction\nto avoid unsigned underflow, the buffer is still left in a\nsemantically invalid state (zero length, inconsistent iov\nlengths) when ec is oversized.\n\nReject these tokens before calling xdr_buf_trim(), giving\ncallers a well-defined GSS_S_DEFECTIVE_TOKEN error and\nkeeping the xdr_buf internally consistent.  The wrapped blob\nbegins at a nonzero offset -- both callers pass len as\noffset + opaque_len -- so buf->len still counts the offset\nbytes that precede the blob.  Compare the trim length\nagainst the remaining wrapped segment, buf->len - offset,\nrather than the whole buffer; comparing against buf->len\nalone leaves an offset-wide window in which an oversized ec\npasses the test and xdr_buf_trim() cuts into the bytes ahead\nof the blob.","publishedAt":"2026-09-11T19:44:15.953Z","updatedAt":"2026-10-19T08:48:29.976Z","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":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"ac9efc29346b6942e71f0e24a3178a9121330fab","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"b5746095b59f4d11f39f08751d36bbdfd1e5deac","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"4abb44a29bb515df6f49123848765c70fc9b5021","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"dfcd81ab45613d45996fbf483d4ef54b0ec90ab9","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"1f9856af065b6158271687e9788407b9573fd16f","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"880effc943ed82d6811f272ed3307c222b40f4d6","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"ad484748eec0a66eac0f13ab53b3fbedb7333c91","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sunrpc/auth_gss/gss_krb5_wrap.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.13","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.13","versionType":"semver"},{"version":"5.10.270","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.221","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.188","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/gss_krb5_wrap.c"]}],"references":["https://git.kernel.org/stable/c/ac9efc29346b6942e71f0e24a3178a9121330fab","https://git.kernel.org/stable/c/b5746095b59f4d11f39f08751d36bbdfd1e5deac","https://git.kernel.org/stable/c/9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296","https://git.kernel.org/stable/c/4abb44a29bb515df6f49123848765c70fc9b5021","https://git.kernel.org/stable/c/dfcd81ab45613d45996fbf483d4ef54b0ec90ab9","https://git.kernel.org/stable/c/1f9856af065b6158271687e9788407b9573fd16f","https://git.kernel.org/stable/c/880effc943ed82d6811f272ed3307c222b40f4d6","https://git.kernel.org/stable/c/ad484748eec0a66eac0f13ab53b3fbedb7333c91"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:26.108Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89538.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89538","state":"PUBLISHED","datePublished":"2026-09-11T19:44:15.953Z","dateUpdated":"2026-10-19T08:48:29.976Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.721Z"},"containers":{"cna":{"title":"SUNRPC: Reject krb5 v2 wrap tokens with oversized ec field","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: Reject krb5 v2 wrap tokens with oversized ec field\n\ngss_krb5_unwrap_v2() sets buf->len to a logical\nlength, which can be much smaller than head[0].iov_len\n(the allocated receive-page capacity).  It then calls\nxdr_buf_trim() with a trim length derived from the 16-bit\n\"extra count\" (ec) field in the Kerberos v2 token header.\n\nThe ec field is authenticated by the post-decrypt memcmp()\nagainst the encrypted header copy, so a randomly-mutated\nvalue is rejected.  However, any peer holding a valid GSS\ncontext can legitimately encrypt a token whose ec exceeds\nthe plaintext length.  Per RFC 4121, such a token is\nstructurally malformed.\n\nAlthough xdr_buf_trim() now clamps the buf->len subtraction\nto avoid unsigned underflow, the buffer is still left in a\nsemantically invalid state (zero length, inconsistent iov\nlengths) when ec is oversized.\n\nReject these tokens before calling xdr_buf_trim(), giving\ncallers a well-defined GSS_S_DEFECTIVE_TOKEN error and\nkeeping the xdr_buf internally consistent.  The wrapped blob\nbegins at a nonzero offset -- both callers pass len as\noffset + opaque_len -- so buf->len still counts the offset\nbytes that precede the blob.  Compare the trim length\nagainst the remaining wrapped segment, buf->len - offset,\nrather than the whole buffer; comparing against buf->len\nalone leaves an offset-wide window in which an oversized ec\npasses the test and xdr_buf_trim() cuts into the bytes ahead\nof the blob."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"ac9efc29346b6942e71f0e24a3178a9121330fab","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"b5746095b59f4d11f39f08751d36bbdfd1e5deac","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"4abb44a29bb515df6f49123848765c70fc9b5021","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"dfcd81ab45613d45996fbf483d4ef54b0ec90ab9","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"1f9856af065b6158271687e9788407b9573fd16f","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"880effc943ed82d6811f272ed3307c222b40f4d6","versionType":"git"},{"version":"cf4c024b908353fcc48309374d39e3399d67dfd1","status":"affected","lessThan":"ad484748eec0a66eac0f13ab53b3fbedb7333c91","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sunrpc/auth_gss/gss_krb5_wrap.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.13","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.13","versionType":"semver"},{"version":"5.10.270","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.221","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.188","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/gss_krb5_wrap.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/ac9efc29346b6942e71f0e24a3178a9121330fab"},{"url":"https://git.kernel.org/stable/c/b5746095b59f4d11f39f08751d36bbdfd1e5deac"},{"url":"https://git.kernel.org/stable/c/9fc6d6e6db49ab55208d5dd1c424c1d0d9aa7296"},{"url":"https://git.kernel.org/stable/c/4abb44a29bb515df6f49123848765c70fc9b5021"},{"url":"https://git.kernel.org/stable/c/dfcd81ab45613d45996fbf483d4ef54b0ec90ab9"},{"url":"https://git.kernel.org/stable/c/1f9856af065b6158271687e9788407b9573fd16f"},{"url":"https://git.kernel.org/stable/c/880effc943ed82d6811f272ed3307c222b40f4d6"},{"url":"https://git.kernel.org/stable/c/ad484748eec0a66eac0f13ab53b3fbedb7333c91"}],"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 - gss_krb5_unwrap_v2() is reached from nfsd RPCSEC_GSS privacy unwrap on TCP/2049 and from the NFS client's gss_unwrap_resp_priv() on every krb5p reply, so a remote NFS peer delivers the oversized-ec wrap token over the network.\nAC:L - A peer holding the GSS session keys can encrypt a RFC 4121 wrap token whose authenticated ec exceeds the plaintext; decrypt and the header memcmp succeed, then xdr_buf_trim() runs with that chosen length and no race or layout outside attacker control.\nPR:N - A malicious or compromised NFS server that already shares a krb5p GSS context needs no account or capability on the victim client; ordinary krb5p replies and NFSv4.0 GSS callbacks are processed without local privileges on that host.\nUI:N - Once a krb5p NFS mount exists, the client unwraps every privacy-protected reply and NFSv4.0 GSS callback with no further mount, click, or open; idle revalidations and server-driven callbacks are sufficient.\nS:U - The corrupted xdr_buf and subsequent XDR decode and shift run in the host kernel that processed the RPC and do not cross a VM, IOMMU, or sandbox boundary.\nC:H - An oversized ec makes xdr_buf_trim() underflow buf->len toward UINT_MAX, so later xdr_read_pages/xdr_shrink_bufhead use that length as a copy bound and read far past the receive buffer into adjacent kernel memory.\nI:H - xdr_shrink_bufhead() then calls xdr_buf_head_shift_right() with a near-UINT_MAX length derived from the wrapped buf->len, an out-of-bounds write into kernel memory that can be used for control-flow hijacking.\nA:H - Those unbounded XDR copies and the inconsistent xdr_buf (wrapped or zero length versus iov_lens) oops or panic nfsd or the NFS client, and the peer can repeat the request at will."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:48:29.976Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.13","versionEndExcluding":"5.10.270"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.13","versionEndExcluding":"5.15.221"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.13","versionEndExcluding":"6.1.188"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.13","versionEndExcluding":"6.6.157"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.13","versionEndExcluding":"6.12.109"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.13","versionEndExcluding":"6.18.50"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.13","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.13","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-89538","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T19:23:19.852732Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-16T19:26:41.901Z"}}]}}}